Sweet Bay Tree May Struggle During High Summer Temperatures

Q. Sweet Bay trees (Laurus nobilis) border our property on all 4 sides totaling about 35.  They are now about 15 feet tall with 5" trunks.  We have lost trees in the past from under watering.  How many gallons of water should each of these trees receive on the winter watering day?

Bay Laurel leaves

A. You may know Dr. Devitt from UNLV and I published research articles on water use in the past in numerous research journals. Plants are extremely variable in water use depending on their type, size, where they are planted, and how they are grown. We published a book on irrigation of trees, and it is available on Amazon.

You will get many different responses on plant water use depending on who you talk to. However, we do know this: the more trees present, the more water is needed and the bigger the tree is, typically the more water it uses. Conversely the way to reduce water use is to plant fewer plants, use open spaces in creative ways that don’t require water and use desert trees that mature into a smaller size.

The picture above shows a mesquite tree with a 20 foot diameter canopy (left) and an apple tree with a 20 foot diameter canopy (right). The mesquite annual water use would be about twice that amount (4600 gallons each year) and the apple about twice that amount (13,600 gallons each year) as well. The water savings is in how often water is applied (frequency of irrigation). They both need water applied to wet their roots to the same depth (the minutes are the same in the same soil) but the mesquite water is applied less often. The soil become drier between irrigations. That means they should be on separate irrigation valves (hydrozone). 
https://leafnetworkaz.org/Water-Resource-Strategy

To roughly estimate tree water use, assume trees are divided into three categories; very low water use (e.g., foothills palo verde @ 0 to 2 feet of water), medium water use (e.g., vitex and bay laurel @ 2 to 4), and high-water use (e.g., mulberry and poplars @ 4 to 6). Moderate water use means it uses from 2 to 4 feet of water (applied under its canopy) each very year. FYI, tall fescue lawns use between 7 to 8 feet of water in this location and soil. It has shallow roots and NOT a desert plant to look good.

I recommend applying this amount of water to at least half the area under its canopy every year. (The reason I say half of that area is because I am realistic when it comes to home watering and know that people will not apply water to a the 20 foot diameter area needed by trees with a 20 foot diameter canopy!) When water is applied each time, apply it so that the soil becomes wet to a depth of 18 to 24 inches. If water is applied to half the area under a bay laurel tree (20 feet tall) so that half of this area is wet, one tree will require from 9000 to 10000 gallons of water each year. The same area covered by a lawn requires about double that.

Desert trees like the mesquite will be watered again just before the leaves will drop or as the tree canopy begins to thin out. That's your signal to water! During summer heat with desert trees like mesquite that might be once a week or once every two weeks. During the winter that might be once a month or once every two months. The deep roots will take over water uptake when the upper soil gets too dry.

Minimize Water Use and Increase Comfort in Desert Landscapes

Minimize the total number of big plants in a landscape

This tree is out of scale with the house. It doesn't need to be that big. It only needs to shade the walls and windows. The bigger the tree, the more water it uses.

Water is a scarce resource in the desert. Its price will always increase. Lowering landscape temperatures and irrigation go hand in hand. If water is used wisely, temperatures will decrease where water is applied. Plants always require water when growing in the desert. Wherever plants are planted in the landscape, water is needed. Large mature sized plants require more and more water as they grow bigger and bigger.

Do three things to your landscape to become efficient in its water use; preserve only the plants that provide you and your home the most cooling and pleasure, improve the irrigation system, and learn how to water. The last one, “learn how to water”, should be first. Learning how to water landscape plants enlightens the others.

Shade the south and west sides, walls and windows of your home and outside sitting areas

Create sitting areas with shade from plants or nonplants. Nonplants don't use water.

This type of irrigation creates “oasis landscapes”, perfect for the desert. Plan to apply the most water to “oasis” areas. Trees and shrubs provide the most cooling for homes and sitting areas. There is nothing wrong with open areas, but they will be hotter. Make these open areas interesting to look at.

Shade doesn’t have to come from plants

Shade also comes from man-made structures. Concrete and steel structures are the best choices for desert climates and don’t use water. There is nothing wrong with artwork in landscapes. Consider man-made structures in combination with vines or smaller plants instead of trees. Small plants use less water than big plants. Where are large plants found in the desert?

Concrete and steel structures are more durable in the desert.

Drip irrigation is among the most efficient ways of irrigating plants

But if you don’t know how to use it, it’s no better than flooding the landscape with water. Plants growing above 3 feet tall should be watered less frequently. Roots of tall plants will find water applied to the smaller plants and adjust their root growth to where water is applied in these areas.

Bubbler and basin irrigation can be just as efficient and easier to install for large trees as drip. Just keep the basins repaired and enlarged as the trees grow.

A well-designed irrigation system and the knowledge how to use it puts you in charge of watering rather than the landscape telling you when it needs water.

Every Landscape Architect Should Know This about Desert Soils

Desert soils have characteristics which make them unique among all the other types of soils. These characteristics encompass its chemistry, structure, biological activity and consequently how plants respond after planting. Desert soils are stable under a desert climate. Once manipulated they are no longer the same and impact management decisions long after landscapes have been installed.

Surface of typical sandy loam soil in the eastern Mojave Desert of Las Vegas, Nevada, with no organics in it

Rainfall and Desert Soils

Desert soils are characterized by the desert climate where they were formed and the rocks or geology that decomposed to form them. The dominant climate feature of deserts that impact soils the most is rainfall. Not total rainfall, but effective rainfall.

What’s the difference? Total rainfall is the amount of water that falls from the sky. This is measured using rain gauges. We hear it on the news. “Total rainfall yesterday was one quarter of an inch.” But that is not effective rainfall.

Effective rainfall is the amount of rain that actually enters the soil, stays in storage and supports plant growth. This can be far less than total rainfall. If total rainfall comes down slowly then a higher percentage is “effective”. If rain falls in a torrent, much of it runs off the surface and therefore a much smaller percentage is “effective”.

For deserts in general I have heard the magic number “40%” tossed around to convert total to effective rainfall. Personally, that sounds high to me for the Mojave Desert because the soils are much different than other deserts in North America. The primary reason they are different? The amount of plant material present. Why is there a different amount of plant material? Rainfall. Give the Mojave Desert more rainfall and the soils change.

Amount of Rainfall Dictates Number, Size and Type of Plants

The amount of rainfall dictates the size, number and the type of plants found in deserts. For example, compare the size, quantity and type of plants growing in the “lush” Sonoran Desert (with an average of ten plus inches of rainfall) versus the more barren Mojave Desert (four plus inches of rainfall). Most parts of the Sonoran Desert receives 150% or more water than the Mojave. More rainfall supports a greater number of plants and these plants tend to be larger.

Eastern Mojave Desert near Las Vegas, Nevada

By adding more water to desert soils through irrigation, the size, number and type of plants will or can be increased… artificially. Little else needs to be done to the soil than add water IF plants which originate from deserts are used. Let’s call these “desert plants”.

Desert Plants Better "Tolerate" Desert Soils

This doesn’t mean that desert plants don’t appreciate soil improvement but desert plants are better suited in “tolerating” the unimproved soil conditions of a raw desert soil. When propagating prickly pear cactus (nopal cactus) from pads in the Sonoran Desert of Mexico it is a common practice to amend the desert soil with manure at the time of planting. In a demonstration of growing these cacti from pads in the Mojave Desert with and without soil amendments I have witnessed a substantial improvement in growth when compost is added to the soil rather than applied to the surface after planting.

Desert Soils Change When Irrigated

When “effective rainfall” is increased artificially, desert soils change chemically, biologically and physically. Soils that were relatively unchanged for thousands of years, stabilized at around 2 inches of effective rainfall, now receive 50, 60 even 90 inches of effective rainfall. It’s silly to think nothing will change. As the saying goes, “Somethin’s gotta give.”

Unless a footer is constructed well, desert soils "settle" when irrigated as they change

Changes to the soil occur rapidly as a result of this much “effective rainfall”. Minerals in the soil that were stable, like gypsum or limestone, begin to solubilize quickly. Chemical changes occur. The pH of the soil begins to drop as plants grow and plant roots pump out carbon dioxide into the soil which dissolves in water to produce carbonic acid.

Roots of plants constantly die and regenerate providing food for microorganisms. As these microorganisms begin to colonize these “enriched” soils, they pump more acids into the soil. Changes in soil pH might be faster if a unit change was linear. Changes in pH are not linear. They are logarithmic. A change of one pH unit is similar to a one unit change in seismic activity on the Richter scale. A one-unit change equals a factor of 10.

Little Rainfall = High Salts

Desert soils commonly have an abundance of salts because of low rainfall. Salts are removed from soils by flushing them with water. Salinity of a soil drops as elevated amounts of “effective rainfall” wash these salts past the root zone of plants.

Salts move from the soil in the irrigation water as this water dissolves salts, wicks to new locations and evaporates

Artificial Desert Rainforest

Just as the “effective rainfall” of an irrigated urban landscape is not natural, the number and size of landscape plants installed in them is not “natural” or sustainable without this irrigation. Other “inputs” are needed to sustain this “artificial desert rainforest”. The type of inputs needed are dictated by the type of plants selected for a desert landscape. One of my favorite sayings is, “The further our landscapes drift from a true desert environment, the more time, energy and money is needed to sustain them.”

Mass Planting and Irrigation Create Fertilizer Demands

We know there are 16 or 17 nutrients that plants absolutely need to stay alive. Some of these like nitrogen, phosphorus, potassium, calcium, magnesium and sulfur are needed in large amounts. Others, considered minor elements, are needed in much smaller amounts. If the solubilized minerals in the soil don’t release nutrients fast enough to keep plants healthy, then additional fertilizers must be supplied to make up the difference.

Even though a soil can be rich in nutrients, plant demand for some nutrients may exceed the soils ability to supply them or supply them in the proper form. Some examples are the extra calcium needed by intensively grown turfgrass on sand based greens, calcium deficiency of apples and pears grown on soils full of lime (calcium) or iron deficiency induced by a high pH in soils with an abundance of iron.

Add Organics to Desert Soils

Desert soils typically have low levels of organic matter. Organic matter in soils result from the death and decomposition of life (plants, animals and other organisms) that lives in it or above it. Climates that have more rainfall support more life. Soils influenced by these climates consequently have more organic matter in them than soils which have evolved under a desert climate.

Climates that have little rainfall support less life. Since our hot deserts have little rainfall, native or raw desert soils are low in organic matter. The raw, untouched soil of the Mojave Desert contains less than 1% organic matter.

More Water = More Organics

Desert soils that evolved with irrigated agriculture contain an abundance of organic matter compared to the raw soils of the Mojave Desert. Levels of organic matter in “farmed” desert soils can reach 4 to 5%, a level approaching the rich grassland prairies of Nebraska and Kansas. Why? Because of the artificially applied “effective rainfall” used to grow crops. Water is life. Water applied to desert soils evoke change.

Building organic matter in soils takes time. Organic matter in soils builds rapidly in the hot, wet tropics. In the grassland prairies, at 20 to 30 inches per year, it can take decades. Since organic matter never increases in desert soils without irrigation it must be added “artificially” when it is needed.

Desert Landscapes: Are they Really?

So-called “desert landscapes” no longer consist of “desert plants”. Nurseries and landscapers sell landscapes that look good with no regard for a plant’s origin. Nondesert photinia and mockorange are planted on the same valve and grown alongside Baja Fairy Duster or Arizona Rosewood and mulched with rock. In three to five years, the organic matter used at the time of planting decomposes and the soil “mineralizes” (loses its organic matter). The soils collapse and lose their porosity and ability to drain. Soil pH begins to drift upward. Biological activity declines. The non-desert Photinia and Mockorange begin yellowing and scorch while the more tolerant desert plants continue growing and appear healthy.

More Plants = More Landscape Inputs

The primary reason for these types of landscape failures is the combination non-desert plants with desert plants and managing this landscape as if it were a “desert landscape”.

I prefer the concept promoted by Dr. Warren Jones when he was with the University of Arizona – Mini Oasis. This type of desert landscape design grouped plants with similar needs together. Plants that grew well under rock mulch were grouped together and watered and managed similarly. Higher water use plants, many times non-desert plants, that benefited from higher levels of soil organic matter and wood chip mulch were grouped together. This concentrated plants which required more time, energy and money in one location, usually close to where people congregated.

 “The further our landscapes drift from a true desert environment, the more time, energy and money is needed to sustain them.”

Plant Recommendations Colorful, Fragrant, Heat Tolerant

Q. I am fairly new to the Las Vegas area and have a 23' x 3' area on the south side by a cement wall that gets some shade. I'd like to plant some type of bushes that are colorful, fragrant, heat and drought tolerant, need minimal upkeep and will grow approximately 6-8'. I have enough oleander.  Any suggestions?

A. I will assume from your email you want plants that stay about 3' wide, low maintenance, evergreen, and will accept some sun.  Flowers and fragrance would be preferred.  I see you want 6-8' tall   The plants listed below all stay around 3' wide.

These are all medium water use plants that grow about 3' x 3':

Dwarf Bottlebrush Callistemon 'Nana'

Dwarf Youpon Holly Ilex vomitoria 'Nana'

Gulf Stream or Moon Bay Nandina Nandina 'Gulf stream' or Nandina 'Moon Bay'

Box-Leaf Euonymus Euonymus microphylla

Low water use plants that grow about 3' x 3':

Blue Texas Ranger Leucopyllum zygopyllum

Brittlebush Encilia (2 varities available)

Autumn Sage Salvia greggii

Taller growing plants to consider with some trimming to stay 3' wide:

Heavenly Bamboo Nandina domestica

Dwarf Xylosma Xylosma c. 'Compacta'

Baja Fairy Duster Calliandra californica (deciduous)

Classic Myrtle Myrtle communis

A good source for plant information is snwa.com under 'landscapes' and then 'plant search'.   You could look up plants above and decide which are best for you.

Hope this helps.  Get back to me with any further comments or concerns.

Andrea Meckley, CH

Blond Ambition Ornamental Grass Good for Las Vegas Landscapes

Fall Or Winter Head Cold or Allergies? Shoestring Acacia.

Shoestring Acacia is in bloom right now and has been credited with allergy problems. In fact, they will bloom through most of the winter.

Shoestring Acacia flowers in Bloom in January

Shoestring Acacia can grow up to 40 feet tall quite rapidly and it is relatively upright so it can be useful in more narrow locations and in scale with two-story homes and commercial buildings.They are good selection for desert landscapes but allergies might be a problem.

 

Shoestring Acacia with a fairly wide form.

It is propagated from seed so there is a lot of genetic variability which means you can have narrow ones and you can have wider ones. If you are picking one that is intended for a narrow area, pick one that has a narrow habit to begin with in the nursery. Chances are if it is narrow in the container it is more likely to be narrow when it is older. If you pick one that is not so narrow when it is small, you do run the chance of having a fairly wide Shoestring Acacia.

 

Shoestring Acacia, narrow form. This tree is started from seed so there is a lot of variation in the trees. Pick one that is narrow to begin with and hopefully it will stay narrow if that is what you want. If you want one that's wide, then pick a form that's wide in the nursery.

It hails from Australia which, like so many trees from Australia, blooms during the fall or winter months rather than spring and summer. It is popular here in the desert Southwest and some people consider that it might be over planted.  There are complaints from people that it is messy and the leaves, because they are long and narrow, are difficult to clean up. Whatever you do, don't cut the top off. Trees that are pruned like this are ruined for life.

Shoestring Acacia topped at commercial planting North Decatur and CC 215

Small Front Yard Tree Not Messy

Q. I want to plant a tree in my front yard where it gets southern exposure sun and space is approximately 9 feet from house where it will be planted.  I want something that does not get over approximately 20 ft. at maturity, does not drop fruit, seed pods or anything messy, and is drought tolerant.  I was considering a Western/Mexican redbud, Hawthorne, Raywood Ash.  What do you know of these trees?  Do you have any better recommendations based on my needs?

A. Here are a few notes on the trees you mentioned from Andrea Meckley:

Western Redbud - litter form leaves in the fall (plant is deciduous) and spring flowers  Multi-trunked so not a good shade tree.  15' wide x 13' high at maturity meets goals.

Hawthorn - I assume you refer to "Majestic Beauty' Hawthorn Patio tree-Evergreen with little leaf drop and April flowers that are not much of problem.  Prefers morning sun, not southern exposure.  Matures at 20'h x 8'w although I have not seen much larger than about 10' high in the Las Vegas area.

Raywood Ash - Leaf litter in late winter because tree is deciduous.  Matures at 30' h x 20' w.

Here are a couple of trees to look at with your requirements.  

With the information you gave, the Mulga Acacia (Acacia aneura) sounds like the one I would suggest.

Mulga Acacia - Evergreen with small spring flowers are not a big litter problem.  Matures at 20'h x 15'w.  Can be a shade tree with a ball head or lower branches kept on for more shade.  Hardy.   Considered 'bulletproof'  on the Southern Nevada Regional Coalition Plant List. 

Smoke Tree - Leaf debris (deciduous) in late fall.  Matures at 15' x 15'. Multi stemmed, so leave natural for more shade or prune for tree form.

From Andrea Meckley

Eliminating Lawn Can Lead to Problems for Established Trees

Q. I have a beautiful Loquat tree where the leaves have suddenly started to turn yellow and fell off.   Most of the fruit has also fallen off. The tree was located in the middle of grass. I had the landscape converted to desert rock in September. At the same time watering schedule was changed. I suspect it is being under watered. But before I increase it I want to ask if the cold winter we had here could have caused this yellowing.

A. Thanks for the pictures. It is probably not the cold. In a lawn situation the roots go everywhere and anywhere and usually spread to about 1½ to 2 times its height away from the trunk.

Loquat with rock mulch applied after growing in a lawn for a few years. In many cases the drip emitters do not
apply the water in the same places as lawn irrigation and the plant roots of established trees and shrubs die back.
This results in leaf drop and eventual die back of the limbs of established trees and shrubs.

            In drip irrigation we usually place the emitters a foot or so from the trunk. This bypasses about 80% of the root system it created when growing under a lawn.

            So, yes, it probably is drought but perhaps not because you are not delivering enough water. It is more likely that most of the tree roots are not receiving water. You can place emitters over a greater area under the canopy of the tree. But I would also reduce the size of the root system.

            Try root pruning the tree to reduce the size of the root system so it is closer to the emitters. Keep tree roots contained in the area directly under the canopy. Wet the soil thoroughly under the canopy and vertically slice the roots in a circle all around the tree at the edge of the canopy. This can be done with a sharpened spade.

Leaf drop of established loquat due to replacement of lawn with rock mulch and drip irrigation.

            At the same time, thin the canopy by removing wood. This reduces the tree’s demand for water. A tree that size will probably require 20 to 30 gallons each time you water. With the lawn now gone, the tree will actually use more water since the cooling capacity of the lawn has been removed.

Fertilizer Formula for Keeping Crepe Myrtle Healthy in Desert Landscape

Q. We have a crape myrtle tree in our southwest back yard. It gets plenty of water and I fertilized it last month with some Miracle Grow flowering fertilizer. At the time there were some burned edges on some of the leaves and some yellowing. Now it is really burned on the edges of all of the leaves with yellowing. HELP!

Crape myrtle growing at Center for Urban
Horticulture for 20 Years on Formula
Mentioned Here

A. A couple of things on your crape myrtle. I have kept crape myrtle growing in raw desert soil in good shape for 20 years at the Center for Urban Horticulture and Water Conservation in North Las Vegas. I used a combination of a general purpose tree and shrub fertilizer (16-16-16) plus an iron application combined with foliar sprays of Miracle Gro.

            I don’t really endorse products but Miracle Gro is the one I used and have found to work just fine. You could just as easily use a different good quality foliar fertilizer for flowering woody plants. I apply the granular 16-16-16 in late January or early February using about 2 lbs. of fertilizer applied to the surface of the soil and watered into the roots without it washing against the trunk.

            You can make some shallow holes in multiple places under the canopy and water it in thoroughly. At the same time, I also apply an iron chelate, iron EDDHA at the rate of a tablespoon or two scattered in the same holes and watered in so that none of it remains on the soil surface. It is light sensitive.

            After about one month of new growth I then foliar fertilize the tree with a Miracle Gro spray or comparable product. I do both of these annually. You can do the same thing (except for the iron) by using a fairly large quantity of good quality compost annually. My guess is you either are missing the iron application, watering too often or not watering deeply when you do water.

Loquat Turning Brown in Rock Mulch

Andy's loquat

Q. I planted a five gallon loquat in my front yard three months ago in April .  It seemed to be taking just fine at first.   A few weeks ago I noticed that the older leaves were beginning to turn brown and  the newer leaves seem to be shriveling up.  When I purchased it I was told it was OK to plant in full sun.    

During this heat I drip water it every two days.  I estimate it receives about six gallons per watering.   I check the soil regularly to make sure the soil is not drying out.  Any thoughts.

Attached are some photographs. 

-Andy

Closeup of Andy's loquat

A. Andy,

As you found out Loquat will not like it in rock mulch in full sun. It will do all right in full sun in a mixed planting with lots of other greenery around but it will actually do better in a more protected location.

If you can put it in an area with protection from late afternoon sun and surround by other plants it will perform better. Loquat does tend to get borers easily if heat stressed.

Joshua Tree and Other Agaves Acceptable for Pool Area

Young Joshua tree in desert landscape

Q. A visitor has told us that we need to remove our Joshua Tree and Agaves from around our swimming pool. The Joshua Tree is about 4’ from the edge of the pool and the Agaves are about 2’ from the edge. Do we have a problem with these plants trying to get into the pool water?

A. I tried to think of reasons why this person would tell you this and I cannot think of any.

I don't agree. These are very good choices close to a pool area. What is nice about plants such as these is that you can direct their root system with the location of your water supply. I suppose there could be cracks in the pool that would allow for leaks.

However, most plants go after water which is the cleanest. If you apply drip irrigation to the sides of the plants away from the pool this will encourage their roots to grow in this direction.

Pool water is not good water for most plants and if they have a chance to take up better water they will. So keep your drip emitters or your sources of clean water on the side of the plants away from the pool. These types of plants survive on infrequent rain water so their roots are typically shallow and very efficient at scavenging for water close to the soil surface.

 

American agave

Water them with shallow irrigations, perhaps no more than a foot deep and don't do it very often. In Midsummer if you want to encourage growth water them every two to four weeks. If you want them to slow down, water them less often. Watch carefully for agave weevil attacking and killing primarily agaves and in particular American agave. I have posted information on their control in this blog. You can search for it by entering agave weevil in the search box.

Putting Rock Mulch on Top of Composted Soil/Wood Mulch for Fruit Trees

Q. In my backyard in 2010 I planted a semi-dwarf Early Elberta Peach tree and a Katy Apricot.  I hand-watered them and left their tree wells uncovered until I completed the irrigation system around April 2011.  Now each tree has drip emitters. I put a thick layer of Dr. Q's Pay Dirt potting soil on top of each tree well and then covered the potting soil over with a layer of the ruby red stone that I have throughout the floor of my backyard.  Both trees are doing very well and I want to be sure to do everything I can for their long-term health.

            Per your View article, should I move the red stone back off the top of the tree wells to a radius of 6 feet away from each tree, and then cover each tree well with a layer of wood mulch instead?

 A. One soil problem we have when growing fruit trees in our desert is the small amount of organic matter in our soils. This miniscule amount of organic matter is not enough for nearly all plants including so-called desert plants.

            Fruit trees, and nearly all other plants, perform much better in our soils if organic matter (compost preferably) is added to the soil surrounding the roots. I hope that you added a lot of amendments to the soil at the time of planting, not just the surface.

            I have compared two application methods when compost is applied to fruit trees: mixing it only to the soil at the time of planting and adding it only to the soil surface after planting. Adding it to the soil, not just the soil surface, dramatically improves plant growth in our desert soils.

            The best soil amendments to use to use when increasing organic matter in our soils are homemade composts. Commercially made composts, available in bags or bulk and extremely variable in quality, would be next. The good ones (there are good ones out there now thanks to the explosion in organic gardening) are expensive. The cost of enough good quality compost, added to the hole at planting time, in some cases might rival the cost of the plant itself.

            If trees are planted in amended soils and then the soil surface covered with rock, over time, the organic matter in the soil is “used up” so to speak by soil microorganisms. When the majority has been used up, we say the soil has become “mineralized”. Without addition of organic matter to the soil surface every two to three years, the soil slowly reverts back to its previous desert condition.

            From my observations of fruit trees and nondesert landscape plants growing in our desert soils amended only at the time of planting and mulched with rock only, the soil is typically “mineralized” by the fourth or fifth years. Cacti and desert plants are much more tolerant of mineralized soils but still grow better in amended soils.

            By placing wood mulch on the soil surface where the soil is wet, it slowly decomposes. Through its decomposition it adds organic matter to the soil. Through their decomposition, mulches add a lot of organic activity such as beneficial microorganisms and earthworms leading to improved plant health. Rock mulch cannot add organic matter and so in a few years none of the benefits of organic mulches will be present.

            I am guessing your trees will be fine for several years with rock mulch covering the soil surface. But what may happen in the fourth through the sixth years, as the soil becomes mineralized, is that they may begin to decline in health.  The trees may become more and more yellow, leading to leaf scorch, followed by branch dieback and insect attacks such as borers.

            Borers come into play due to a decline in tree health. Decreased plant health causes a thinning of the tree canopy leading to an increased amount of sunburn damage to the limbs. Sunburn damaged areas are the ideal locations for borers damage to occur.

            My concern would be how you might add organic matter to the wet soil surfaces as it decomposes. If you can do this then it will probably not be a problem.  It is best for the trees if you can put wood mulch in the wetted area under the trees. In the drier areas under the tree the wood mulch will not decompose.

Can Myers Lemon Do Well in Rock Mulch?

Q. I live in the far western area of the Las Vegas valley.  I have a good sized area covered with rock mulch. A flowering plum tree (soon to be removed) is struggling in this area. Can a Myer’s lemon tree do well in a rock mulch setting?

Loquat in rock mulch

A. I would not recommend it. It might do okay for a few years, maybe 3 to 5, and then it will start to take a dive. You will have much better luck if you can pull the rock away from fruit trees, including your flowering plum, perhaps 6 feet or so from the trunk and putting down wood mulch instead of rock.

            If you decide to plant some citrus, I would highly recommend adding a lot of compost to our desert soil at the time of planting. It is much more effective to mix it in the soil then it would be to try to add it to the soil after it has been planted.

Almost All Plants Like Wood Mulch - Even Desert Plants

Roses don't like rock mulch

Q. I heard it is best to move rock away from my shrubs and replace it with mulch.  What is your recommendation?

A. Rock can also be a “mulch” and we call it that in our desert landscapes; rock mulch. We have three categories of mulches; organic, inorganic and living. In the organic category are wood mulches. In the inorganic category we have rock mulches. All mulches are important but organic mulches, like wood mulch, give extra benefits to plants that rock mulches cannot.

            Our desert creates its own rock mulch and that’s why plants that originate from desert environments can “tolerate” rock mulches. It is not that they grow better in rock mulch but rather that they survive better in it.

            Nearly all plants grow better with organic mulch rather than rock mulch when grown in our desert soils. Plants like most of our fruit trees, roses, iris, lilies and those which are not true desert plants, perform better with wood mulch.

Mockorange yellowing in rock mulch

            Those that come from desert climates like mesquites, acacias, desert bird of paradise, agaves, cacti, etc. will tolerate rock mulch better than nondesert plants. But in most cases they still perform better surrounded by wood mulch.

            Newly planted trees and shrubs should have wood mulch kept away from them a distance of about one foot the first few years of their life. After that they usually tolerate wood mulch in contact with their trunk. This is because the wood mulch keeps the soil too moist and can cause the trunk to rot when they're young.

Winds Blew the Flowers Right Off My Peach Tree

Q. For the last two years in North Las Vegas heavy winds have come while my young peach tree was in bloom. Both years I wrapped it as best I could but the blooms were blown off the tree anyway. Do you have any good way to protect the tree during these windy times? You don't wrap your trees at the farm?

A. We don't wrap our trees and we are exposed to strong, cold winds from the northwest with recorded gusts of 70 mph. My guess is that the wind is channeling through that area which will increase its speed. I would suggest constructing a windbreak to protect that small area by diverting or slowing the wind. This can be made from fencing or evergreen plants.

fact sheet on windbreaks

            You do not need to stop the wind entirely but you can slow it down with a windbreak. Windbreaks should not be a 100% barrier to wind but allow about 20% of that wind to penetrate through it. Things like chain-link fences with PVC slats or woven materials placed along windward side of the fence will affect wind a distance of 5 to 8 times the height of the barrier.

Open publication - Free publishing - More wind damage

            Wind will increase its speed if it goes from a large area through a small area such as between homes or into backyards. This can be a problem if this channeled wind enters small areas where fruit trees and vegetable gardens are located.

            Be creative. See if you can design a windbreak into your existing landscape that can help modify that part of your yard and make it more enjoyable.

Ornamental or flowering plum leaves
with wind damage

Q. I put in a desert landscape with 2" of rock in the front yard with various bushes and 2 flowering plum trees. This probably was a mistake, as I read one of your articles which said that this type of tree is not suited for rock mulch. Anyway, my question is about watering the trees. I have a 28" diameter by 5" deep watering reservoir around each tree. There is a layer of bark mulch in the reservoir. Right now I water the trees twice a week filling the reservoir up twice at each watering.

This is purple leaf plum in a desert or rock landscape.
It will look good for about five years without much
attention. But after about five years it usually starts
with leaf scorch and may begin getting iron chlorosis

So far every summer around August some of the leaves partially dry out and turn brown. Is this caused by too much water or not enough? I water the bushes 3 times a week by drip system for 30 min per watering. They are all healthy and green. Also the bark on the trees are splitting in places and falling off. Do you think I will loose the trees at some point? Any advice will be greatly appreciated. I read all your colums in the RJ that you write. Lots of excellent advice there.

A. Flowering plums can handle the rock better because you aren’t really worried about a crop of fruit to eat. But the rock on top of the soil will aid in the depletion of organic matter and over time it will most likely turn the pinkish color that accompanies iron chlorosis in red leaved trees like the purple leaf plum. If not corrected that can lead to more of a decline in the tree opening it for dieback and insect/disease problems.

This is the purple leaf flowering plum when it has iron
chlorosis. Plants with green leaves will have their
leaves yellowing with green veins. In plants with purple
leaves the leaves will turn pink instead of yellow but
the veins will still be a darker color than the leaf blade

Bark mulch is not nearly as effective as plain old ugly mulch made from chipped landscape trees. Not many nutrients in bark, it decomposes slowly, and is all just about the same size so it doesn’t decompose as effectively as chipped wood mulch. Plus 28 inch diameter irrigation basin is not very big. As these trees get bigger they will need more water. Increase the basin to about six feet in diameter (three feet from the trunk) all the way around the tree and fill this basin which should be about three to four inches deep. Fill it twice with each irrigation.

Hard to say why the bark is splitting and falling off but I would pull the loose bark off and look for damage to the trunk such as holes for borers. The bark should be removed anyway of the trunk is dead under the bark and it is pulling away from the trunk. Often this type of situation turns into a long lingering death spiral for the tree over the next few years when it will decline more.