Desert Horticulture References

Q. I am relatively new to this desert environment and I know hardly anything about desert plants.  Would you recommend the best book(s) you have read that describe these desert plants? Which are best as decorative lawn plants? When to plant them and how to care for them?

A. I would focus on something written for the Las Vegas climate or secondly Tucson, Arizona and lastly the desert Southwest. Books I suggest are available on Amazon and Abe’s Books as well as other places if you search using the author names.

            Linn Mills from Las Vegas and Dick Post from Reno teamed up and wrote a book called the Nevada Gardeners Guide that has information split between both northern Nevada and southern Nevada. Its focus was to understand both Mojave Desert (Las Vegas) and Great Basin (Reno) conditions, soils and how to manage a landscape growing in them. 

            Tucson has a similar climate to Las Vegas; a bit warmer and humid in the winter and wetter during the summer months. From here is Plants for Dry Climates by Mary Rose Duffield and Warren Jones. It includes desert landscape design ideas as well. The newest edition includes and expanded section plant selection and care.

            Adjust books not written for the Las Vegas by recognizing that our winter low temperatures can get into the low twenties and even the upper teens on occasion. Trees you select for the “backbone” of your desert landscape should withstand these temperatures or you are asking for trouble. Play around with lesser important landscape plants that don’t tolerate these temperatures but don’t expect them to survive forever.

            A solid reference book is the Sunset Western Garden Book. It is not specific for the Las Vegas area but does a good job discussing desert soils, desert environments as well as an exhaustive list of plants suitable for advanced gardeners.

            I use Chris Martin’s Virtual Library of Phoenix Landscape Plants, free online and housed at Arizona State University, quite a bit. Just realize plants discussed are used in the Phoenix climate and soils. Adjust your selection for our colder winter temperatures and not as much heat in the summer.

            Several knowledgeable local experts like the Southern Nevada Water Authority (SNWA) searchable database of landscape plants for Las Vegas, called “Find Plants”.  It is a good online reference when first looking for possible plants to use.

Creeping Thyme Between Rocks and Pavers

Q. Some time ago you mentioned a plant used between stones or pavers, and when you step on it, it releases a fragrance. Can you tell me the name of that plant again? I would sure appreciate it.

A. I don’t remember a specific ornamental groundcover that I mentioned but creeping thyme will work, and it does come in culinary and nonculinary types. You can direct seed it in those cracks by preparing the soil with compost, watering the soil to settle it, lightly cover the seed with sand and keeping the soil moist until you see it germinating.

            You can use creeping thyme for cooking in a pinch but use new growth. Don’t plant it in extremely hot locations but it will work in an open area without reflected heat from a south or west facing wall. Plant it just like you would in a vegetable garden.

Can I Plant Texas Rangers Now?

Q. I recently purchased some Green Cloud Texas Rangers from a building supply store and was wondering if it is safe to plant them now since our weather is turning colder.

A, Since you emailed this question to me it froze in parts of the valley this past week. But not to worry. This kind of weather can be freakish this time of year. It normally does not freeze until the second week of December. But the ground is still warm. After you plant you want the roots to grow but you should not care about the top growing yet. The best planting time for woody plants is from late September until mid-November. You can still plant at other times but its just not as good because of root growth.

            The ground is still warm enough to plant. The magic number for landscape plant root growth is about 50F. Of course, roots of plants grow faster in warmer soils, but they will still grow at 50F. The ground never froze or was even close to freezing. The soil temperature rises up and down mimicking the air temperature, but these temperature swings are much smaller compared to air temperatures. For instance, in some areas vegetables like tomatoes, peppers and squash froze, but the ground never did. The soil in the ground was much warmer than the air.

            If you want the soil to warm up fast then keep it dark, fluffy, dry and in the sun. Those kinds of soils have wide temperature swings from very warm to very cold but still not as cold as the air. Landscape plant roots like to grow in those warm temperatures during the day. Soils that are not fluffy, wet and instead are covered by a surface mulch or in the shade stay cooler and don’t swing up and down as much.

            Surface mulch keeps soils warmer in the Fall and cooler in the Spring.

I Want Larger Bartlett Pear Fruit

Q. I have a ten-year-old Bartlett pear tree and the pears are kind of small, about 3 inches long. The label says they ripen in August but mine are not ripe until end of October. November. I pick them, leave them out in kitchen and they become juicy and ripe. I water the trees heavily once a week and the fruit improve. Is there any way to make tree produce larger fruit?

A. Bartlett pear has the potential here for getting the same size as in the stores with the same or better quality. It is a matter of how many fruit there are compared to the number of leaves. If there are a lot of fruit and not enough leaves to support the fruit, the fruit will be smaller. 

            For Bartlett pear you should have about 45 to 50 leaves for each piece of fruit so that they can get larger. The fruit is produced on spurs that form an average of five fruit per cluster. Remove all but one fruit per cluster when the fruit has recently set and is still very small. This may be hard to judge when the fruit is just starting out in the spring but try removing all but one of the fruit in each cluster. If you want the fruit larger, next year remove more. Do it when they are small. Don’t wait. The remaining fruit will get larger. This is called “thinning the crop” or just plain “thinning”.

            Fruit also needs water present to expand and get big when its growing. Make sure the tree gets adequate water while the fruit is enlarging. If the tree doesn’t, the fruit will not grow as much. I don’t know if your watering is often enough or not. But in midsummer I would guess the trees should be watered deeply two or three times a week. Once a week is good in the Fall when it cools off.

            Pick Bartlett pears when they are still green, but the green has changed from dark green to light green. Your label is wrong. Harvesting should be in about late September or early October, not August. If you aren’t sure, pick one and cut it open to look at the seeds. The seeds should be all brown then go ahead and pick them. Picking may last two weeks as they don’t all get ready to pick at once.

            Pick the fruit before they turn yellow because this keeps the fruit texture buttery instead of gritty. Then let them ripen in a cool place out of the sun until they are ready to eat in a few days. When you get them from the store they are sometimes green. Ripen them like that before eating them.

Irrigation Frequency of New Desert Ironwood Trees

Q. I have two desert ironwood trees that are ten years old, 12 to 16 feet tall, in my landscape. A nursery told me I should water these trees deep daily for 7 to 10 days. I did that and after the third day the leaves turned a pale yellow and fell off to the touch, so I have stopped watering. The soil moisture meter I use is showing 7 to 8. Any thoughts because I really don’t want to hurt these beautiful trees.

A. When you call these trees “desert ironwood” I am guessing you mean the ironwood native to the Sonoran Desert. It’s a beautiful native desert tree that does not need to be watered very often. It is considered an indicator tree for growing citrus so during cold weather in southern Nevada it might get damaged. There are other trees called ironwood as well.

            Because it grows in the desert, it is not used to getting water very often. When you water this tree, irrigate the area under its canopy to a depth in the soil about 18 to 24 inches. Then don’t water again until the soil dries out. Because it’s a desert tree, it will not like wet soil but soil that occasionally gets wet. That’s why the leaves are yellowing and falling off; watering is too often and the roots are suffocating.

            On the soil moisture sensor, or meter that you have, the needle should be in the three or four spot before you water again. The meter reads zero to ten with ten being sopping wet. You want the soil to be on the dry side about six inches deep, not the wet side when you water it again.

            When you do water, try a hose, an inexpensive sprinkler that screws onto the end of the hose and a mechanical timer that shuts off the water. If you are like me, I forget to turn it off. The mechanical timer will shut it off for me. Set it for one hour. Take a length of rebar and stick it into the ground in three places and make sure the water got to the right depth. If the water isn’t deep enough then water for 15 minutes more.

I Want Plants That Bloom All Season Long

Q.  I am looking for plants that bloom all season long like lantana. Can you help me?

A. I would rather that you use a searchable plant database online like the one created by Southern Nevada Water Authority. It’s a good one. Google or use your favorite internet browser and type in “find plants SNWA”. The Sunset Zone for Las Vegas is Zone 11. The rest of the information needed for the database should be straight forward. Use this before you go to the nursery and get a list of plants that you want.

            If you want plants selection advice from me, ask for five suggestions at your nursery and then I can help you pick which might be best. There is a lot of information available to help you decide. Select trees and shrubs that you cannot afford to lose using a minimum winter temperature of 20F. If we have a few warm winters in a row then you won’t lose anything!

            If you select plants that tolerate winter temperatures above this temperature then expect to lose them occasionally during cold winters. Even at 20F we will have 30 to 50-year freezes that will get as low as 12F. If the 20F plants are established in the landscape well before that, they will probably survive.

Should I Add Worms to My Raised Beds?

Q. I made a couple of raised bed planters for tomatoes and peppers and currently have garlic, spinach and lettuce growing. Would adding worms to the soil help?

A. Worm benefits far outweigh any feeding damage they do to plant roots. I know I will get some heat for saying this, but earthworms can create some damage to small plant roots. Just like ants can carry away seeds that you plant. Too much of a good thing can be too much.

            If you do add some earthworms to your garden plot, you don’t need to add many. They multiply quickly when organics and moisture are present. The addition of compost to raw desert soil and growing plants in it is usually enough. I will see earthworms in soils that I amend and cover with woodchips in abundance the first year after planting. Adding worms to your soil will speed up what will occur naturally. 

Spider Mites on Italian Cypress Is a Hot Weather Problem

Q. My Italian cypress had spider mites, so I sprayed the trees with an insecticide about six weeks ago. Nearby Italian cypress trees are also full of spider mites. I was going to spray them with an insecticide until I listened to your Desert Horticulture podcast which told me to use a miticide instead. Which one should I use?

This Browning could be from spider mites, watering too often, or borers. If it occurs in the middle of summer it's very likely spider mites.

A. Spider mites are a hot weather insect so spraying when it's not summer just for them doesn’t make much sense. However, spraying oils in Fall and Winter months makes perfect sense for insects that might spend the winter on your trees.

Horticultural oils, sometimes called dormant oil or spray oil, is the best insurance to prevent insect outbreaks like aphids, spider mites, and scale insects.

            Remember, spraying insecticides make mite problems more likely on susceptible plants like Italian cypress. Miticides, unlike insecticides, are less likely to cause mite problems later. Spider mites are nearly always present on all plants they feed on. There are lots of insects that feed on spider mites as well and keep them in check.

Spider mites, like their name suggests, usually leave a webbing that you can see when there is damage.

            These predatory insects hunt down spider mites and use them for food. Think coyotes and rabbits. Spraying traditional insecticides like Malathion, Sevin and even organic insecticides like Neem oil or soap and water kills most insects off, good ones as well as the bad one you wanted to control. The primary benefit of organic sprays are its environmental safety and short life after its sprayed.

When spider mites are active they can create a bluish green cast when they are actively feeding and often times then leaves of Italian Cypress are "dusty". Spider mite damage always starts in the heat of the summer.

            If an insecticide must be sprayed for some reason, watch the sprayed plants very carefully during hot weather to see if spider mites become a problem or not. Frequently spider mites will become a problem after spraying an insecticide because their predators were killed. I realize sometimes you must, but spray insecticides as a last resort.

Close-up of the needles or foliage of Italian Cypress and spider mite damage.

            Miticides are chosen because spider mites are more like spiders than insects and sprays that kill insects oftentimes don’t kill spider mites. I am glad you did not use an insecticide for mite control. It would have made the problem worse and probably not killed the spider mites.

            Use the University of California Integrated Pest Management websites (“Google” them by using your favorite search engine and typing in “UCIPM” and “spider mites”). Read these notes. They are written by entomologists who specialize in controlling pests. After reading these notes you will be better informed than 90% of the landscapers spraying plants.

            The UCIPM notes will recommend spraying oils like canola, clove and cinnamon oils as well as horticultural oils and sulfur sprays to control spider mites. In our hot desert environment these sprays may damage plants during the hot months. It is cool enough in the Fall, Winter and Spring you can spray oils without damaging most plants. Plants that may be damaged will be listed on the label.

Didn't Think Italian Cypress Got Borers. I Was Wrong!

Q. I had a lot of borer damage to my trees so last summer I cut out most of the large branches and reduced the height of the trees to about 10 feet and let them grow back. Then I treated the soil with an insecticide, surfactant and fertilizer. That was my counterattack regarding the borers.

Borer exit holes in the trunk of Italian Cypress sent in by an alert reader.

A. Make sure trees that you do cut back will grow back. Some trees like most ash trees will not grow back very well if they are pruned severely. Also make sure the pruning instruments are all sanitized before pruning.

This formulation of imidacloprid (this name is found under ingredients) is probably the most common one found on shelves. Shop around because there may be some that are less expensive. Compare the percentage of imidacloprid on the label with the price of products. Higher percentages single just means you get more "bang for the buck".

            Insecticides like Imidacloprid (active ingredient) used as a soil drench (mixed with water and contained on the surface of the soil above the roots) are systemic and taken up by roots of the tree and kill many types of borers. Whatever insecticide you use should be systemic and have a label that says it is effective against wood boring insects.

Excerpt from the product label of Imidacloprid 2F manufactured by Prime Source LLC. The active ingredient is available from several manufacturers so it is imperative to read the product label before making any applications.

            If the insecticide has “staying power” inside the tree then I would apply it after the tree flowers. This is usually in early spring. Long-lasting, systemic insecticides like Imidacloprid are suspected to harm honeybees. There is a possibility the insecticide could be available to honeybees if it is applied just before flowering.

A portion of the product label for Imidacloprid 2F warning about killing honeybees. Be careful when you spray insecticides or apply them as a drench to the soil.

            I am not sure why you are using a surfactant unless it is to help this insecticide drench move into the soil faster after drenching the area. Surfactants are a very broad category of  spray additives but usually used to move liquid fertilizers, insecticides and fungicides inside plant leaves when they are sprayed.

One example of a surfactant. When mixed with a spray it helps the product get inside leaves or stems. When mixed with a liquid drench it might help the drench move into the soil better. 

Pruning Heresy for Italian Cypress

Q. My Italian cypress are getting too tall. Can I top them to keep them smaller?

Here a homeowner "topped" their Italian Cypress to control its height. It works but it will increase the width of the tree through new growth to the sides rather than directly upward.

A. Topping trees is not a good idea but in this case it will work because underneath all that foliage is a central trunk. It’s not the best way to handle this dilemma but if it is done when the tree is smaller it will help prevent it from getting too tall. Removing several feet of the top this way is questionable.

            Remove the pointed top just below the height wanted. This keeps the tree’s height in check, but it will grow wider than if it were left alone. Hindsight is 20/20. It would have been better to realize these are 40 to 60-foot trees before buying or planting them.

Sometimes the top will die in Italian cypress from borers or spider mites. The top is dead. Removal of this debt growth and the removal of living growth on other trees at the same height will limit its maximum height but not its width.

            The bad pruning method is shearing the tree with a hedge shears. Shearing does prevent long “floppy branches” from developing but it causes other problems. Shearing increases the density of the tree in the outer few inches while the inside branches become naked. The inside of the tree gets darker and darker as shearing increases, and this prevents any greenery from forming.

Italian Cypress has such a dense canopy that anyone using a hedge shears to prune them has to be very careful not to cut into the brown area just an inch or so to the inside. This growth is very slow to grow back or doesn't grow back at all.

            Eventually any deep cuts past these three or four inches outside edge will expose the naked larger branches inside which have no greenery. None will develop from old wood on Italian cypress, so it won’t grow back. Worse than a bad haircut!

Be Careful Watering Italian Cypress

Q. I am purchasing some Italian cypress as a visual barrier between my neighbors and myself. I understand they are evergreen. Any thoughts?

Italian Cypress can be 40 to 60 feet tall and 4 to 8 feet wide so make sure you have the room for them. General rule of thumb is to use small trees for single-story homes and medium-size trees for two-story homes. It's an added expense if you have to keep pruning them to keep them at the right size.

A. Italian cypress is a big tree so make sure you have room for it, and it is in scale with your home and landscape. It can be 40 to 60 feet tall and 4 to 8 feet wide. It is a good visual barrier but tall!

            Italian cypress is a Mediterranean plant, not a desert plant. This tree came from climates with cool wet winters and hot dry summers so don't water too often but more often than true natives! Put it on a valve that waters palms, fruit trees, other landscape trees and shrubs but not with lawns, flower beds or vegetable beds. It will not like it if it is watered with the same frequency as cacti and native desert trees like Palo Verde and mesquite unless they are watered too often!

One sign they are watered too often is when the growth gets so much that it starts to droop. An occasional drooping branch can be pruned back to the inside of the canopy and removed. It's a problem if you have lots of these drooping branches and it is a poor alternative if you must wrap them with green tape. Learn how to water them properly.

            Italian cypress with long drooping branches is a sign it is getting too much water. Either it is watered too often, or the soil is not draining water fast enough. Hedge shearing (not recommended) keeps them in check but using a hand pruner instead is a better option.

Shearing them with a hedge shears is one method to make them look pretty and keep them in bounds. But that is expensive to do twice a year.

            Enough water should be applied each time to wet the soil to at least two feet deep. The amount to apply varies because of the soil so you will have to play around with the number and size of the emitters. But when you apply water, it should wet the area under the canopy out to the ends of the branches. Normally I will tell people AT LEAST half the area but these trees are narrow and upright so water the entire area.

How Far Apart When Planting a Hedge?

Q. How far apart should I plant my hedge shrubs to make a hedge?

A. It depends on the plant but a general rule of thumb for shrubs that grow just as wide as they are tall is to plant them the same distance as their mature height. If you plant them this far apart they will grow up touching each other. If you want them to fill in faster, then plant them a bit closer.

Pruning shrubs with a hedge shears tells me you don't know how to prune.

            Planting them too close together causes them to grow together but they will shade each other. That’s not a problem for the hedge but you will spend more money than you need to in plants.

These shrubs were planted too close together. You can tell because its all a bunch of wood stems at the base. A way to correct this problem now is to remove every other shrub and cut them back to their distance apart and cut the biggest branches to about 8 inches off of the ground. The hedge should fill in again in 2 to 3 years depending on how fast they grow. 

Transplanting Sago Palm - Do it Right

Q. Do you have any advice on digging and transplanting a Sago palm this time of year? It’s the roots I’m considering. I failed last time maybe because it was too hot.

Nicely cared for cycad or Sago Palm

A. The ideal time to move sago palm, or cycad, is in the early Fall or early Spring but you can do it now even though its cold. It’s just not optimum. Evaluate your situation. If it has been in the ground more than three years, it is more difficult to move without damaging it. It helps if it was drip irrigated with no other irrigation within 10 feet or so. This isolates the roots and keeps what you need to move closer to the plant.

These plants like a little bit of shade or protection from late afternoon sun. They just do better.

            Two things are important when you move a plant: take as much of the roots and soil as possible during the move and reduce the top by 1/3 to compensate for root losses during the relocation. You will have more success if it is moved into a spot with light shade, not full sun.

            Here’s the process. I will put more information on my blog for you.

Cycad transplanting process

•             Remove fronds from the bottom toward the top so the remaining fronds are no more than a 45-degree angle from horizontal. The central fronds should be protected. The older palm fronds can be removed. Sago palm grows from the center straight up and the fronds become lower with age. Mark which side of the plant faces north. You will orient this side to the north again when planting.
•             Prepare the soil and hole in the new location so you can place it into its new home and plant it as quickly as possible. The hole should be about the same depth as the rootball you are moving. The hole with amended soil will be much bigger.
•             Move everything away from the sago palm so that it is surrounded by bare soil and then water the soil until it is sopping wet. Using a sharp, clean shovel, slice the roots of the palm at about 12 inches from the trunk. Otherwise, leave it undisturbed. The next day after water has drained, leverage the plant upward carefully from its old location while cutting any remaining roots that might hold it back.
•             Placing the rootball and plant on an old piece of carpet or strong fabric by lifting the rootball, carefully move the plant to its new location without breaking the soil around the rootball. Very important.
•             Orient the sago palm with the north side facing north and backfill around the rootball using amended soil as a soil slurry to remove air pockets. It will not need to be staked. Add any amendments to the soil you feel is necessary to improve rooting. I personally don’t use anything more than the amended soil.
•             After the soil has settled and starts to dry, cover the area surrounding the sago palm with woodchips. Woodchips are a better soil covering (mulch) than rock for sago palm.

Plant During Winter but Not As Good As Fall Planting

Q. I would like to plant a pomegranate tree this Fall but I am worried that the weather is going to be cooling down soon. Do you think I missed my opportunity for planting, and should I wait for Spring?

A. Just because it is getting colder doesn’t mean you can’t plant. Ideally you want a few weeks of root growth in the Fall after planting. The timing may not be optimum for root growth when soil temperatures are cold, but it will still work out. If you find a variety you like, get it in the ground.

            Temperate plant roots (like pomegranate) grow best when soil temperatures are between 60 to 75F but they still grow even when soil temperatures are as low as 45F. They just don’t grow as fast. Try to plant early enough so that there are 4 to 5 weeks of warm soil temperatures before the soil gets cold.

Estimating soil temperature

            How to estimate the soil temperature? The best way is to buy a soil thermometer for about $15 and measure for yourself but otherwise you can make a rough approximation.  

Soil thermometer on Amazon

Soils are always a bit warmer than air temperatures. Take the average air temperature over the past couple of weeks (low + high and divide by two) and add 5 degrees. Surface mulch, rock or woodchips, conserve soil warmth in the Fall and insulate soil from heat in the Spring and Summer months.

            In my experience, using your sense of touch is accurate to within about 5 degrees F of temperatures ranging from the refrigerator (40F) to the spa (105F).

            Fall planting is always superior to Spring planting of winter hardy plants.

Steer Manure Is Stinky but Can Be Used

Q. We applied Red Star steer manure as a topsoil during overseeding tall fescue three days ago. Is it ok to apply granulated fertilizer to this or should we wait longer?

Stinky Steer manure can be used for top dressing seed in a lawn or even vegetable garden but let it age

A. So we are on the same page on this, you are spreading some seed on your tall fescue lawn to increase its density, thickening up some thin areas and maybe improving the look of your lawn because of some brown spots or dead areas. Once the seed is spread and fertilizer is applied, you are spreading a thin layer of steer manure as a “topdressing” (you are calling it “topsoil”) to improve the germination of the seed. The best time to do all this is from about mid-September to mid-October. It is getting late now.

Manure used for topdressing

            Bagged steer manure was used in the past as a topdressing for lawns when overseeding. It was smelly but it worked well. Years ago, you knew it was fall overseeding time because of the steer manure smell in the neighborhood. Now there are commercial topdressing products available but bagged steer manure still works.

Rules for overseeding

            In lawn seed germination, a rule to follow for good seed germination when overseeding lawns is good “soil and seed contact”. It is important that the seed applied is in contact with the soil after the application is done. The steer manure or topdressing was a “blanket” that pushed the seed down and helped keep the area moist.

            Make sure the lawn is mowed as short as possible (for fescue I wouldn’t mow shorter than one inch) and any debris on the soil surface (thatch) is disturbed or removed. This is done with a dethatcher, power rake or verticutter. This can be done by hand using a garden rake or gasoline driven if it’s a large area. For best results you should see bare soil when you are finished.

            After the lawn has been “dethatched” is the best time to apply a starter fertilizer for overseeding because it is high in phosphorus. This fertilizer is applied at this time, so it lands on bare soil along with the seed used for overseeding. The phosphorus is the part of the fertilizer you want on the bare soil because it doesn’t help the seed as much if it is applied after the job is finished. 

Phosphorus fertilizer should be mixed into the soil

Remember this in the future. It’s the same fertilizer used in vegetable gardens during soil preparation prior to seeding or planting vegetable transplants. The final application is a thin layer of topdressing, in your case the steer manure.

            Applying a starter fertilizer after it’s all finished is not the best but better than nothing. Go ahead and apply it. It’s not optimum but it will do some good as the seed is germinating and taking root.

Watering Lantana and Roses in the Mojave Desert

Q. I need suggestions for watering times and days to water in the summer for sprinklers watering trees in lawns, lantana bushes and rose bushes with drip irrigation.

It isn't just the watering that's important for roses but soil health is well. Lantana is much more tolerant of rock and poor soils than roses.

A. When watering trees in a lawn, give the trees extra watering separately from the lawn since the trees should be watered more deeply than the grass. In the summer do this about every two weeks in sandy soil, less often in heavier soils. 

1. Grass is watered 8 to 12 inches deep 
2. while small trees (less than 20 feet tall) are watered 18 inches, deep and 
3. medium height trees (less than 40 feet tall) are watered 24 inches deep. This can be done with a sprinkler on the end of a hose and a mechanical timer. This improves tree growth and establishment if the lawn is being watered carefully.

            Watering times for other plants are also suggested by your water provider. Lantana is a shallow rooted small woody shrub. It should be watered about 12 inches deep and no more than every other day in the summer. Water all its roots on one day and then hold off at least one day before watering again. Lantana will tolerate rock covering the soil surrounding it. Just make sure you apply fertilizer about three times each year. When the top turns brown, cut it back to 1 to 2 inches above the soil.

             Roses are different. Watering frequency is the same as lantana, but they don’t like the soil covered in rock. They like woodchips that disintegrate, covering the soil surface, and surrounded by soil that is rich. Plant them in amended soil and keep the soil covered with woodchips.

Cutting Off Roots from Trees is a Judgement Call

Q. When our landscapers installed new water lines for irrigation they cut through two major roots on a Chitalpa tree; one root was 4 inches in diameter and the other 1 ½ inches in diameter. These water lines could have been installed under the roots instead of cutting them. I am not sure why they did it this way. I am concerned about the future health of the tree.

A bit hard to see but a large Chitalpa root cut by landscaper.

A. If this is a problem for the tree, is a difficult question to answer. Will cutting the roots of a tree cause it to die? Cutting tree roots always damages the tree. Can the tree recover from this damage? The right answer is, it depends. From your description, the root removal done sounds ominous.

Tree roots grow where water is applied. If water is applied in shallow irrigations, it leads to shallow roots.

            You can typically remove about one third of the total roots with no problem. This is done sometimes when trenches are cut in the soil for burying irrigation lines. When roots are cut. But when roots are cut, about 1/3 of the top should be removed as well. This removal of part of the top puts the top and roots back in balance with each other. How much of the total roots were removed in your tree’s case? That is difficult to estimate.

Strangling roots should be removed as young as possible for obvious reasons.

            Look at the distribution of water applied for irrigation. This helps determine where the roots might be. Roots grow toward water because the soil is wetter in these locations. If there is a lawn close to the tree, then roots grow vigorously toward the lawn and less vigorously toward its own drip emitters. If other plants are growing near the Chitalpa, tree roots will likely grow toward the majority of drip emitters because there is more water there.

Trees growing in lawns oftentimes grow shallow roots because lawns are watered with shallow irrigations. These roots can be removed if they are far enough from the trunk and are not a major root of the tree used for water uptake, soil nutrients important to the tree or used for major support.

            At the very least, remove about 1/3 of the top. Remove entire limbs rather than giving it a “butch haircut” and removing the ends of lots of branches. Removing two or three major limbs is probably enough in your trees case.

This native mesquite near a river in Jerez, Mexico, sent its roots deep after underground water coming from the river.

            As a precaution, I would stake this tree. Major roots of trees are used for tree stability particularly during strong winds. The tree might need to be staked until the roots secure the tree in the ground. I would do it in case it is needed. Don’t wait until the tree starts to lean because of strong winds. Remove the stakes when the tree is stable. This might be one season of growth for smaller trees or up to three years for larger trees.

Be Careful Where You Plant Carolina Cherry Laurel

Q. My gardener said my Carolina cherry laurel died from a pest. He is cutting it out and suggested treating the soil and waiting until March to plant anything new. He is suggesting a Holly Oak which sources day can reach 30 to 60 feet in height! That’s quite a range.

Typical leaf scorch of Carolina Cherry Laurel planted in desert soils in hot locations

A. Most likely the Carolina cherry laurel died due to where and how it was planted and maintained. It is native to the Carolinas (hence its name) and should tell you about its suitability for desert climates and where it might survive in local landscapes.

Carolina cherry laurel probably should never be surrounded by rock mulch

            Holly oak is big, but it grows slowly. It will grow about a foot a year with irrigation and handle lawns well. It is not used much anymore but a good tree for large landscapes, not smaller residential landscapes. Pick something smaller. Single story homes should have trees with a 20 to 25-foot mature height. Two story homes can handle 30 to 40-foot-tall trees. No bigger. This is just too big for most homes.

Expect Different Kinds of Mushrooms After Rain

Q. These creepy white “things” keep cropping-up out of the ground all over my backyard. What are they and are they dangerous? I am thinking they might be a mushroom or fugus of some sort. I am concerned because in the past, I had a serious, invasive fungal infection (aspergillus) requiring surgery.

Many different types of mushrooms can appear after a rain and there is wood in the soil or on the surface

A. Yes, these are mushrooms (fungal) and they “feed” from decaying wood, woodchips, particles of wood or rotting woody roots in the soil. They are common in the spring and fall months after rains when there is wood in the ground getting wet and rotting. The wood might be from woodchips used as a surface mulch or signal dead and decaying roots of trees. You might see some in compost piles as well. Oyster mushrooms, edible types of mushrooms, are commonly grown in decaying wood chips so it can be a perfect habitat for some types of mushrooms. But its natural for them.

Sometimes mushrooms grow in woodchips and they look like mushrooms with the stalk that supports the cap

            Several types of mushrooms appear in the cooler spring and fall months after a rain. Most are not poisonous but that doesn’t mean they can be eaten. The mushrooms seen can range from puffballs to traditional mushrooms to slime molds which look like vomit on the ground. I have been told by some they can make pets sick if eaten and may require a visit to the vet but its normally not life threatening.

Sometimes these mushrooms grow beneath the soil and make fleshy underground balls

            They are more of a nuisance to most people. To get rid of them and keep them from spreading, vigorously rake the area when they are young and first seen to prevent them from maturing. These mushrooms open up when mature and spread “spores” which are their “seeds” for spreading to other wood mulch during rains.

Sometimes they grow in piles of woodchips or compost

             I realize there are people very sensitive to the spores of some types of fungi including mushrooms. Take some pictures of the problem. It is best to check with a physician to be sure.

Sometimes they cause an allergic reaction or a rash

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Best Books and Websites for Plant Selection in Las Vegas

Q. I am relatively new to this desert environment and I know hardly anything about desert plants.  Would you recommend the best book(s) you have read that describe these desert plants? Which are best as decorative lawn plants? When to plant them and how to care for them?

A. I would focus on something written for the Las Vegas climate or secondly Tucson, Arizona and lastly the desert Southwest.

            Tucson has a very similar climate to Las Vegas; a bit warmer in the winter and a bit more humid and wetter during the summer months. Tucson is in the Sonoran Desert which gets 250% more water (about ten inches of rain each year) than our Mojave Desert (four inches of rain each year) and generally has better soils.

            Adjust books not specifically for the Las Vegas area to our climate and soils by recognizing that our winter low temperatures can and frequently get into the low twenties and even the upper teens on occasion. Trees you select for the “backbone” of your desert landscape should withstand these temperatures or you are asking for trouble. Play around with lesser landscape plants that don’t tolerate these temperatures but don’t expect them to survive forever.

            Linn Mills from Las Vegas and Dick Post from Reno teamed up and wrote a book called the Nevada Gardeners Guide that has information split between both northern Nevada and southern Nevada. Its focus was to understand both Mojave Desert (Las Vegas) and Great Basin (Reno) conditions, soils and how to manage a landscape growing in them. Their book is available on Amazon and Abes Books if you search using the author names. It would be a good book for Pahrump, St. George and Kingman, Arizona besides Las Vegas and Reno area.

            Another book I used in the past is Plants for Dry Climates written out of the Tucson area by Mary Rose Duffield and Warren Jones. As well as plants, it includes desert landscape design ideas. It is also available on Amazon and Abes Books. The newest edition includes and expanded section plant selection and care. The original version presents a concept on desert landscaping called the minioasis landscape design concept which I really like as well as landscape plants that are successful here. It applies to any of our desert climates including the Chihuahuan, Sonoran and Mojave Deserts of the Southwest but less to the Great Basin area.

            A solid reference book you should have in your library is the Sunset Western Garden Book. It is not specific for the Las Vegas area but does a good job discussing desert soils, desert environments as well as an exhaustive list of plants and their descriptions suitable for many different kinds of Western environments.

            As far as free websites on plants online, I reference Chris Martin’s Virtual Library of Phoenix Landscape Plants housed at Arizona State University quite a bit. Just realize its focus is Phoenix climate and soils, is 5 to 10 degrees warmer in the winter and not quite as hot in the summer. It is perfect for Laughlin, Bullhead City and Lake Havasu, Arizona as is. It is excellent for Las Vegas selections but just keep in mind the temperature limitations between Phoenix and Las Vegas. This website doesn’t pull any punches on landscape plant shortcomings and how well they perform in desert climates and soils. Once you have made a plant selection, it is a good bench check on how it will perform here.

            Several knowledgeable local experts like the Southern Nevada Water Authority (SNWA) searchable database of landscape plants for Las Vegas, called “Find Plants”. It is accurate with information presented on plants but I find it somewhat cumberson to use at times. It is a good site when you are first looking for possible plants to use.