This is one of the most common questions I’m asked. Why is my plant yellow? In Desert Horticulture, the reasons can be many. I’ll try to list here as many as I can think of and how to tell them apart. Lack of Iron Plants must have iron. If they don’t, their newest leaves turn yellow. It’s not totally correct to say it’s a lack of iron. There is plenty of iron in the soil, it’s just not available to the plant. The plant can’t use it because of some chemistry problems involving the soil. The pH is too high or its alkaline. This type of soil chemistry turns the iron in the soil into something that the plant can’t use. Iron chlorosis when it’s mild is on the new leaves and the veins of the leaves stay darker green than the blade. If this is early in the season, the future leaves may turn bright yellow with no green veins. Here it is on Apple. Because of iron is going to be a big problem that season, the yellowing starts out early in the season and on progressively gets worse and worse. The first thing you see are leaves with a light green color with darker veins. As the season progresses the green veins may disappear and the leaf is just plain yellow. As it gets hot, many plants can’t handle the heat anymore because they are not as healthy and the edges begin to scorch, turn brown. Yellowing due to a lack of available iron, also called iron chlorosis, can cause severe yellowing in leaves and weaken them so much that they are much more susceptible to heat than they would be if they were healthy. Manganese deficiency will cause the leaves do look very similar to this but it’s not as common as iron. Spraying the leaf with a little bit of iron solution and soapy water will tell you if it’s iron or not. Some plants have leaves that react differently when iron is a problem. But the yellowing is always on the newest growth. Iron chlorosis looks different on bottlebrush but the yellow leaves are the newest leaves at the tips of the branches. Control yellow leaves due to iron. If you know you have a plant that has this tendency every year, apply an iron chelate spread beneath it with lots of water to get it out of the sunlight and into the soil before new growth begins in the spring.Several chelates are available but I usually push people toward the chelate abbreviated as EDDHA. This is because this chelate works in all types of soil whereas other chelates may or may not. This is an iron fertilizer containing the chelate EDDHA. Because of the soil chemistry, other chelates may or may not work in your soil. Using the iron chelate EDDHA works in all types of soils and it’s a safe bet when looking for a soil treatment in the spring for correcting yellow leaves due to iron problems. The second method of applying iron is to the leaves as a liquid spray. This is done later in the season when the leaves are out and applying an iron chelate to the soil may no longer work effectively. Watch my video on applying iron to the soil or apply an iron spray to the leaves. I don’t have a video on doing the ion spray yet but hope to do it soon and post it on my channel.  When making the iron spray concoction I would use distilled water, the iron fertilizer mixed in the water with about a tablespoon of liquid detergent mixed with it afterwards. Spray the leaves until this mixture begins dripping from the leaves.This spray concoction may need to be applied three or four times a few days apart to get it dark green. Another option you have is to do the soil application and the foliar spray at the same time. We have done that in the Ahern Orchard and had good luck with it in late spring or May. Salts Salts in the soil can also cause leaves to yellow but this is often times accompanied by damage to the edges of the leaves. The veins can appear green just like it was described above but the edges of the leaves are the telltale sign that salt in the soil may be the problem. This is yellowing of the leaves of a pepper plant because the of salts in the compost mixed in the soil and the heat of the day. Edges of the leaves scorching was the telltale sign it was salt damage. Fixing salt damage. There isn’t anything that you can do to the existing leaves that show the yellowing and browning on the edges when salt is causing the damage. But the new growth will show improvement just threw better irrigation management. Flush the soil with lots of water to remove the high level of salts. The soil must drain the water for this to work. If the soil doesn’t drain, then drainage is the problem combined with the salts. To fix that, you have to make the soil drain. A different topic. Intense Sunlight and Yellowing Some plants don’t belong in strong sunlight.Know which plants can handle intense desert sunlight and which ones can’t. Just because a blog or a YouTube video says you can plant it in full sun doesn’t mean you can plant it in full sun in the desert. It depends on the plant. This is why Desert Horticulture can be so different from “normal” horticulture. This cycad or Sago Palm has yellow leaves because it’s in full sun near a hot wall and surrounded by hot rock mulch. This plant will perform much better in a cooler location, woodchip mulch with some filtered light. Carolina cherry laurel is another plant that can show yellowing, similar to the cycad, if it’s planted in intense sunlight and surrounded by rock mulch. Know

Join me on this episode of Desert Horticulture. We will discuss the Leaffooted Plant Bug (does it deserve to be capitalized?), controlling some weeds like sandbur and puncturevine, planting horsetail, twisted myrtle problems, and ants climbing inside figs. This and more in this episode of Desert Horticulture.

Q. I’ve been using adjustable  drip emitters and replacing them every year because they plug from the hard water. They sputter air or just don’t emit water when they start a watering cycle.  When I find one like that, I open up the watering rate until a steady flow is achieved, but it doesn’t seem to last. A. Sounds like several possible problems going on with your drip system. Let’s start with the easy ones first. Make sure your drip irrigation system has a filter installed to prevent drip emitters from plugging and a pressure regulator to prevent high water pressure from damaging the emitters. A pressure regulator (black and white on the left) and a screen filter canister (right) together inside an irrigation box. Arrows on them indicate the direction water should flow when installing them.              A removable flush cap must be on each of the irrigation lines so that the system can be “flushed” on a regular basis. This helps to prevent emitters from plugging. I will talk more about this in a minute. Some flush caps unscrew to release water.              The most popular filter for residential use is the inexpensive screen filter. It is oftentimes a black canister installed close to the irrigation valve used for drip irrigation. It is normally installed immediately downstream of the valve in the same irrigation box.             The screen inside the filter should be removed regularly and gently cleaned or replaced if damaged. Clean the filter two or three times a year when using city water, more often if you’re using well water. The dirtier the water, the more often the filter needs to be cleaned. Pressure regulators come in different static pressures and there are adjustable ones if you aren’t sure of the pressure needed or it varies.             Pressure regulators prevent the water pressure from rising above the limits allowed for the drip emitter to operate normally. They don’t increase water pressure if it is too low. Match the pressure regulator to the pressure range recommended for correct operation of the emitters. It’s more complicated with a large drip irrigation system. In cases like these, use adjustable pressure regulators. Flushing can involve the use of valves, screw caps or be as simple as this figure 8.             Flush caps or valves must terminate all drip irrigation lines that carry water. It is important to “flush” these lines by opening the irrigation line when the system is operating and let the water run until it comes out clean. Open each flush cap sequentially for each drip irrigation line the same time the filter is cleaned. Flush the line if repairs are done on the system that allows dirt to enter that might plug emitters. The number one reason for failure of a drip system is not flushing drip irrigation lines and cleaning the filters regularly and after repairs. Air release valve manufactured by Jain Irrigation. It is inserted directly into polyethylene drip tubing to exhaust air in the drip lines. Water forces it shut.              Air release valves like this one from Netafim are also made to be screwed into PVC irrigation pipe as well. Air release valves are an add-on to the drip system if trapped air is a problem or takes a long time for the drip emitters to start dripping water. Air release valves are inexpensive and exhaust trapped air in the system quickly before the irrigation lines become fully pressurized with water. They are usually installed at the end of a drip irrigation line or in combination with a flush cap or flush valve. Adjustable drip emitters are convenient because you can open or close the emitter to deliver more or less water. But they are not precise and are not pressure compensated.             Adjustable drip emitters are not “pressure compensated”. This means they deliver water at variable amounts depending on the water pressure and their elevation relative to other emitters. One reason I don’t like adjustable emitters is because of their lack of precision; when one adjustable emitter is opened to allow a greater flow of water, less water flows from the other emitters on the same line.

Flowers emerging from the spathe on a Canary Island date palm. Q. We have several Mexican fan palms, plus a few identified as hybrid California and Mexican fan palms, in our backyard. They are sending out flower stalks and make a huge mess for anybody who has a pool. One of my neighbors said that only female palm trees produce these messy stalks. True? Dates (fruit) produced by a female date palm. A. There are hundreds of different kinds of palm trees and palms are variable whether they are male, female or produce both types of flowers on the same tree! For instance, both the Mexican and California fan palms have male and female flowers on the same tree. But the date palms, both the true date and the Canary Island date palm, are either all male trees or all female trees but they never have male and female flowers on the same tree. Suckers from date palm. They can be removed and planted when they are older and their chances of survival are better. The suckers will be the same sex as the parent tree.             So, if you have the California or Mexican fan palms then all of them are “messy”.  But date palms are different. Male date palms are less messy around pools than female date palms. Look for fruit on older female date palms if you aren’t sure whether they are male or female (they must be about six feet tall before females start producing fruit).             It is nearly impossible to “sex” a tree before it starts producing flowers or fruit if grown from seed. Palms propagated from suckers will be the same sex as the parent tree. California and Mexican fan palms are started from seed. Date palms may be started from seed or suckers.

Q. I tried to start fig trees by cuttings taken from my big, sturdy tree and putting them in water or soil. Not much luck. How can I start new fig trees? A. Figs are easy to start from cuttings provided you take them at the right time of year, the cuttings are the correct age and they are placed in a soil or medium that drains water and free from disease. They can also be started by air layering or rooting suckers at the base of the tree trunk. Placing cuttings in jars of water or using garden soil can lead to drainage and disease problems. Suckers growing from the base of the trunk can be covered with soil, kept moist and they will grow roots. These rooted suckers can be potted and put in indirect light until fully rooted and then planted. Air layering or marcottage can be used to form roots coming from damage done to stems on many different types of trees. Just do it at the right time.             Cuttings taken from new growth in the spring are 6 to 8 inches long and range in diameter from pencil sized to as big as your thumb. With a sharp, sanitized pruning shears remove a length of new growth. Cut this new growth into pieces just below a node on the bottom and just above a node on the top. Include at least four nodes on each cutting and remove any leaves present on the cutting. Cuttings don’t have to be from large stems.             Push these cuttings into perlite or sanitized potting soil in a clean container that drains. Stick these cuttings upright, a couple of inches apart, so that two of the nodes are beneath the soil or media and two are above. Use a rooting powder for a larger number of roots that are more vigorous. Wine grape cuttings stuck in an amended soil and rooted.             Place this container out of the direct sun but where there is plenty of indirect sunlight and keep it moist. Rooting occurs first followed by leaf development. Leaf development is a sign rooting has occurred. Grape cutting forming roots at its nodes.             Figs can also be started from the suckers at the base of the tree or by air layering. The base of the tree is mounded with soil around the suckers and kept moist. Damaging the sucker before mounding encourages root development. Traditional air layering methods can be used but keep them in the shade of the canopy so it is not damaged by direct sunlight.

Q. You said the main crop of figs is the second crop of figs. But on my Black Mission fig, the first crop has large fruit, and the second crop, although much more plentiful, has fruit that is about 1/3 the size. Both are delicious. Fruit size has more to do with the distribution of “food” for fruit growth and the number of fruit it is divided into. A. The size of the fruit has more to do with the total number of fruit growing on the tree; the fewer fruit on the tree, the larger each individual fruit becomes. The term “main crop” has more to do with where on the tree the fruit originates. Picture showing both Briba and Main crop figs coming on at the same time but at two different locations on the same stem.             Fruit from figs comes first from stems that grew last year as well as a second crop on this year’s stems. “Main crop” figs are only produced on stems that grew this year. The early or first figs, called the “Briba crop”, come from stems that grew the previous year.             Some people claim that “Main crop” figs taste better than the Briba crop figs. I have never tasted any difference between the two. But generally smaller figs have more flavor than the larger figs and there is a difference in taste between different varieties of figs. 

This is my foot on top of some raw desert soil in North Las Vegas, Nevada in the Eastern Mojave Desert. Notice the color. It’s almost the same color as the rocket came from. There is no organic matter in this soil. Why? Because there wasn’t much growing in it to begin with. Why? We get 4 inches of rain in the Mojave Desert when we’re lucky and temperatures can reach 120° F (50C) Desert Soils Are Varied People think that all desert soils are the same. They are not. They are as varied as non-desert soils. Non-desert soils vary from dark chocolate brown and almost black to light brown chestnuts of the prairies. That brown color is a dead giveaway regarding the amount of organics in the soil, that is dead plant life that is rotten and you can’t see it anymore. Just the color remains for the eye to see. This is raw desert Sandy loam soil. From the color of it you can tell there is extremely little organics in this soil, a.k.a. O M or organic matter. As soil organic matter increases, soils become darker and less like the parent rock it came from. Two ingredients are needed to make this happen: organics and water. The color of this soil is because of a lack in rainfall and a lack of dead plants in the soil. A walk behind trencher was used to cut these trenches in the soil about 30 inches deep. Otherwise you needed a pick. These trenches will be filled with water and compost and then collapsed. Rainfall Adds Organics to the Soil (Irrigation = rainfall!!!) The soils in the Sonoran and Chihuahua deserts are vastly different from the Mojave. They are a better quality, they have more organics in them so they are a little darker brown in color, they are lower in salts, a little bit lower in alkalinity and they aren’t as problematic as Mojave Desert soils. In other words, you are less likely to run into pockets of toxicity such as boron, sodium and chlorides. Why? The principal reason why is because of rainfall. Compost and water was added to this soil and the trenches collapsed. The soil was allowed to dry until it was workable with the tractor and implements. The compost added to the soil covered the area 2 to 4 inches deep before it was cultivated as deeply as possible, usually 8 to 10 inches deep.Adding organic matter such as this compost to the soil will do nothing if water isn’t applied as well. Research from Desert Ag Stations If desert soil was previously in agriculture; that is, irrigation water was applied and plants were grown in it, then of course the organic matter content of that soil will increase year after year until it hits a plateau. Maybe that plateau might be 1% or even 2% but a far cry from the one tenth of 1% found in many of the Mojave Desert soils.Following research performed in previously irrigated desert soils may not give you the same results as planting in raw desert soil. This is the reason why some of the agricultural experiment stations in the desert come up with some different results when growing plants in desert soil. Knowing it is desert soil is not enough. You must also ask what the organic matter content is to get a good handle on how it will perform and how you must manage it. Compost is cultivated into the moist soil as deeply as possible, hopefully at least a 12 inches. Once a deep cultivation is done to this rod does soil, the compost is further mixed by using more cultivating tools. Water was added to the soil after the compost was added but it was allowed to dry until it was workable and the tractor and the implements did not compact it. Never ever cultivate a wet soil. That’s a big no-no.In small gardens double digging the plot helps in this phase. Mix Organics Deep and Thoroughly throughout the Soil Mix organic materials like good quality compost as deeply in the soil as possible. Remember, you will be growing root crops as well as asparagus which needs deep, well-drained soils. Rocks in these soils cause crooked carrots and crooked asparagus spears.The perfect soil for root crops is a Sandy loam with very few rocks in it. The final mixing of compost into this soil is done with the disc. In home gardens are Rototiller works just fine but don’t pulverize the soil. Stop when the organics are mixed and the soil is still “crumby”. Over tilling the soil or working the soil too much can cause it to turn to a powder and seal the soil surface making it difficult to irrigate and grow crops. Shaping the Beds For high-value crops and at high planting densities it is important to keep plants in separate areas from where people walk. One method is to use raised beds. The least expensive method is to create natural raised beds about three and a half feet wide without constructed side walls. It’s easy to do and not expensive. Let the soil maintain the edges of the bed rather than wooden 2 x 8s. Once the soil has been prepared it can be shaped into three and a half foot wide raised beds with natural sloping sidewalls. Walkways are created with a flat nosed shovel between the beds and throwing the prepared soil from the walkways on top of the raised beds. When the walkways are completed, a lawn rake is used to flatten the surface of the raised beds. For long raised beds I use a landscape rake. People walk in the walkways only unless they are planting or harvesting vegetables from the raised beds. Weeding, fertilizing and irrigation repair is done from kneeling boards with people’s tootsies only in the walkways. Raised Beds with Constructed Sidewalls Another method is to construct raised beds with sidewalls. Sidewalls can

Q. I have a mature palm tree that dropped seeds onto my lawn. Now I have hundreds of palm shoots growing out of the grass. I’ve tried weed and feed products, but they don’t kill them.  Can you give me any suggestions? Poem seedling pulled from the soil after germinating A. Palm seeds can live in dry soil for a long time. When they finally get water, they all germinate at once. Keep your lawn thick and dense by mowing high, watered regularly and fertilize it four times a year. Seeds that fall into it have less chance of getting established.             Try mowing palm seedlings. If the seeds come from a palm that doesn’t sucker from the base, there is a good chance that mowing will kill the palm seedlings. Many palms have a single, central bud at the top of its trunk and once it’s killed or removed the palm dies.             I know the task is daunting, but palm seedlings pull from the soil easiest immediately after an irrigation and when they are about 12 inches tall. try this tool to remove palm seedlings             As a last resort, try lawn weed killers that contain dicamba (Banvel) or triclopyr (Garlon) as part of the ingredients on the label. Both these weed killers control weeds that become woody. Use the highest rate permissible on the label. Mow the lawn first and then apply the weed killer.

Q. I’m growing bottle trees together with mock orange and roses and these trees drop their leaves in the middle of summer. What can I do to prevent this? Leaves on the ground beneath African sumac. One of the problems of African sumac is all the leaf litter it can produce in the middle of summer.Bottle trees can do the same thing. A. I am starting to think differently about bottle trees. I am beginning to suspect that, like African sumac, some trees drop their leaves when it gets hot and others don’t. Both of these trees originate from south of the equator in similar climates, one in South Africa and the other in Australia. Regardless, the best you can do is to prevent the soil from getting too dry and water trees 24 inches deep when you water. Bottle tree limbs can die back with sunburn. Bottle tree is not a true desert plant but it has thin bark that can’t handle a lot of direct intense sunlight. Both of these trees are not “desert trees” but they are used commonly in desert landscapes. Both of them will handle soils that don’t have a lot of organics in them so rock mulch is usually not a problem. This is not going to be true of roses or mock orange. Japanese mock orange doesn’t handle desert soils very well and will yellow if the soil is not improved at the time of planting, the soil is covered in rock for several years or if it’s watered too often and the soils begin to drown. They don’t come from the deserts of Japan. Leaf drop or leaf litter is a big problem in African sumac and I get a lot of questions about it. It can also be a problem in bottle tree. But it’s best to make sure the soil moisture does not drop too low or both of these trees will drop their leaves. Roses should never be planted surrounded by rock or this will result in about four or five years. They are not true desert plants, just like Japanese mock orange or bottle tree or African sumac Both roses and our mock orange (Pittosporum tobira) do not handle desert soils very well but they will tolerate a desert climate, high temperatures, low humidity.When I first moved to the desert in 1984, this plant had me confused with true mock orange which is actually Philadelphus coronarius. So we should differentiate between the true mock orange and this one which I prefer to call Japanese mock orange. Japanese mock orange comes from the same area of the world that gives us Japanese blueberry.If you have been following me and some of the problems with Japanese blueberry in a desert climate, then you will know you don’t want to put these plants with the name “Japanese” in front of it in desert soils in a desert climate or you’re looking for trouble. This is what happens to Wheeler’s dwarf Japanese mockorange one you put it in full sun, cover the soil with rock and water it every day or too often. Like I tell people, there is no such thing as the “deserts of Japan“. Okay, Japan has one but there are no plants there! So don’t treat it like a true desert plant. Both of them are not.Don’t get me started on Carolina cherry laurel and the deserts of North and South Carolina! (Except for Jockeys Ridge!) The default on your situation are the roses and Japanese mock orange. They like soils that are improved over raw desert soil which the bottled tree will be happy about. So cover the soil beneath these plants with at least 4 inches of wood chip mulch. Beneath the mulch spread a couple of bags of high quality compost like Viragrow’s Soil Pro. There goes soil Pro compost is a compost rich in nutrients. No fertilizer will be necessary for one to two years after applying it. Use a soil moisture sensor to help you judge when to irrigate again until you get it under your belt, and use a long piece of skinny rebar to make sure you gave these plants enough minutes. A skinny piece of rebar like this three sixteenths inch diameter is good enough to use for determining the depth of watering. Water small shrubs 12 inches deep. Medium-size trees 18 inches deep. Medium to large sized trees 24 inches deep. Really big trees 36 inches deep  The roses and Japanese mock orange can handle irrigation 12 inches deep while the bottle tree likes watered down to about 24 inches deep. If these plants are on the same irrigation valve, use drip emitters that are high-volume under the bottle tree and use moderate volume drip emitters with the roses and Japanese mock orange.