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 voilà, 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.

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.