Spider Mites Can Occur after Applying Hard Pesticides

Q. I have a fruit tree with leaves that are brown on the edges and a dust that covers the leaves. Some of the leaves are turning gray green on branches and the tree does not look healthy.

Spider mites our famous for causing damage to Italian cypress. They cause Browning and branch death, usually there is webbing seen as well. That's why these critters are called "spider" mites. But they are more closely related to spiders than they are insects.It's always a good idea to wash off Italian cypress with a hose when they get dusty.

A. Most likely the tree damage was caused by spider mites. Spider mites are a summer pest problem during hot, dry weather.

            Another telltale sign that you mentioned is the “dusty” appearance of the leaves. This “dust” results from dead spider mites left behind as the population grows.

            Look for feeding damage to the leaves caused by spider mites. This feeding damage causes tiny yellow dots scattered all over the surface of the leaf and accompanied by tiny black dots the size of this period. By the way, the tiny black dots is mite “poop”. Even though mites feed on leaf bottoms, the yellow dots can be seen on the top of leaves.

            A common misconception is that webbing must be present if mites are the problem. Spider mites leave behind “webbing”, like the weak form of a spider’s web. But not all mites that cause plant damage spin webs.

Leaf damage and webbing scene on tomatoes caused by spider mites.

            So, finding webs when there is damage is not a “dead giveaway” that the damage is from mites. It could be one indicator, though. There are real spiders who are “good guys” that spin webs and hang out in plants. These spiders can be beneficial.

            Mite attacks to plants may come after the application of a hard pesticide. Bad mites are always present on plants but their numbers are controlled by predatory insects and even “good mites”. So, applying a hard pesticide to control borers, for instance, could lead to an outbreak of spider mites because the predatory “good guys” were killed.

            What can you do? Confirm that spider mites are the problem. Use a white paper test. Shake or slap an infested branch on a white piece of paper or paper plate. Closely look at the white surface for tiny dots, the size of a period, crawling along the paper.

            Smear them with your fingers if you aren’t sure. If you see lots of them, along with plant damage that I described, you have confirmed mite damage.

            Multiple applications of soap and water sprays do a good job getting small outbreaks under control. Hosing the leaves of plants monthly, or after a dust storm, removes dust from the leaf surface which can increase spider mite populations.

            Severe infestations of spider mites may require a pesticide application. Whenever spider mites were problem during the year, be sure to apply two dormant oil sprays during the winter months.

Best Distance of Palms to Walls is Ten Feet

Q. I have two Mexican fan palms in my backyard that are 16-18 feet tall. One is 3 feet from a retaining wall and 6 feet from a pool. Another is 3 feet from the corner of my house which is on a slab. Do I need to worry about the roots damaging the wall, pool or slab?

Way too close for palms to be planted to a wall.

A. The short answer is you should be concerned anytime something that can get large is growing close to anything that can be damaged. The good news is that palm roots don’t typically damage walls, swimming pools and concrete slabs as much as other types of tree roots. But they can cause damage.

            Palms in general are not a good choice around pools but Mexican fan palms get huge and should never be planted close to structures. Smaller palms, such as windmill and Mediterranean fan palm, would be a better choice. The closest large fan palms should be planted to walls, swimming pools and house slabs are perhaps 10 feet away.

Palms look beautiful near a pool but they can cause problems and very messy when they drop seed.

            There are a couple of options if you don’t want to remove these palms. One is installing a root barrier so that palm roots are deflected away from structures that could be damaged. Root barriers are installed and extend about 30 inches deep or more and reside slightly above soil level.

            The second option is to use water for directing root growth. In deserts soils are normally dry due to a lack of rain. Tree roots grow where water is available. By placing irrigation water away from walls, cool decking or a house foundation we can direct tree root growth away from these potential problem areas.

            Water does not need to be applied evenly under plant canopies. I recommend keeping water 2 – 3 feet away from these potential problem areas.

Correcting Borer Damage in Italian Cypress

Q. My Italian cypress started to lose their color and then die. Upon inspection of the trunk, I saw borers in them. Borers seemed to take place within two months or so and killed a few mature trees. I treated them with Bayer Tree and Shrub Insect Control but wanted to know if there is anything else I can do to help save them.

Borer damage found in Italian cypress trunk

Bora damage found in another Italian cypress trunk

Suspected board damage found in Italian Cypress

A. Damage from borers or boring insects is typically a slower progression than a couple of months unless the plants are small. You are right, the progression in many plants is a change in color from a vibrant green to a dull, gray green color as the limb and leaves are dying from a lack of water.

            My guess is borer damage to your trees started before this year. Internal damage to the trunk from borers can be present for several years before enough damage has accumulated to result in the death of older trees. If trees are growing vigorously, they can recover from light borer damage on an annual basis.

            This color change due to damage starts in midsummer when air temperatures begin to heat up and plants require more water. Damage from boring insects begins in mid-spring (March) but get progressively more intense as these insects become larger and more voracious feeders.  By midsummer (June and later) internal damage to limbs and the trunk can be extensive, unrecoverable by the plant, and the supply of water from the roots is cut off.

Homeowners have this product available for borer control containing Imidacloprid in the active ingredients. It comes in other names as well. It is always best to check the active ingredients to make sure. Apply it late spring after any flowering has occured to avaid possible problems with honeybees. This chemical has been implicated, not proven, in colony collapse of honeybees. The safest way to apply it in our environment is a soil drench. Always read the label before applying any chemical.

            You chose the correct insecticide to use but it was probably applied too late. The best time to control boring insects with these types of insecticides is in mid spring when they first become active.

            Consider using pesticides as a last resort because they can be a bit like “whack-a-mole” and contribute to other pest problems. Death of boring insects can happen in a few days when systemic insecticides are applied as a liquid drench to the soil.

Repairing Plum Tree from Borer Damage

Q. I have a ‘Green Gage’ plum tree that is 18 years old and produces plenty of plums each year. In August I saw sap coming out of one branch and along the trunk in several places.  Last week the bark started to separate and it looks like the trunk is starting to split. The leaves on that limb are starting to die. This side of the tree receives the west sun. All the other branches on the tree appear to be fine.

A. Green Gauge is a good plum for our desert climate and 18 is not old for a plum tree. Plums can be “sappy” compared to other fruit trees but from your description it sure sounds like borers. You won’t hurt anything, but I would take a very sharp knife that has been sanitized and start actively looking for borers.

            It is possible to remove the outer layer of bark covering the trunk and limbs and reveal the immature form of this insect, called the larva, causing the damage. Once exposed like this, it will die.

            Expose all the damage caused by borers down to healthy wood. Leave this exposed area open for healing.  I would say that about 80% of the time this is an effective way to remove the borer and allow the limb to recover.

What I Would Do

I would first remove some bark on top of the area where I think borers might be residing. Hold the sharp knife nearly flat and push the blade away from you to remove the bark. After removal, inspect the wood to see if it is alive or dead. If it is alive, stop and don't do anything more. If it is dead, remove all of this dead bark until you see bark that is alive. If you find evidence of borers, try to find them in this dead area and remove them. If the borer damage is extensive it might require removal of the limb or branch. Do not paint this area but let it heal in the open air.

Using a sharp, sanitized knife to remove the bark that surrounds a borer infested limb.

Removal of the dead wood caused by borers

Successful removal of borers the previous year and the tree showing signs of healing.

African Sumac Attacked by Borers

Q. What should I do now with my 14-year-old, damaged African sumac? I think it had borers as you mentioned in a previous column, but the tree top is lush and green and showing no dieback of the limbs.

A. Many older trees damaged by borers show only subtle, outward signs of damage. Early borer damage is difficult to see. It isn’t until damage is extensive, usually from attacks every year, does it become obvious to the casual observer because of limb dieback.

This is a Purple Robe locust but it developed sunburn on the side facing the sun and this damaged area was followed up by an attack of borers. 

            I can see in the picture you sent that the borer damage to the trunk is healing. Encourage this type of healing with regular watering coupled with fertilizer applications twice a year. If it hasn’t been fertilized during the past 12 months, make an application when temperatures cool off a bit.

            The best time to see “hidden damage” in the spring done by borers is immediately after a good rain. Damage to trees due to borers is expressed through the wet trunk or limbs as a reddish, jellylike ooze. If not seen right away, this “jelly” dries in a day or two leaving reddish crystals behind.

Sap can sometimes be seen from trees attacked by boring insects. The best time to see this sap losing from the tree is immediately after rain.

            It looks like a limb broke and ripped the trunk, perhaps as it fell. This could have been because of previous borer problems that weakened the tree at this location. The central core of all trees is dead and surrounded by a cylinder of living tissue that can heal these types of wounds.

Sometimes trees can recover from an attack by boars if they are removed with a sharp knife or killed with a systemic insecticide.

            This living cylinder can be thick or thin depending on tree health. When trees are healthy and vigorous, this living cylinder repairs damage quickly by “rolling over” damaged areas as seen in your picture. Large areas can heal over in a couple seasons of growth if the tree is healthy.

Problems With Bottle Trees Growing in the Desert

Q. My bottle tree trunk is turning somewhat of a burgundy color. I live in Las Vegas and they were planted just over a month ago. Some leaves are brown in full and some partially but overall seems alright minus the trunk having that reddish tone while the other 3 are greenish grey. 

A. I get more questions about this tree than probably any other. It has been touted as a "desert tree", but is it? Bottle trees are not really DESERT trees but more Mediterranean in their semi-arid agroclimatic origins. Think more like palms, olives, rosemary and even oleander.

Discoloration of the limbs

The "skin" or trunk and limb surfaces are photosynthetic (green) which means that they can manufacture its own energy besides 100% by the leaves as trees with dark brown limbs and trunk can. Some trees that have this quality can handle high light intensities that come with an open canopy.

Sunburn on bottle tree limbs. Notice that sunburn happens on the upper limb surfaces exposed to direct sunlight.

Unfortunately bottle tree of this type (Brachychiton populneus) doesn't appear that it can. When the canopy opens up because of leaf drop or a thin canopy the upper sides of the limbs can "burn". Frequently this may cause interference with the water transport to the leaves. But if at least half of the limb is unaffected, the tree should survive.

Drought

Even bottle trees can suffer from a lack of water. Watering every day can still result in drought IF the amount of water applied does not meet its need for water.

A usual sign that a tree is not getting enough water is a thinning of  its canopy. Bottle trees can also drop leaves in midsummer,as reported by some homeowners in Phoenix. A bit unsettling when you don't know what the leaf drop means.

Drainage

Bottle trees do well in lawns if the soil drains water well. 

Young bottle tree growing in a lawn

Causes of Raywood Ash Trees and Dying Branches

Q. We have two Raywood ash trees that are loosing whole branches and more from either a systemic disease or insects. The trees are about 23 years old and well cared for. Damage starts at the terminus of the branches and soon involves the whole branch leaving the leaves a light tan color over the entire branch and limb.  We have used Bayer systemic pesticide topically over the area of irrigation.

Ash tree planted  with rock surface mulch surrounding it and leaf scorch.. Probably too hot in this location and perhaps not enough water applied.

A. Three possible problems exist for that tree; drought, borers and a disease called ash decline. It is not a good tree if it is surrounded by rock mulch. It is more of a “mesic” tree which means it is better off in a mixed landscape, or a part of the landscape, that has a mixture of higher water using plants.

Drought

Sometimes this tree is put in a part of the landscape surrounded by rock and water delivered from drip emitters. Rock surrounding this tree is not a good idea. As the tree gets bigger it needs more water. If more emitters are not added or more water provided during summer months it can become droughty and you will see dieback of limbs.

Smooth bark of some trees can lead to sunscald. The orange discoloration on the trunk is light sunscald. It helps if ash is not planted in rock.

Sunscald and borers

The bark on the tree when it is young is fairly thin so it doesn’t do well with intense sunlight on the trunk for long periods of time. It can get sunburned fairly easily when in west or south exposures of intense sunlight particularly surrounded by rock on the surface of the soil. This frequently leads to borer problems in the sunscald areas of the trunk. You will see dieback of limbs and a loosening of the bark on the trunk on the West or South sides of the trunk. The area under this loosening is dead due to intense sunlight (sunscald) and this is wear the borers are typically seen. Bayer helps but the real problem is its location in the landscape.

This is sunscald (sunburn) on the trunk of an ash tree. Most likely the trunk is dead on that side where sunscald occurs. This damage is thought to attract borers like the flatheaded apple tree borer which attacks many different plants.

Ash  decline

This is a disease that is common on many ash trees including Raywood. The damage resembles drought because the disease plugs the vessels inside the tree that carry water. The limbs begin dying and the tree dies a slow death over years. It is best to remove it if this is the case.

What to do? 

Look for damage to the trunk from sunscald and borers. If you see it then this could be the problem or part of a problem. Make sure the tree is getting enough water when it is watered. At 23 years old it should be getting 30 to 50 gallons each time it is watered. You can supplement water given to it by putting other plants that require water near it so they can share water. If you don’t see any improvement in the tree by giving it more water and you find no borers then it probably has ash decline and consider removing it.

The link below is accurate info on this tree. Other info could be sales hype.

Causes of Small Peach Fruit on Young Tree

Q. These are my sorry peaches harvested last Saturday. This is their third year, and they seem to develop to only this size. We fertilize them twice a year with vegetable spikes, and our in-ground system has Dr Bensons added 5 times per year. Any suggestions?

A. Age of the Tree

First of all, this is only a three-year-old tree! Give it a chance to grow up. The third year it is in the ground you should start expecting some fruit to be produced that you can eat. But not much. Most of the energy is going into making it bigger, not into production. 

Think of a young child. Would you want an eight-year-old daughter to have children?

Expect it to start into production this year to a very small degree and next year when it is really starting into production.

Thin the Fruit

This means remove fruit so that the remaining fruit gets larger. Think of it like this. If you are earning $20,000 a year, which is better for your family? Two children or 12 children? The answer is obvious.If you remove some of the fruit from the tree, the remaining fruit will get more of the water, nutrients and minerals sent from the leaves and the roots. This means the remaining fruit gets a larger share of what the tree can produce. Remove fruit so that there is the distance of a fist between the fruit. Do not grow them in clusters but space them along the branches in production. This may mean you could remove two thirds of all the fruit on a branch. Do this when the fruit is about the size of a thumbnail.

Peaches before thinning

Peaches after thinning

Removal of fruit depends on its purpose after harvest and the variety. Do you want large fruit so that you have bragging rights or smaller fruit. If it's for canning, sometimes large fruit is not the best idea but medium-sized is better. If it's going to fresh market for eating then larger peach size is usually better. The more fruit removed, the larger will be the remaining fruit.

Watering

To reach their maximum size, don't allow the soil to dry while fruit is developing its size. This means even amounts of soil moisture all the time it's producing fruit.. A layer of 4 to 6 inches of woodchips helps to retain soil moisture and produces larger fruit. 

4 to 6 inches of woodchip mulch helps conserve water and makes larger fruit. Don't surround fruit trees with rock.

Fertilizer

Fertilizer alone will not make larger fruit. But if fertilizer is lacking it will affect fruit size.Fertilize at least once during the year of production. The best time is just before flowering.

Fertilizer can be applied in many forms including compost, granular fertilizer and fertilizer stakes. Here fertilizer stakes are driven into the ground with a hammer near the drip emitters.

Pruning

Pruning peaches and nectarines is different from pruning most other tree fruit. Fruit is produced laterally or along the edges of last year's growth. You want about 18 – 24 inches of new growth produced each year. Half of all of this growth is removed during pruning. Leave too much last year's growth and sending becomes a nightmare. Remove too much of last year's growth and food production will be small but they remaining fruit large. This is something you have to play with until you get it right. It will vary with each of the different varieties.

Six-year-old Peach tree showing its open center form after pruning. Fruit will be produced on the reddish growth from last year. This growth should be distributed throughout the canopy and be about 18 – 24 inches long. The next step after flowering is fruit thinning when fruit is thumbnail sized.

What Are Polymorphic Leaves?

Q. My daughter in Illinois asked me about this. Two different kinds of leaves growing on the same tree.

This picture was sent to me but I think it was borrowed from this blog,https://earthshinenaturewatch.blogspot.com/2015/08/polymorphic-leaves.html 

A.Academically these are called polymorphic leaves, two different shapes of leaves growing on the same plant. Plants are much more variable than animals. Here is a good example.

You can read an at academic treatment about Polymorphism by following the link here.

The word polymorphism is a common concept in biology. The term polymorphic is applied to animals as well as plants when there are different forms of the same animal or plant part. So in the case of polymorphism in trees we use the term "polymorphic leaves", or "polymorphic flowers" for instance because these are found on the same plant. Polymorphic leaves are very common on mulberries where this photo is from but it can also be found in the East Coast of the United States on Sassafras.

It can be applied to biochemicals and the term also used in genetics.
https://www.actahort.org/books/1173/1173_9.htm

We can only guess why there are different forms of leaves in mulberry. In some herbs, polymorphism is thought to be related to soil moisture content.
http://forestandrange.org/new_wetlands/plant_adaptations_polymorphic.htm

In Red and white mulberries, some people think it has to do with access to light were full leaves are produced in the early and leaves with lobes or cuts in them are produced later in the sunlight above shade leaves. It is thought that this is an evolutionary adaptation that allows more light to reach the lower leaves. Of course these are just guesses about why plants do the things they do. Otherwise, just enjoy their diversity.

So if you want to sound educated and knowledgeable throw around the term "polymorphic" so people will be impressed.

Pomegranate Planting and Management Presentation in Logandale, Nevada

When: Saturday, October 13 from 9 am to 1 pm.
Where: 1897 North Moapa Valley Blvd., Logandale, Nevada

Space is limited and so are tickets due to the size of the classroom..

My presentation is in conjunction with the the University of Nevada Cooperative Extension and the 23rd annual Pomegranate Festival , this year on November 2 and 3, and held each year.

For more information call Nevada Cooperative Extension in Logandale, Nevada, at 702-397-2604, Extension 0. Or email walkerd@unce.unr.edu

Free tickets for the event are available at Eventbrite but space is limited.

Robert Ll. Morris is a Horticulturist and Associate Professor Emeritus from the University of Nevada who has been working with food and water issues in the arid West and around the world for the past 40 years. Robert spearheaded the University Orchard in North Las Vegas growing a wide range of fruits, vegetables and herbs and pioneered the marketing of locally grown food by small-scale producers in the Las Vegas Valley. He is co-author of two publications published by the University of California and CAST (Council for Agricultural Science and Technology), authored over 35 research articles, over 1,000 trade journal articles, a regular columnist with the Las Vegas Review Journal newspaper, Consulting Editor for HortScience, a flagship publication for the American Society for Horticultural Science. Visit his blog at Xtremehorticulture.blogspot.com. Questions about the class can be directed to his email at Extremehort@aol.com. 

Sudden Death of Established Fan Palms

Q. I have 19 mature, healthy Mexican fan palms pruned every year after flowering. This year they were pruned on June 13 but after three weeks one suddenly died, and another died two weeks later. I used the same pruning crew for 5 years with no problems. I removed about 250 square feet of turf from in front of the trees last year with no other significant changes to their irrigation or fertilization regimen. 

A. They died because the central bud at the top of the tree died. I can’t tell you exactly the reason why they died without climbing to the top, but I can give you some possibilities. Perhaps you can sort it out from there.

            I don’t think this is an irrigation issue because it happened too rapidly. It is most likely a disease problem. I would guess it is either from using unsanitary pruning tools or too many palm fronds were removed.

Sanitation a Problem

            Pruning tools must be sanitized to prevent the transmission of disease from one tree to another. Diseases are passed from tree to tree or even limb to limb by using unsanitary tools. At a bare minimum, pruning tools should be sanitized between job sites. Ideally, they should be sanitized between trees, particularly when pruning “sick” trees.

70% ethyl alcohol is probably the best sanitizers but a good cleanser will work

            I like to ask, “Would you let a doctor use a needle or scalpel just used on another patient?” Pruning plants is similar. Disease transmission is less likely between plants that are not similar but when plants are similar, all palms for instance, more care should be used.

            Sanitation of pruning tools can be simple; from wiping the tools clean and applying alcohol for Pine Sol or even heating the blade with a Bic butane lighter.

Too Many Fronds Removed

            The second possibility is damage to the central bud by removing too many fronds protecting it. The central bud of a palm tree is located at the very top of the trunk. It is surrounded by palm fronds that emerged from the bud earlier in the season.

Removing too many fronds can leave the central bud exposed to intense sunlight and brutal wind, the bud dies and the tree collapses.

            The newest fronds are clustered around the bud while older fronds are lower and removed as they become brown or drop below horizontal. Older fronds provide no protection to the bud. Horticulturists all agree that excessive removal of palm fronds can lead to palm problems.

            Excessive removal occurs when fronds are removed that previously played a role in shading it from intense sunlight or protection from other types of damage. If too many fronds are removed, protection of the bud is jeopardized.

Too many fronds removed? Duh!!!! This is exaggerated but it was done! Leave a half-moon of fronds when you are done.

            How many should remain after pruning? Enough to protect the bud and provide energy through the leaves for vigorous new growth. Remaining fronds should occupy an upside down half-circle or 180°. 

Whats Causing Warts on Limbs of My Pine Tree?

Q. I have several Mondale pine trees and recently noticed round bumps on some branches. I love these big trees, so I really hope I don’t have to take them out.  I deep water once a week in summer and once a month in winter and they have done very well so far.

Bumps or warts on limbs of Eldarica pine

A. I don’t recognize the problem to your trees as something serious. These rounded bumps are probably resin pockets in the limb. It could be caused by a nonlethal virus disease. It is also possible it could be a physical reaction to weed killers applied nearby.

            Keep an eye on the tree and its growth. Apply enough water and fertilizer to get eight inches of new growth each year on older trees; 12 – 18 inches on younger trees. If the tree is doing well on your watering schedule, then keep it. Just make sure enough water is applied for it to drain 24 inches into the soil.

New growth on pine are called "candles" and you can see why. This new growth should be strong and vigorous in healthy trees.

            Water should be applied to at least half the area under its canopy. Add an extra irrigation when temperatures are above 110 F and windy.

            One application of fertilizer in the spring of each year should be enough. When it is hot and windy (like over 110F), give it an extra deep watering. If the tree canopy is thinning the tree may need water or fertilizer or both.

Whats Causing Top Dieback in Mulberry?

Q. What is causing the “big hurt” on mulberry trees? There was considerable damage to most trees in recent years. What caused so many dead branches this and last year?

Sooty canker disease 

A. Mulberries are solid performers in the hot desert if they get enough water and are pruned properly. I am not endorsing their planting; they use a lot of water and the male trees release large amounts of allergenic pollen, a huge health problem for many residents.

Battle of the Sexes

            The female trees are not “outlawed” in southern Nevada. The male, or fruitless mulberries, are. Female trees can be planted and will produce fruit without male trees because of large amount of airborne pollen produced every year from existing male trees.

Bowl of purple and white mulberry fruit in Tajikistan. Many countries I visited call the fruit "toots".

Sooty Canker Disease

            We see an increasing number of mulberries with dead branches in the tops of the trees. Most of this is “sooty canker” disease. This fungal disease spreads from tree to tree on poorly sanitized pruning equipment, birds and insects.

Sooty canker disease on ash. Looks the same on mulberry.

            It also infects other trees besides mulberry including ash, poplar, apple and many others. Frequently, the health of infected trees was “compromised” in some way making them susceptible to an otherwise weak pathogen.

            What compromises the immunity of otherwise vigorous trees growing the desert? Usually its water; a lack of it causing them to be stressed. The disease organism is transported to this weakened tree on pruning tools, or perhaps by birds or insects. This pathogen enters the tree through open wounds caused by pruning equipment, fresh openings left by dropping leaves, or through the flowers.

Consider this scenario: 

Sanitize pruning equipment before pruning

a landscape converts from large, established trees and lawns to a desert landscape; the lawn is removed and drip irrigation is installed; large established trees do not get enough water and limbs begin dying; landscapers remove limbs with unsanitary tools; the trees become infected; disease spreads because the tree’s health is compromised due to a lack of water.

            Simple solution? Sanitize pruning equipment.

Considering Growing Tipu in the Eastern Mojave Desert?

Tipu tree growing in Las Vegas. Will we get winter temps below 25F? Plant this tree and you are betting we wont.

Q. I have been wanting to plant a tipuana tree since I saw one in person (those pinnate leaves are gorgeous!) and I love the idea of a wide canopy.  You mentioned in a December 2013 blog that here the potential for damage from the roots would not be as concerning in Las Vegas as in other places as long as it was planted “several feet away from foundations, etc.” The location where I would like to plant is between the pool and the block wall.  The wall and the pool are separated by 19 feet.  Would planting 4 feet from the wall and 15 feet from the pool be reasonably safe? I have citrus, duranta repens, and some other cold sensitive plants that I dress in old school Christmas lights and wrap in frost cloth, so I understand it will take extra work to protect from the cold.  What do you think of my chances for success? I do love the leaves, though. Maybe I can talk myself into a purple robe locust instead. 

A.  Just to be a little more clear than the section you read in my article. I am not a big fan of this tree but it has been pushed for planting in the Las Vegas area by a local nursery. You should read some of the comments from Arizona State University (Mesa, AZ) about its use in Phoenix. 

Winter dieback of tipu in Las Vegas.

Comments about Tipu tree from ASU

I am always seeing the downside of plants because I get hit with problems all the time. The Purple Robe Locust is a good tree. It is also not desert adapted but it can handle the low temperatures with no problems.

But it should be grown with woodchips as a mulch and use compost mixed in the planting soil at planting time. It is a medium water user and it will get about 35 feet tall and oval to round in shape. It is not a fast grower, not slow either but about 12 to 18 inches per year if you fertilize and water it well.

Avoid putting it in very hot locations with lots of direct sunlight beating down on its trunk and limbs. Keep it full and keep the lower limbs shading the trunk as long as possible. Surround it with lots of other plants that like a similar irrigation.

Texas Mountain Laurel in Las Vegas. Can have a spring insect problem but easily controlled.

Consider Texas Mountain Laurel, Texas Olive, Desert Museum palo verde, Red Push Pistache, etc. Even ornamental pear aka Callery pear. A better fit for our climate. All trees have problems but these would have fewer tree life threatening problems.

Use Houseplant Moisture Meter to Know When to Irrigate

Q. I am using an inexpensive soil meter to help me judge went to water again. I redid my landscape to include cacti, ocotillo, agaves and other types of desert plants. Do I let my meter peg to 1 before watering again or is 2 to 3 okay?

A. I have promoted the use of moisture meters for helping gardeners “get a handle” on when to water plants. For non-desert plants, like many of our trees and shrubs, let the soil moisture drop to about 50 -60 % before watering again. If the meter is divided into 10 equal units, this would be about “6” on the meter’s scale.

The scales are relatively accurate

            Desert plants that are not cacti, like Mesquite, Palo Verde, Acacia and leafy succulents, the meter can drop a little bit lower than this before watering; about 40-50% or about “5” on the same scale.

Another example of reading soil moisture with an inexpensive moisture meter..

            Cacti is in a category by itself. I think you are about right. Let the soil moisture drop to between “2-3” before watering again. Because cacti store water inside their modified stems and leaves, they give a visual indicator when their water is running out; the outside shrivels. That is a dead giveaway it’s time to water.

A third example of using a soil moisture meter for gauging when to water again.

            When I am irrigating non-desert plants like fruit trees in a soil that is new to me, I take three readings in different locations around the tree and use the average. I don’t let any readings drop below “5” and I will water if the average is about “6”. After I get the “rhythm” of seasonal water use, I seldom need it after that.

Soil moisture meters I use alot for approximating soil moisture for irrigation
Reotemp Soil Moisture Meter Link
Lincoln soil moisture meter but the price has jumped up too high for me recently

Probes that are longer are more versatile

            The other thing I do is push the probe of the meter into the soil slowly. I want to measure soil moisture near the surface of the soil and watch how it increases with depth. This technique helps me understand how fast water is leaving the soil.

When to Water

            There are two questions you need to answer when watering: when to water and how much to apply. Soil moisture meters help mostly with the “when” to water.

            I judge how much water to apply by pushing a thin metal rod, like 3/8 inch rebar, into the soil. It slips into the soil easily when it’s wet. For trees and shrubs, apply enough water to penetrate 18 to 24 inches deep. For lawns, flowerbeds and vegetable gardens, 12 inches deep. Two foot tall shrubs, vines and groundcovers, 12 to 18 inches deep.

            These are inexpensive meters andnot meant to last forever when pushed into our soils. Once you get the “feel” for when, you won’t need it often. Just occasionally when you aren’t sure.

Steps

1.         Insert it in the soil slowly. Get moisture readings as you slowly insert it into the soil. This gives you an idea how the soil is drying out with depth. Newly planted seeds, trees, shrubs, need water frequently but only a little. As they grow they need water less often (deeper) but more of it.

2.         Take three soil measurements in different locations. Insert it between emitters (if that is what you have). Otherwise insert it anywhere, randomly, above the roots.

3.         Observe your moisture meter readings as you slowly insert it and at the depth of the roots. For flowers and grass, this will be about (slowly) 6 inches deep. Remember that plant roots use water using the 40-30-20-10 rule…40% of the water they use is in the upper quarter of their rooting depth, 30% from the second quarter, 20% from the third quarter and 10% from the bottom quarter. If the plants are grass, flowers or vegetables the roots are divided into upper quarter (zero to three inches deep), second quarter (3-6 inches deep) third quarter (6-nine inches deep) and bottom quarter (9-12 inches deep). Tree roots are 18 to 24 inches deep so adjust your “quarters” to this depth. This is why it is important to push it into the soil slowly.

4.         Take three readings like this. Average them. Use this value to determine when to water.

9-10    =   Wet. Don’t water.

7-8    =   Moist. Don't water.
5-6    =  Water.
3-4    =  Water desert plants

1-3    =  Dry. Your plant is dead unless it’s a cactus. Buy a new plant.

How much to water? 

Look at the size of the plant. Can you plant it in a 1 gallon container? Water it ½ gallon. Can you plant it in a two gallon container? Water it with one gallon of water. Can you plant it in a 5 gallon bucket? Water it with 2 ½ gallons (round it to 3 gallons). Got the idea?

3/8 inch diameter rebar used for measuring irrigation depth inexpensively

Trees and large shrubs are more difficult to judge the container. Space emitters every 18 to 24 inches apart under AT LEAST half of its canopy. Water long enough for the water to drain 18 in deep. The easiest way to judge this is using a 3/8 in rebar, pointed or sharpened (flat if you cant sharpen it) and push it into the soil after you water. It will push easily to the same depth of the water.