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Thursday, April 8, 2021

Which Citrus Should I Grow in My Desert Climate?

Citrus is meant for subtropical and tropical climates. Learn which how to select, grow and maintain this type of fruit in our desert.

 

Long-Lasting Effects of Freezing Temperatures

Join me on this episode of Desert Horticulture. I discuss the long-lasting effects that spring freezing temperatures can have on plants.


Saturday, April 3, 2021

Supplemental Lights Might Not Be Necessary for Citrus Growing in a Garage

Q. Because of the winter cold weather, I move my citrus trees growing in containers into my garage where it never gets below 40.  I added three fluorescent lights fixtures with grow lux bulbs per light fixture and they are hanging a few inches above the trees. Will this be sufficient light to keep the trees from being starved for light?

A. Although it’s less intense than outdoor sunlight this will work. I’m guessing you keep these citrus trees in your garage all winter long. But I’m wondering if you even need all that!

Interior of a peach flower showing the ovary. A fresh, good looking ovary after a possible freeze tells you it will probably produce a fruit.


           Winter freezing temperatures low enough to kill flowers normally start around mid-December. Usually by mid-February these temperatures are over. Although rare, sometimes we never experience freezing temperatures anywhere in the valley. Infrequently these temperatures are “patchy” and can start in mid-November (as they did in 2020) and can stretch into mid-March (as they did in 2021).

Recording Thermometer 

Inexpensive recording Taylor thermometer with two temperature probes. It used to run about $12.

Accuweather app for cell phone

Do you see why I recommend putting a recording thermometer in your landscape! I also recommend downloading a weather app on your phone for predicting upcoming freezes.

Different landscapes experience different temperatures. Oftentimes these different landscapes follow different weather patterns. These weather patterns determine your level of success in our climate. It would be much simpler for growing citrus if our climate was colder or warmer. But it’s not.

Low Light Levels Can Substitute for High Light Levels

I’m also wondering if your citrus even need the extra light. If temperatures are cold in your garage then the entire plant goes into “hibernation” and there is little need for light. For many plants this “magic temperature” is around 40 to 45° F. Also, the darkness inside the garage can delay flowering.

Because the intensity of light is so low, I would leave these lights on for 16 to 18 hours every day. Long-term low light accumulation can sometimes substitute for short-term highlight intensity (think sunlight). Because of these long light intervals, you might see earlier flowering in these trees.

 

Citrus in Containers? Maintenance More Important

Q. A horticulturalist suggested to put my dwarf citrus trees in the biggest pot I have room for or can afford and they will be happiest there. A person at a local nursery said to not move a tree from a small pot to a much larger pot and suggested the new pot be no more than 2 inches bigger in diameter than the small pot. The two questions seem to be in conflict. What do you think?


The most important practice comes about three to five years after planting into the container; replacing soil and root pruning.

A. Both answers are acceptable and pot size is not an issue as long as it is big enough. What is more important is the maintenance needed every few years for plants growing in containers. The soil in the container gets “worn out” and the roots need to be trimmed. Perhaps think about these containers like an aquarium; every few years plants in containers need to be removed, fresh soil added, the roots trimmed, and the plant repotted. This maintenance practice reinvigorates the plant and helps it live longer with fewer problems.

Selecting Citrus for Containers

Calamondin, or calamansi in the Philippines where it is native, is a small citrus that is suitable for containers. But it is sensitive to winter freezing temperatures.

When selecting citrus trees for containers make sure the tree is a dwarf or smaller in size. Smaller citrus like lime trees, calamondin, and kumquat, although variable in how much cold they can tolerate, are naturally small in stature. Oranges, lemons and larger citrus on dwarfing rootstock can also work but may be difficult to find. Look for the word “dwarf” on the label.

Containers Get Hot in the Desert

Also important is the transfer of heat from the sunny side of the container to the roots. Temperatures in the summer can be 170°F on the exposed side of the container. Consider growing container plants inside another container so the inside container is protected from direct sun by a fancy decorative exterior container. The shade from the exterior container prevents the sun from heating up the interior container.

Shade Cloth Needed for Lemon Trees?

Q. I just planted a Lisbon and Meyer lemon in full sun. Do I need to put shade cloth over them in the summer? I put shade cloth over my raised bed vegetable garden. They are planted along a northeast facing wall and not surrounded by rock.

Eureka Lemon growing in Las Vegas. Eureka lemon is a true lemon.


A. It’s a good location for fruit trees but I’m not sure how your citrus will perform in your landscape locale. Its touch and go in our climate. Much of their performance depends on the winter and spring temperatures of your landscape location. If temperatures are very low during the winter, Lisbon and Meyer trees might both get killed. Meyer lemon is more cold hardy, but in a very cold location, or during a very cold winter, it can be damaged or worse. If there are spring freezing temperatures, you might see less or no fruit produced on one or both trees.

Probably Meyer lemon which is not a true lemon. It doesnt have that lemon shape, it is round instead, and it shows off its orange heritage when it ripens but still tastes like a sweet lemon.


‘Lisbon’ is a normal lemon tree. ‘Meyer’ is not. Meyer lemon fruit tastes like a lemon but is actually a citrus hybrid with sour fruit. ‘Lisbon’ is 5 or 6 degrees more tender to winter freezing temperatures than Meyer lemon so it may need winter protection in your landscape locale when Meyer doesn’t.

Shade Protection?

Citrus doesn’t need shade protecting it from our desert sun. Citrus grows in full sun in the Yuma area, so it doesn’t need shade cloth here either. However, the first year after planting it might be a little shocked from its transfer from coastal California nursery to the harsher Mojave desert so it may develop some leaf yellowing or leaf drop the first year. Give it a chance to acclimate to this desert area which is no worse than growing in Yuma if the soil is improved at planting.

Minneola Tangelo. Orange, Pomegranate Not Producing Fruit

Q. I've had a dwarf Minneola Tangelo tree for about 4 years that gets morning sun, but I've gotten fruit off it only once. I've had an orange tree for about 1 year and a half that gets full sun; it had blossoms, but they all fell off before the heat of summer even began! I planted a pomegranate tree in full sun this past Mother's Day.  When I bought it, it had blooms on it; they also all fell off.

Unknown young pomegranate variety after maybe two years in the ground. Some pomegranate varieties are precocious...meaning they produce fruit early while other varieties produce fruit the first year. 

A. There are several different issues with your fruit trees. The Minneola Tangelo flowers only once in January and February. The same will be true of most sweet oranges. If there are freezing temperatures during this time at your landscape locale, then you may get little to no fruit when this happens. When your landscape gets winters with no freezing temperatures then each flower will produce fruit.

Late freezes

           It only takes a couple of degrees below freezing for a very short time to eliminate the flower and fruit. Multiple freezes during the spring results in total fruit loss. You may see fruit from these trees in the future, but it depends on the occurrence of spring freezing temperatures.

Be patient growing most citrus here. Citrus is more productive when there are no winter or spring freezing temperatures such as in Yuma, Arizona. Periodically we get winter freezing temperatures that can outright kill different types of citrus trees. The only reliable citrus for producing fruit in our climate are the so-called kumquats. This is because they are very cold hardy and flower all through the year.

Not Old Enough

Pomegranate loss of fruit is a different story. Pomegranate flowers through most of the year because the flowers are produced on “current season wood”; new growth and not last year’s growth. Some pomegranate varieties are more precocious than others and you will see fruit the first year they are planted. Other varieties produce fruit in the second or third year after they are in the ground. Just be patient and they will produce fruit. Plants frequently produce flowers but no fruit when they are young. It is an indicator that next year they may start fruiting.

Check Flowers of Fruit Trees for Freeze Losses

Myer lemon (not a true lemon) fruit ready for harvest. Its orange color and round shape shows off its orange fruit heritage.


Why doesn’t my ‘Meyer’ lemon tree produce any fruit? 

I was reminded of this question when I estimated the fruit production this year in a Las Vegas Orchard. I use a particular variety of pluot called ‘Flavor Supreme’ as an “indicator tree” for predicting the probable fruit load that year. I saw no fruit developing and I saw no remnants of flowers on these trees. I knew there was a late freeze that came through that orchard during the spring, probably two or three weeks ago.

Tearing open a flower soon after suspected freeze damage will tell you if the fruit will fall off dead or it is alive. In this case the ovary inside is green so it shows the flower will most likely produce a fruit.

           How did I know all that and how do I relate it back to ‘Meyer’ lemon? First of all, recognize it only takes a 1 or 2°F difference in temperature between having a tree loaded with fruit versus having a tree with few fruit. If this temperature difference comes along two or three times during the spring when it’s trying to flower, then voilĂ , there is no fruit produced that year.

All Flowers are Sensitive to Freezing

           The most tender parts to freezing temperatures of any fruit tree is its flowers. When flowers are open is the time when it is most sensitive to freezing temperatures. The tree itself is usually fine but not the flowers. If a very light freeze occurs in the spring only once when the tree is flowering, then fruit production is reduced. If a light freeze happens two or three times, maybe a week apart during the spring, then the fruit is probably eliminated for that year. However, if there is a single “hard” freeze (4 or 5 degrees below freezing or more) as flower buds are “awake” then, most likely, all fruit will be eliminated for that year.

           Flowers are killed by freezing temperatures depending on their stage of development. Flower buds during the dead of winter are very tolerant to freezing temperatures. But in the spring, when the plant begins to “wake up” from its winter sleep, they become more and more sensitive to freezing temperatures as they approach opening.

Open flowers are the most sensitive to freezing temperatures; 1°F below freezing for a very short time kills the single chance it has for fruit. Once a flower dies, it cannot produce fruit. If the flowering time of a fruit tree lasts three weeks, then it has a better chance to produce fruit as more flowers continue to open. If only 5% of the flowers are needed to produce a full load of fruit and all the flowers are dead, there is no fruit for that year.

Monday, March 29, 2021

Pollen Alert and Hay Fever

If bermudagrass flowers like this one are left to release pollen in the air, they will cause "hay fever". That's why common bermudagrass is not permitted for planting in Clark County, Nevada.

Pollen Alert

That’s what we see on our advisories in the early spring regarding pollen from mulberry, ash and junipers. The pollen alert continues through the “pollen season” as we go from mulberry to pine to olive. Pollen season might last until May. Right now we’re in “mulberry season”. Some pollen like mulberry is light enough and can be pushed by the wind and carried by pollinators like honeybees. This type of pollen causes “hay fever” while others are considered “sticky” or “heavy”, too large to travel long distances in the air and not considered allergenic.


Male flowers from the 'Bonita' ash tree. Because this ash tree is male, it produces only male flowers. Great for producing no seed but not if you dont want pollen.

Hay Fever

            “Hay fever” was a misnomer from the start. It was an old historic association with the cutting of hay in the spring and not paired with flowering of plants that cause the release of pollen. Back then pollination by plants was not studied much. Tree and shrub pollen was not considered responsible for “hayfever”. Most allergenic pollen comes from uncontrolled, wild grasses growing where rain was available. These allergies were caused by pollen floating in the air but the idea of “pollen fever” never caught on. Until recently people with severe symptoms were told to move to the desert Southwest where “pollen fever” was never considered much of a problem. Maybe that was the case back then, but they are wrong now!

Common bermudagrass flowering and it will seed next spreading pollen and seed everywhere. When bermudagrass escapes mowing, it creates pollen, allergies and seed.

Desert and Hay Fever

            As people moved to the desert Southwest and started planting more and more “desert trees” like Acacia, Mesquite and Palo Verde, “pollen fever” (aka, hayfever) developed into more of a problem. Typically, trees and shrubs with large showy flowers like oleander do not contribute much to the “hayfever problem”. This pollen is heavy or sticky and did not travel in the air far from the flower and the plants released pollen too large to cause “allergy problems”. Most of the “problem pollen” comes from “non-showy” flowers commonly found on olive, mulberry, pines, ash trees, mesquite and the like.

Oleander flowers are quite "showy". Showy flowers are not typically allergenic because the pollen is large and/or sticky.


Planting Restrictions

            Now we have planting restrictions in population dense Clark County that prohibit the planting of male mulberry trees or olive trees that produce lots of fruit. So, is it “illegal” to plant mulberry trees in Clark County? Yes and no. It is “illegal” to plant male mulberry trees but not the female trees.

Mulberry flowers are called "catkins". Flowers in mulberry are like ash trees; they are either male or female depending on the sex of the tree.

How about olive trees? Yes and no, but for a different reason. Olive trees always have both male and female parts in the same flower so we focus on the so-called “fruitless mulberries” and hope that these trees reduce “hayfever” in large communities. Mulberries, similar to ash trees, are bought as either male trees or female trees. As I have always said, plant sex is much more interesting than animal sex because of its diversity.

Olive trees are both male and female so their flowers, unlike mulberry and ash, contain both male and female parts. 

Making Pineapple Guava Set Fruit

Q. Does pineapple guava need a pollinator plant to produce fruit? The edible flowers bloom in May and have the wonderful taste of cotton candy! Should I get my pineapple guava tree a boyfriend?

Flowers of Pineapple Guava

A. First, let’s talk terms. A pollinator is an insect that helps plants produce more fruit by transferring pollen from one plant to another. Examples of pollinators are honeybees. A pollenizer is the plant that supplies this pollen to another plant to help it produce more fruit. So, I think you are asking for a pollenizer plant for pineapple guava.


A pollinator, honeybee, visiting a peach flower and it will encourage fruit set.

Now let’s talk pineapple guava. If the flowers are pollinated properly by a pineapple guava that is not exactly the same as the mother plant (pollenizer), the flowers will produce fruit. Some plants may be even self-fruitful to a degree. The amount of fruit produced depends on the number of flowers it produces and closeness to a pollenizer plant.

To make sure to get fruit from the flowers, give the plant a “boyfriend” (or girlfriend). The reason for this are because of its genetics. In technical terms, the flowers can be non-receptive to pollination by the same or similar plant (variety or cultivar) depending upon genetics. So to make sure you get fruit, plant two different varieties of a pineapple guava in close proximity, otherwise it might be a trickle of fruit at best. The flowers of pineapple guava are edible and the taste is not affected by a pollenizer.

Pineapple Guava and the Desert

Pineapple guava performs well in desert landscapes. They can handle our heat and they can handle our cold. They can even handle a lot of the rock mulch used in many landscapes. But they are “normal” water users (mesic) and not xeric like many of our native desert plants.


Flowers of pineapple guava with the same genetics are "self infertile"... in other words as much as the honeybee visits these flowers they will not set fruit. Even if the honeybee visits other pineapple guava, if they are too similar genetically then they will not create fruit. But the flowers are still yummy!

Pineapple guava is a good choice for our desert climate in landscapes, but they are not true “desert plants” so they grow better with a little bit of organics like compost mixed in the soil at planting time.

What is "Flowering Wood"?

Q. I have a star jasmine that is very woody growing behind some front greenery. I heard you mention once not to prune “flowering wood”. What does that mean?


Peach flower buds opening on peach "flowering wood". Sometimes, as in the case of peaches, the flower buds are formed the previous year they bloom. Other times flower buds (as in the case of oleander and Texas sage) they are formed on the newest spring growth. This creates a slight delay in flowering after pruning in the spring and summer months.

Texas sage (ranger) produces flowers on "current seasons wood" so if they are pruned when growing there is a pause in flowering until new growth has time to put on growth with flowers on it.

A. It means pay attention to the time of season you’re pruning and its relationship to when the plant produces flowers. 

Warning: we are talking about plants valued for their flowers, not fruit trees! Fruit trees are pruned at a different time because we value their fruit. The flowers are not as important to us in fruit trees. 

If you remember one thing, remember this; the best time to prune any plant valued for its showy flowers, is as soon as possible after it finishes flowering. Enjoy the flowers, and then prune!


Shrubs like oleander that need to put on some new growth to flower will not flower after severely cut back until it reaches close to its mature size, which in some cases can be quite large.

If it’s in the spring, prune it for flowering after it finishes in late spring. If it flowers all during the growing season, then wait until fall or winter when it stops flowering. Avoid all dramatic or “heavy” pruning of nearly all plants during the summer heat.

            Plants need time to produce flowers. Some plants also need the right time of year. If plants produce flowers all season long when growing, then wait to prune them until they finished their show by mid fall or early winter.

Probably one of the best known examples of flowering at certain times (photoperiodic flowering) is poinsettia which must only get a certain number of hours to create "flowers". Light for longer periods than this or shorter only produces green leaves.


Star jasmine typically produces flowers after a flush of spring growth; not right away in the spring. The time of flowering for this plant is more similar to oleander or Texas sage. As long as they are old enough, they start flowering as soon as there is some growth. This tells you they need a little bit of growth to produce flowers. Plants that grow like this we say f”lowers on current season wood”.

Can you see why oleander, Texas sage or star jasmine shouldn’t be pruned during the summer? Instead, they are best pruned during the winter when spring and summer growth provides the new “stem growth” needed for producing flowers. If these plants are pruned just before or after they start their new growth in the spring, it causes their flowering to “pause” until there is some new growth.

Imidacloprid, Insecticides and Safety

Q. I don't like what I'm reading about Imidacloprid (frequently found in borer control insecticides) and wanted to know if there is a better insecticide that won't harm bees.

Bayers Tree and Shrub Insect Control insecticide is one of many insecticides approved by the USEPA for killing some borers, like Emerald Ash Borer (not currently found in Nevada). 

A. You are talking about an ingredient (tiny letters on the label under active ingredients) found in several different products rather than an actual product name (big letters) found on the label. The actual or product name might be “Merit” for commercial applicators and “Bayer Tree and Shrub Spray” for homeowners but also many others

Some Countries Banned It

As a "class" of insecticides, the neonicotinoids are the most used group of manufactured insecticides in the world. Insecticides containing imidcloprid have been banned for use in some countries due to accumulated evidence. That particular ingredient is still approved for use in the United States but has faced a lot of environmental problems and may be eliminated in the future. It has been implicated in the death of some pollinators like honeybees when visiting the pollen contained in open flowers.

How to Apply it Safely

The label information for these types of products gives you a clue about how to apply it properly. If you must use this product, apply it to plants after they have finished flowering. This helps prevent the transmission of this ingredient to pollinators.

Alternatives

At this particular time I don’t know of any insecticide available or permitted for use that has the same potential for controlling borers as imidacloprid. Its major advantage is also, potentially, its disadvantage; it is a long-lived systemic insecticide that can potentially be harbored in flowers, fruit produced and plant parts for up to 12 months. The only other option I know that can work is the digging of these problem insects from infested trees as they are seen.

 

Borers can be removed from an infested limb with a sharp, sanitized knife.



Wednesday, March 17, 2021

Drawback to Woodchips: They do attract vermin

Q. My backyard has several planting beds containing roses, rosemary, mock orange, euonymus, pyracantha, lantana, sago palms, and other plants. I added rock to the soil surface eight years ago and these plants started to decline in about five years. I decided to remove the rock and put woodchips down instead but afraid of roaches entering the house from the woodchips.

Irrigation valve box amongst plants receiving water. When you combine woodchips, water and a valve box it is normal for cockroaches and spiders to live and enter there. Spray the inside of these boxes with an insecticide once a year to help reduce these numbers. But this will not stop them from helping to decompose the woodhips.

A. Insects such as cockroaches like water and something to eat. They live in the woodchips exposed to water because they help break down debris from the wood chips. Cockroaches, unpleasant as they are, are decomposers. Their favorite place to congregate in the landscape is in irrigation boxes where it stays wet. They are attracted to these wet areas and warmth of your home when it gets cold so they may come inside as their populations get larger.

Keep landscape areas close to the home dry. Apply water to landscape plants no closer than 3 feet from your house exterior walls. There isn’t a good reason to apply water closer than this. In a desert climate where there is limited rainfall, plant roots follow irrigation water. Irrigating foundation plants on the side away from the home causes their roots to grow in that direction. Keeping the soil dry surrounding your home also reduces water damage to the cement as well as reducing insect problems inside the home.

After removing the rock and before you apply woodchips, sprinkle the wet areas around plants with a rich compost to help feed the plants, enrich the soil, and start the decomposition process.

Pittman Area of Las Vegas and Managing its Soil

Q. I am a young gardener (25) in Henderson, specifically Green Valley, near the Pittman Wash. I am interested in the cultivation of plants not only for their aesthetic value, but their benefit to wildlife as well. This has steered my interests to pedology and edaphology as well as horticulture and botany.

From what I have gathered from the USDA soil survey of the Las Vegas Valley (published in 1985), my residence (and therefore garden) lies near a boundary between the ‘McCarran’ and ‘Jean-arizo’ soil series. 

From direct observation, it seems I am situated more so in the McCarran series area. With massive soil in the lower C horizon, and sticky and plastic qualities throughout, how does this effect irrigation protocols and amendments types and amounts? The reason I ask is I recently purchased some premium compost from Viragrow (thanks for the rec), and want to make sure I use the correct ratio of compost to native soil to prevent reinforcing any drainage issues associated with clay soils. The bare, native soil I am about to cultivate drains moderately slowly (some areas 15 minutes, other areas up to an hour). The only plants that have ever been in there were some poorly pruned Texas Sage (Silver and Green Cloud varieties) which have been removed. This area was not irrigated for many years, with the plants subsisting on incidental precipitation and irrigation diffusion from neighbors’ lots. The irrigation to this area has been repaired, and a large ornamental and small productive garden is now planned to be planted there. Are there any good resources, preferably more up to date than 1985, that can provide more information on local soil series and how to mitigate the inhospitable qualities of such?

A. You live in the Pittman area of Las Vegas and Henderson. 

Description of the Pittman soil series in Las Vegas and Henderson, NV.

Most native soils in that area are classified usually as “heavy” which means they have quite a bit of clay and smaller silt particles. Water drainage can be a problem in these soils if the soil is irrigated too often. For this reason, I tell people that if all the water in a hole on the property drains overnight, it’s okay. If this were Wisconsin or Iowa then it would be different. Those soils are beautiful compared to the Mojave Desert soils.

The soils for subdivisions oftentimes are imported or man-made and may not represent the native soils in those areas. If you have in imported soil on your property, then it may not be representative of the soils map. I am very familiar with NRCS soils maps for Southern Nevada and Northern Arizona, and I know the McCarran soil series quite well. It represents a huge area. So, make sure you are actually dealing with the native soil and not one that’s imported. You should be able to see that from the soil horizons. But overnight drainage for landscape soil would be okay for most landscape plants. This may not be true of Mojave native plants. If you are growing Mojave natives then I would suggest either not using an irrigation controller or using it only to water manually and not leave it on a schedule.

As far as more information is concerned, Dr. Dale Devitt (soil science researcher) and I are in the process of publishing a book that you might take a look at. It’s available on Amazon in digital form. If you want a hard copy or digital it is also available from the publisher. Dr. Devitt teaches in the biology department at UNLV. Dr. Devitt is a “hard” scientist and I consider myself a “soft” scientist who focuses mostly on transferring difficult information in terms more easily understood. Together we have published about 40 peer-reviewed scientific research articles in various journals. 

Dr. Devitt is the local soils expert and knows more than anyone about soils and water movement and plant use in the Mojave Desert. But honestly the book takes much of this difficult information from an urban tree perspective and tries to simplify it as much as possible. It’s really rehashing a lot of the same information but puts it into one book.

Any of the Cloud series of native plants (Green Cloud, Silver Cloud, etc.) will be sensitive to soils that drain poorly. Their roots will tend to die due to poor drainage. In soils like that, consider planting them on a hill or berm about a foot tall and perhaps about six feet wide. This will give the roots a chance to grow in a raised soil that will drain better.

Selecting Plants for Shade

Q. What plants can I plant in my front and backyards? I want plants that grow large enough to produce shade.

No shade on this south facing wall of this home. Wow, its hot! Shade the walls of this house to reduce electricity use in the summer. If they are deciduous then the sun can warm this house with sunlight in the winter. Shade the walls and windows. That is all that is needed, Not the roof.

A. Shade only what’s needed. This is usually the West and South windows and walls. A single-story home only needs, at the most, 25 foot-tall trees or shrubs. A two-story home can handle trees to about 35 or 40 feet tall maximum. Selecting trees taller than needed just looks “funny” when they are mature. Big trees need big spaces like parks and malls to look good.

Select Trees by Low Temperature

Winter low temperatures should be the deciding factor for permanent trees and shrubs important to the design of the landscape. There are plants used for “fun”. Fun plants can be selected for any low winter temperature. But expect damage or lose them during cold winters. In the Las Vegas Valley, use a winter temperature around 20°F minimum for the most important trees and shrubs in a landscape.

               To see which plants are available. There are three choices; buying from a local nursery or garden center, taking a road trip to buy plants, or purchasing plants online. Buying online starts around October with shipments beginning in January for spring planting of winter hardy plants. Plants bought online won’t have any soil around the roots so more care at planting time is needed.

            To aid your search for the right plant, use two places online; the plant database from the Southern Nevada water Authority or Arizona State University’s (ASU) plant database by Dr. Chris Martin. To access ASU’s plant database, type in the plants “common name” followed by “ASU”. To access Southern Nevada Water Authority’s database, start by typing in “SNWA” and “searchable database”. Pick 3 to 5 different plants in the case the plant you want is not available.

Interpreting Mojave Desert Soil though Native Plant Growth

Q. If anything, what can the different species of weeds tell someone about the soil conditions they’re found in. For example, do dandelions only grow in certain pH ranges or does puncturevine thrive only in certain sodic concentrations etc. etc.? I want to understand the most about my land via the plants that grow on it unassisted.


I apologize for the lousy picture. I took it from a slide I had made a long time ago. This is Lake Mead and showing the change in native plants (weeds) that occur with a change in soil moisture. Plants are very different closer to the Lake than further away due to less available soil moisture. As soil moisture changes, the plant communities change as well as their numbers (density) and sometimes even their height depending on the plants.

A. Which weeds are growing on native soil or disturb soils can tell you a lot. It can give hints about the chemistry of the soil and it will tell you a lot about its structure, if the soil has been disturbed or not, suitability for different plants and availability of water. 

I look at the type of weeds growing, the number of weeds and how tall they are. Wherever there is subsurface water there are a lot more plants per square meter and they are usually taller. Native soils high in phosphorus tend to favor those plants that flower more and produce seed. Crappy local native soils don’t grow much of anything. 

Dandelions for instance like disturbed soils, high phosphorus soils and they are very good at competition that’s one reason they can survive in lawns while common Bermudagrass does not. How the local plant community and the soil is managed influences which weeds grow. There are plants such as salt cedar which does favor growing in soils high in salinity but I’ve not seen a reference to sodic soils. That could be a question you could pose to Dr. Devitt

Some research questions I wanted to ask include different amounts of irrigation applied to a soil and how it influences native plant management and the value of soil amendments such as compost in influencing the management of native and exotic plants. To my knowledge none of those questions have been answered. Our soils typically are not classified as sodic soils but there are pockets (areas) of them in the valley. There are also pockets of high boron (a soil salt).

What Does "Winter-Deciduous" Mean?

 Other terms used besides Winter Deciduous include semi evergreen. It just means when it gets cold enough, it might drop its leaves because they get damaged by freezing weather, In warmer climates than Las Vegas, or if Las Vegas gets a winter with little to no freezing temperatures, then the leaves aren't damaged by the cold and they don't get damaged or may not drop. 

A change in leaf color to a "bronzing" yellowish brown can also occur. This is also a signal that it got cold. 

To reduce the chance of freezing damage, stop applying fertilizers to plants by around July 1.

This winter air temperature became so cold in this North Las Vegas location that this mesquite tree leaves were damaged, but not the tree, and they dropped. This tree, sometimes also called semi-evergreen, became deciduous.

If it gets cold enough, plants like this Star Jasmine will get yellow or bronze leaves and may even get deciduous.

Sago palm can also get cold damage during the winter if temperatures get low enough.

Bottlebrush can also get damaged from cold if winter temperatures are low enough.

Cold or freezing damage can also occur to some plants like this myoporum (locally called Australian Racer). It depends on how cold it got and for how long.

Monday, March 15, 2021

Part Time Vegetable and Herb Gardener Wanted in Las Vegas

 

Orchard at Ahern in Las Vegas

The Orchard at Ahern, located 1 ½ miles from Las Vegas Boulevard near the Center of Las Vegas, is looking for a responsible, experienced gardener, part time, to care for its vegetable and herb growing area. Ahern also owns and operates the Ahern Hotel in Las Vegas. The successful candidate would report to a Senior VP at Ahern and be responsible for the planting, growing, harvesting, and distribution of vegetables and herbs from its garden. Hours are flexible and the salary is negotiable. Interested individuals should contact Bob Morris at Extremehort@aol.com with their contact information and experience.

Thursday, March 11, 2021

How To Save Potting Soils for Future Use

Q. Should I be saving potting soils from seasonal purchase plants? I have been saving soils for years. Should the soil be thrown away at some po
int.


Garden Gourmet potting soil from Viragrow. It is made lighter in weight for containers or pots. Soil amendments like perlite, peat moss and even compost can be lighter in weight and hold water or nutrients.

A. Potting soils can be saved and reused for years. They can be valuable when added to our soils because of the “organics” they contain. These never go bad. But these “organics” don’t contain any plant nutrients and they can harbor diseases if used during their first few months after saving.

Rid this aggregated potting soil of any diseases it might contain by moistening and then placing it inside a clear plastic bag. Place this clear plastic bag full of potting soil in the summer sun for a few days. When it reaches a temperature of 180°F for 30 minutes or more, it will be sanitized of any diseases. Once sanitized, they are ready to reuse.

Rapid Summer Death of Shrubs - Collar Rot

Q. We have two 12-year-old Texas Sage shrubs concealing the street mailboxes. Within a month this past summer, they were dying back rapidly. The dieback spread over both plants. The irrigation hasn’t changed. Any idea what could be causing this? 


Not readers plant. Showing collar rot. The top dies because its choked....rotten.

A. My explanation follows the KISS principle. Texas Sage, a Chihuahuan desert native, has roots that die if watered too often. If the main stem or trunk of this shrub stays wet, this could cause it to die. My guess this is a trunk/root disease caused by watering too often. This disease moves with irrigation water and can spread easily between nearby plants.

Put Emitters Close When First Planted

When first planted, the drip emitters must be close to the plant. I like to put them up to about 12 inches during the first year. They should be moved, and more drip emitters added, as the plant gets larger in the second or third year. They are moved to about 12 to 18 inches away from the trunk at this time. This practice does not change the irrigation frequency but changes how much water is applied and where it is applied. A larger area under the plant is watered to compensate for its increased size.

            Move the drip emitters away from the trunk or main stem to a distance of 12 to 18 inches from its trunk. This should be done when the shrub is 2 to 4 years in the ground. At the same time, add more drip emitters and redistribute the emitters so that they irrigate half the area under the enlarged plant canopy. This gives the plant more water, distributes the water to a larger area because it’s larger and reduces the chance of trunk/root diseases of susceptible plants.

Mistakes Made When Planting in Desert Soils

The major mistakes made when planting are not making the planting hole wide enough, digging the hole extra deep when it’s not needed, planting too deeply, and watering the plants too often after planting.

The amount of "organics" in a soil can be "eyeballed" in many of our soils by its color. When a soil is darker in color, it means it has more "organics" in it. The Mojave Desert soils in Las Vegas have generally have no organics in them at all. This is why we add organics to the soil, oftentimes in the form of compost, to raise the level or its content. This is Garden Soil Mix from Viragrow and used for planting.

I like deals

Buying a large tree in a box and getting it planted for free is a good deal! Just have it done right. Beware. Numerous people have complained the “planting crews” dug the hole only wide enough to fit the box in the planting hole. After that a little bit of mulch is mixed with the soil, watered in, and called good. That’s no deal. The tree will decline and maybe die in a couple of years because of these poor planting techniques.

Yellowing leaves like in this bottlebrush can be a sign that the organics in the soil is running out due to its mineralization in a few years by rock mulch. Some plants dont like rock mulch but want a soil that has at least 2% organics in the soil. This soil under the rock probably has less than 1%.

Planting Right

If these deals are too good to pass up, then make sure the planting hole is at least three times the width of the box. Pay planting crews extra to do it the right way if you must. The hole doesn’t have to be dug extra deep, but it should be dug wide. It’s okay to use the soil taken from the hole for planting, but first mix it with about one third by volume of compost. If a normal compost is used, make sure to mix in some fertilizer with the soil used for the planting hole. “Rich” composts don’t need extra fertilizer in the soil mix.

Use this soil mixture for filling the planting hole around the rootball and then water it in with lots of water. Water it like this for two days in a row. Make sure the tree is watered thoroughly at planting time., To force the water deep in the planting hole, construct a “well” or “moat” 4 inches tall just above the planting hole and fill it with water.

Deep Holes - No, No, No

The planting holes shouldn’t be super deep. (unless there is a problem with drainage which is more rare than you might think). If a hole dug in the soil drains water overnight, there is no drainage problem. However, if the water is still in this hole by morning, then there is a drainage problem and other planting methods are needed. But poor drainage is not frequent in most of our landscapes.

The soil around the tree in the box or container should be “milk chocolate” in color when wet and the same level as the rest of the landscape soil when everything is finished. The tree should not be below or above the surrounding soil when finished. Make sure the soil is wet when planting.

Why Stake

Staking trees and shrubs can be very important in getting the roots established during the first year. The stakes that come with 5 and 15-gallon plants are usually good enough to reuse if cut free from the plant and pounded into the solid soil at the bottom of the planting hole so the plant roots can’t move. The purpose of staking is to keep the plant roots from moving, not necessarily the top of the plant. The top of the plant should be free to move in the wind.

Watering Shrubs Daily a Mistake. Why?

Q. I live in a climate very similar to Las Vegas; USDA Zone 8B. I planted a 1-gallon Texas ranger shrub two weeks ago in sandy/stony soil, watered them with about 2 gallons daily for 10 days. After, I put a 1-inch deep, bark mulch on the soil surface. Now, three weeks later, the leaves are yellow, brittle and crunchy on the lower stems with curling leaves on the top. I think I overwatered, but I’m not sure.

Honeysuckle crown or collar rot. A disease of plants that are watered too often.

A. Yes, sounds like they were watered too often and now probably “root dead”. Watering too often has caused the leaves to yellow, brown, and get crunchy. After the initial watering, let the soil drain water and give the plant roots air.

The plant roots drowned because the plant was continuously watered. Watering the plant with 2 gallons is about the right amount after planting. It could even be more than that. But after that, schedule the irrigations to skip at least one day so the water drains from the soil in the roots can “breathe”.

This time of year in early spring, probably once or twice a week watering is enough, even for a sandy/rocky soil! The soil around the roots was amended so it will hold water. The bark mulch on top of the soil gives you about a day extra between irrigations.

The bad news is that the soil surrounding the overwatered dead roots is probably “contaminated” with root disease problems. It could be replaced I suppose but I suggest digging a new hole for planting, at least 2 or 3 feet away from the old, contaminated hole.

Dig the hole 2 to 3 feet in diameter for a 1-gallon plant. It doesn’t have to be deep, but wide. Next, mix the soil taken from the hole with about one third compost. Wait till the last minute and finally remove the plant from the container. To do this, turn the container over and let the plant slide onto your hand. Lower the plant into the hole, holding it by its rootball, and place it so it’s resting at the bottom of the hole.

            As you are pushing this mixed soil back into the planting hole, everything is wet. Make this planting soil a “slurry” by adding water slowly to the whole with a hose so this “slurry” flows and fills all the gaps around the rootball. You should see air bubbles surfacing from this slurry. Build a moat, 2 foot wide, around the plant to force excess water down and not run off the soil surface. Fill this moat with water. Do this twice. No more than twice.

            If the plant came with a nursery stake, push it into the wet, solid soil at the bottom of the hole next to the plant and re-tie the plant to the stake with stretchable, green nursery tape. This immobilizes the plant until the roots have anchored it into the soil. Remove this stake at the end of the growing season.

            If you buy 5-gallon plants, use around five gallons of water when irrigating with the timer. If you buy 15-gallon plants, plan on around 15 gallons of applied water when irrigating. What killed the plants is watering too often, not the amount applied.

Apple -- Crown and Collar Rot

From http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=40

Vegetables like beans can have crown rot (collar rot) when planted in cold soils. Different varieties of beans will show different tolerances to cold soils and collar rot development.

 

Cause: Phytophthora cactorum and other species, a soilborne fungus-like microorganism. Crown rot is a disease of the rootstock portion of the tree; collar rot is a disease of the scion portion. Both are serious diseases of apple and other orchard trees in British Columbia, Washington, and Idaho, and have become a problem in Oregon orchards with clonal rootstocks, principally Malling Merton 106. Crabapple can also be infected.

The fungus survives primarily as oospores in soil, organic debris, or infected tissues. Oospores produce a swimming spore stage (zoospores) when soils are at or near saturation. Zoospores swim to and infect roots. Movement within roots to the root crown is greatest between pink bud and shoot elongation.

Apple crown rot in Lebanon

 

Symptoms: In early fall, an affected tree shows bronzing, purpling, or yellowing foliage of one or more limbs, accompanied by bark reddening. There is a reduction in the size of leaves and terminal growth. Examination at the root crown or collar after scraping away the soil reveals dead bark. The cambium will be orange-brown to red-brown, eventually becoming dark brown instead of white. A distinct margin may separate healthy from infected tissues. In many cases, the tree may be completely girdled before its condition is noticed. Fire blight symptoms may be similar when confined to the rootstock.

'Antonovka', 'McIntosh', and 'Wealthy' apple seedlings and M9 clonal rootstocks have shown high resistance to collar rot. Moderately resistant: MM111, M2, M7, M26, 'Golden Delicious', 'Delicious', and 'Rome Beauty'. Susceptible: MM104 and MM106.A

 


Cultural control:

  1. Plant on a raised bed to help keep water away from trunks.
  2. Avoid overirrigation.
  3. During summer, examine root crowns of trees for collar rot and scrape off diseased tissues. Leave root crowns exposed to the air until late fall.
  4. Avoid wounding root crowns. If a wound is made, keep it uncovered and open to the air for the remainder of the season.

Chemical control: Apply before symptoms appear, especially in orchards favorable for disease development. No chemical will revitalize trees showing moderate to severe crown rot symptoms. Although resistance has not been reported, alternate materials so resistant fungi do not develop quickly.

  1. Agri-Fos at 1.25 to 2.5 qt/A. Do not combine with a copper-spray program for control of other diseases. 4-hour reentry.
  2. Aliette WDG at 2.5 to 5 lb/A. Spray foliage to run off. Follow manufacturer's directions for timing of spray. Do not apply within 14 days of harvest or more than 20 lb/A per season. Do not combine with a copper spray program for control of other diseases. Phytotoxicity may result if applied within 1 week of a copper spray. 12-hr reentry.
  3. Fixed copper products. Use 4 gal solution as a drench on the lower trunk of each tree in early spring or after harvest. Do not use if soil pH is below 5.5. Not considered organic since application is to the soil.
    1. Champ Formula 2 at 2.75 pints/100 gal water. 24-hr reentry.
    2. Copper-Count-N at 4 qt/100 gal water. 12-hr reentry.
    3. Cuprofix Disperss at 5 lb/100 gal water. 24-hr reentry.
    4. Kocide DF at 4 lb/100 gal water. 48-hr reentry.
    5. Nordox 75 WG at 2.5 lb/100 gal water. 24-hr reentry.
  4. Fosphite at 1 to 3 quarts/A. Do not use copper products within 20 days of treatment and do not use spray adjuvants. May also be injected into trunk. 4-hr reentry.
  5. Phostrol at 2.5 to 5 pt/A. 4-hr reentry.
  6. Ridomil Gold SL at 0.5 pint/100 gal water. Apply diluted mixture (based on trunk size measured at 12 inches above the soil line) around each tree trunk. Apply once at planting or in spring before growth starts. Apply again in fall after harvest. 48-hr reentry.

References:
Jones, A.L. and H.S. Aldwinkle. 1990. Compendium of Apple and Pear Diseases. 1990. St. Paul, MN: APS Press.

Content edited by: Jay W. Pscheidt on January 1, 2008

Vegetables like beans can have crown rot (collar rot) when planted in cold soils. Different varieties of beans will show different tolerances to cold soils and collar rot development.


 

Cause: Phytophthora cactorum and other species, a soilborne fungus-like microorganism. Crown rot is a disease of the rootstock portion of the tree; collar rot is a disease of the scion portion. Both are serious diseases of apple and other orchard trees in British Columbia, Washington, and Idaho, and have become a problem in Oregon orchards with clonal rootstocks, principally Malling Merton 106. Crabapple can also be infected.

The fungus survives primarily as oospores in soil, organic debris, or infected tissues. Oospores produce a swimming spore stage (zoospores) when soils are at or near saturation. Zoospores swim to and infect roots. Movement within roots to the root crown is greatest between pink bud and shoot elongation.


 

Symptoms: In early fall, an affected tree shows bronzing, purpling, or yellowing foliage of one or more limbs, accompanied by bark reddening. There is a reduction in the size of leaves and terminal growth. Examination at the root crown or collar after scraping away the soil reveals dead bark. The cambium will be orange-brown to red-brown, eventually becoming dark brown instead of white. A distinct margin may separate healthy from infected tissues. In many cases, the tree may be completely girdled before its condition is noticed. Fire blight symptoms may be similar when confined to the rootstock.

'Antonovka', 'McIntosh', and 'Wealthy' apple seedlings and M9 clonal rootstocks have shown high resistance to collar rot. Moderately resistant: MM111, M2, M7, M26, 'Golden Delicious', 'Delicious', and 'Rome Beauty'. Susceptible: MM104 and MM106.A

 


Cultural control:

  1. Plant on a raised bed to help keep water away from trunks.
  2. Avoid overirrigation.
  3. During summer, examine root crowns of trees for collar rot and scrape off diseased tissues. Leave root crowns exposed to the air until late fall.
  4. Avoid wounding root crowns. If a wound is made, keep it uncovered and open to the air for the remainder of the season.

Chemical control: Apply before symptoms appear, especially in orchards favorable for disease development. No chemical will revitalize trees showing moderate to severe crown rot symptoms. Although resistance has not been reported, alternate materials so resistant fungi do not develop quickly.

  1. Agri-Fos at 1.25 to 2.5 qt/A. Do not combine with a copper-spray program for control of other diseases. 4-hour reentry.
  2. Aliette WDG at 2.5 to 5 lb/A. Spray foliage to run off. Follow manufacturer's directions for timing of spray. Do not apply within 14 days of harvest or more than 20 lb/A per season. Do not combine with a copper spray program for control of other diseases. Phytotoxicity may result if applied within 1 week of a copper spray. 12-hr reentry.
  3. Fixed copper products. Use 4 gal solution as a drench on the lower trunk of each tree in early spring or after harvest. Do not use if soil pH is below 5.5. Not considered organic since application is to the soil.
    1. Champ Formula 2 at 2.75 pints/100 gal water. 24-hr reentry.
    2. Copper-Count-N at 4 qt/100 gal water. 12-hr reentry.
    3. Cuprofix Disperss at 5 lb/100 gal water. 24-hr reentry.
    4. Kocide DF at 4 lb/100 gal water. 48-hr reentry.
    5. Nordox 75 WG at 2.5 lb/100 gal water. 24-hr reentry.
  4. Fosphite at 1 to 3 quarts/A. Do not use copper products within 20 days of treatment and do not use spray adjuvants. May also be injected into trunk. 4-hr reentry.
  5. Phostrol at 2.5 to 5 pt/A. 4-hr reentry.
  6. Ridomil Gold SL at 0.5 pint/100 gal water. Apply diluted mixture (based on trunk size measured at 12 inches above the soil line) around each tree trunk. Apply once at planting or in spring before growth starts. Apply again in fall after harvest. 48-hr reentry.

References:
Jones, A.L. and H.S. Aldwinkle. 1990. Compendium of Apple and Pear Diseases. 1990. St. Paul, MN: APS Press.

Content edited by: Jay W. Pscheidt on January 1, 2008

 

Cause: Phytophthora cactorum and other species, a soilborne fungus-like microorganism. Crown rot is a disease of the rootstock portion of the tree; collar rot is a disease of the scion portion. Both are serious diseases of apple and other orchard trees in British Columbia, Washington, and Idaho, and have become a problem in Oregon orchards with clonal rootstocks, principally Malling Merton 106. Crabapple can also be infected.

The fungus survives primarily as oospores in soil, organic debris, or infected tissues. Oospores produce a swimming spore stage (zoospores) when soils are at or near saturation. Zoospores swim to and infect roots. Movement within roots to the root crown is greatest between pink bud and shoot elongation.


 

Symptoms: In early fall, an affected tree shows bronzing, purpling, or yellowing foliage of one or more limbs, accompanied by bark reddening. There is a reduction in the size of leaves and terminal growth. Examination at the root crown or collar after scraping away the soil reveals dead bark. The cambium will be orange-brown to red-brown, eventually becoming dark brown instead of white. A distinct margin may separate healthy from infected tissues. In many cases, the tree may be completely girdled before its condition is noticed. Fire blight symptoms may be similar when confined to the rootstock.

'Antonovka', 'McIntosh', and 'Wealthy' apple seedlings and M9 clonal rootstocks have shown high resistance to collar rot. Moderately resistant: MM111, M2, M7, M26, 'Golden Delicious', 'Delicious', and 'Rome Beauty'. Susceptible: MM104 and MM106.A

 


Cultural control:

  1. Plant on a raised bed to help keep water away from trunks.
  1. Avoid overirrigation.
  1. During summer, examine root crowns of trees for collar rot and scrape off diseased tissues. Leave root crowns exposed to the air until late fall.
  1. Avoid wounding root crowns. If a wound is made, keep it uncovered and open to the air for the remainder of the season.

Chemical control: Apply before symptoms appear, especially in orchards favorable for disease development. No chemical will revitalize trees showing moderate to severe crown rot symptoms. Although resistance has not been reported, alternate materials so resistant fungi do not develop quickly.

  1. Agri-Fos at 1.25 to 2.5 qt/A. Do not combine with a copper-spray program for control of other diseases. 4-hour reentry.
  1. Aliette WDG at 2.5 to 5 lb/A. Spray foliage to run off. Follow manufacturer's directions for timing of spray. Do not apply within 14 days of harvest or more than 20 lb/A per season. Do not combine with a copper spray program for control of other diseases. Phytotoxicity may result if applied within 1 week of a copper spray. 12-hr reentry.
  1. Fixed copper products. Use 4 gal solution as a drench on the lower trunk of each tree in early spring or after harvest. Do not use if soil pH is below 5.5. Not considered organic since application is to the soil.
  1. Champ Formula 2 at 2.75 pints/100 gal water. 24-hr reentry.
  1. Copper-Count-N at 4 qt/100 gal water. 12-hr reentry.
  1. Cuprofix Disperss at 5 lb/100 gal water. 24-hr reentry.
  1. Kocide DF at 4 lb/100 gal water. 48-hr reentry.
  1. Nordox 75 WG at 2.5 lb/100 gal water. 24-hr reentry.
  1. Fosphite at 1 to 3 quarts/A. Do not use copper products within 20 days of treatment and do not use spray adjuvants. May also be injected into trunk. 4-hr reentry.
  1. Phostrol at 2.5 to 5 pt/A. 4-hr reentry.
  1. Ridomil Gold SL at 0.5 pint/100 gal water. Apply diluted mixture (based on trunk size measured at 12 inches above the soil line) around each tree trunk. Apply once at planting or in spring before growth starts. Apply again in fall after harvest. 48-hr reentry.

References:

Jones, A.L. and H.S. Aldwinkle. 1990. Compendium of Apple and Pear Diseases. 1990. St. Paul, MN: APS Press.

Content edited by: Jay W. Pscheidt on January 1, 2008