Q. I planted two Mandarin oranges from different nurseries this past spring.  One did very well in full sun from the git-go. The other had leaves that were turning yellow.  I applied iron and nitrogen fertilizers, but it didn’t do much after a week. So, I constructed some shade over at and it started looking green again. Sometimes plants need to “acclimate” to their new desert climate.   A. It sounds like you’ve got your answer; intense desert sunlight caused leaf yellowing. But it begs the question, “why only one of the trees if they were both mandarin orange?” You said the trees came from different nurseries. That might be part of the answer.             But first, eliminate other potential problems before I get to the nursery explanation. Make sure your trees share the same microclimate, the soil in both locations was similar with similar drainage, the soil mix used to plant both trees was the same, that the roots were kept moist and planted no more than half inch below the soil surface, that they were staked and watered thoroughly after planting. Sometimes yellowing on citrus can be for other reasons.             You may be observing differences in how and where your trees were grown versus our harsh, desert climate. A local nursery used to bring in citrus trees for sale in containers and put them in an area that had partial shade. They could put them in full sun and sell them from there, but they didn’t. Too risky. Sometimes yellowing can be from high light intensity.             Plants grown in a greenhouse, under partial shade or in a cool, coastal climate produce leaves that are different from leaves grown during our harsh desert sunlight and low humidity. When tender plants are plunged directly into our strong sunlight and low humidity, the leaves may scorch, yellow or drop from the plant. The plant is not dead but quickly produces a new set of leaves very different from its old ones. The newer leaves are smaller, thicker, tougher and better capable of handling desert sunlight and humidity. The plant has become “acclimated”. Yellowing from an iron problem happens on new growth and lowers the health of the plant making it more susceptible to heat problems.             Observe where nurseries are selling plants. Plants sold from shady areas may struggle when planted in full sun. Plants grown in a greenhouse need two or three weeks of “acclamation” before they are plunged into an intense desert landscape. This is true of vegetable transplants as well.             If you suspect you have a plant which may be acclimating to its new environment, sometimes it’s easier to strip off the leaves or prune the plant so its new growth is better acclimated to its new desert environment. In your case, wait until fall and remove the shade. Let the mandarin orange “acclimate” to its new home during the cooler fall weather.

Q.  We have lots of aphids in our good-sized oak trees that are dropping sap on our cars and the sidewalk. Short of cutting the trees down, do you have any suggestions on how to get rid of the aphids? Not from the reader but aphid sticky exudate on oak. A. Blame their high population number s this year on our wet and humid spring weather. The fastest and probably cheapest way to get rid of them is to drench the soil beneath the tree with a systemic insecticide diluted in a bucket of water. This dilution will help you spread it more evenly everywhere under the tree. aphids on pomegranate             The pesticide I’m telling you to use has the active ingredient imidacloprid in it. This insecticide is systemic so when you pour this around the base of the tree, diluted in water, the roots will take it up and transport it to the leaves. Since the aphids are sucking juices out of the leaves, they ingest this toxin and die. Leaf curl on plum from early feeding and leaf expansion             There are several trade names of this pesticide that contain imidacloprid. The most popular with homeowners is the Bayer product with the trade name “Tree and Shrub Insect Control”. Any product that you use must contain imidacloprid in the ingredients. The easiest and probably safest way to apply it is a “soil drench” but it can be sprayed on the leaves as well. One of the many products that contain imidacloprid. It is now the most used insecticide in the world.              The label will tell you how much of this pesticide is applied to one tree. Follow the directions on the label for a soil drench application. When you are finished with the application, rinse the bucket three times with fresh water and apply these “rinsates” under the tree as well. Wear unlined plastic gloves and eye protection when mixing and applying this product and rinse, or dispose of them, afterwards. Chitalpa black aphid             Consider spraying these trees during the wintertime, from top to bottom, with a dormant oil. Apply an extra dose to the base of the tree where aphids might be hiding. Dormant oil sprays applied during the winter are very effective in reducing the populations of aphids, scale insects and spider mites for the next growing season. Entrance to an ant colony on the orchard floor.             Ants love aphids. They “milk” ants of this sugary sap for their own use. If you look at the tree trunks carefully, you will see a steady stream of ants going up and down the trunk. They are also part of the aphid problem and should be controlled. Follow the stream of ants back to the opening of the underground nest. Sprinkle 10 or 15 “crystals” of ant bait directly at the opening of the nest. I use a product called “Amdro”. The nest will be empty the next day.

Join me in this episode of Desert Horticulture. I discuss the grasshopper invasion, those giant wasps that have been flying around and the fruit salad tree. Is it any good?

I received this recipe for pear tomato jam I thought might interest some of you.  For many years I helped my mother canning, storing, and making jams and jellies for a family of six. I finally quit making jellies about 4 years ago. I liked making jellies from strawberries and crushed pineapple; Apricot and pineapple; and Yellow Pear tomato with pineapple.   My own recipe: 4 cups tomatoes crushed ( I have a 30+ year old Oster chopper 1 8 oz can crushed pineapple Combine to make 5 cups of fruit (you may need a small amount of water 1-2 teaspoons lemon juice which keeps the jelly from turning dark 7 cups sugar 1 package pectin Follow the Pectin instructions. Keep up the good information Loretta

Join me on this Desert Horticulture Podcast where I discuss different methods of controlling aphids in landscape trees, using drip tubing instead of drip emitters to water landscape trees and how to use plants that don’t belong in the desert, in the desert. Join me as we discussed these and other topics in this Desert Horticulture Podcast. Download my podcasts from Google Podcasts, Apple Podcasts, Spotify, Stitcher, iHeart Radio, and Tune In + Alexa.

Q. I raised tomatoes for about 7 years and this year was my best year. The tomatoes that work best for me are Early Girl, Champion and Celebrity. This year I got about 200 tomatoes from these three plants already, they are still coming, and they taste good too. The only thing I did differently this year is put a 1-inch layer of worm castings on top of the soil. Was it the weather or the worm castings that did it or both? Worm castings is now a popular addition to raised beds for vegetable production.. Photograph complements of Viragrow, Inc. Las Vegas, Nevada. A. This may sound like heresy but there is nothing special about the fruit when using worm castings versus any good compost or quality amendment added to the soil. Some may argue but the tomato plant doesn’t know the difference. The important thing is that soil improvement was done.  But the overriding factor this year was probably the cool spring weather. Granted, you are managing your tomatoes better each year, the spring weather was cool for a long period of time, and you applied a good soil amendment and fertilizer in the form of worm castings. I think this is what everyone wants to accomplish when growing tomatoes, a high quality tomato that tastes good. This tomato was grown in Balkh Province, Afghanistan, where temperatures can rival the Las Vegas area. If they can do it, you can do it.             Repeat what you did next year and see if there is a difference in your production and the taste of your tomatoes. Hopefully, you took some good notes. I am guessing you will see a smaller number of fruit produced if the weather heats up in a hurry and there isn’t a long, cool spring like we had this year. And if you use a good soil amendment, like worm castings or a quality compost, the tomatoes should taste superb again. The Zimbabwe “Worm Man” who was selling worm castings that he was producing. Although the plants don’t know the difference, there is some scientific research that demonstrates some benefits to plants when using it.             Tomatoes stop setting fruit when air temperatures stay consistently above 95F. The tomatoes that set earlier continue to grow and mature when it stays hot. That isn’t the problem, It’s the production of fruit that stops at high air temperatures. That’s when the entire plant stops making more fruit. If you don’t have much room a tomato plant can be grown in a nursery container. I would recommend using a 15 gallon nursery container. When you are finished with production, this composted soil can be added to the garden or landscape. It makes crop rotation easy. Just replace the soil and container! Photo courtesy Viragrow, Inc. North Las Vegas.             If the air temperature drops below 95F for a couple of days, new flowers will again set fruit. They stop setting again once the air temperature returns above 95F. With air temperatures that fluctuate to the low nineties and then rise to the high nineties, tomato fruit production may be erratic. Fertilize tomatoes with a start up fertilizer at the beginning and don’t fertilize again until you start to see small fruits develop from the flowers.              Some other varieties of tomatoes to try include cherry tomatoes like Sweet 100, Sun Gold and grape tomatoes as well as the yellow pear tomatoes. These plants are reliable, quickly produce fruit from flowers and can fill some gaps when temperatures fluctuate a lot. Yellow parrot tomatoes, along with great tomatoes and cherry tomatoes are always successful in our climate. They don’t require a lot of production time from flowering to finish. Throw in a couple of these tomato plants with your others to help fill in the voids in production.             Also, choose tomatoes that are determinate in form rather than indeterminate. These tomatoes tend to produce larger numbers of fruit early in the season and don’t sprawl all over the garden. Pretty good information on determinate versus indeterminate             Include varieties like Better Boy or Big Boy and a Roma type like San Marzano for a “meatier” tomato. Move tomato plants to the other end of a raised bed rather than plant them in the same spot year after year. This helps reduce disease problems. Pretty good information on crop rotation             High temperatures produce a sweeter tomato and lower temperatures keep the acidity higher. Good flavor needs a balance between sweetness and acidity. The variety and weather conditions produce these delicate flavors unless the soil is void of plant nutrients.  Small amounts of mineral fertilizers work well if the soil has organics, like worm castings, added to it. Like this information? Visit my podcast and learn more! 

My soil moisture measurements for the University orchard were important. I used manual tensiometers and the Watermark Soil Moisture sensor. For a fast and fairly accurate idea of how wet your soils were these inexpensive soil moisture sensors are not bad. They are not accurate enough for publishing in scientific journals but for knowing if time to irrigate, its not bad. I have been mentioning quite often how to know when to apply water by using a soil moisture sensor. By sticking the probe in the soil near the middle of where the roots are located and taking a moisture sensor reading, you can roughly estimate the level of moisture in the soil. Here’s how. Chose a moisture sensor. This is an inexpensive soil moisture sensor you can buy from Amazon, Lowes, Home Depot and any local nursery. Its less than $10 and made for soft soils that are easy to push into but with some care how you use them you can make them last a couple of years of occasional use.   This one had a recognizable name from their compost thermometers but this one didn’t hold up in desert soils. The tip fell off after using it for three months. This is what happened to the Reotemp Soil Moisture Sensor after three months of occasional use. Maybe ten times. Maybe I got a lemon. 2. Adjust the sensor. The Lincoln and Reotemp both have an calibration screw on the backside. I stick the tip of the probe in a jar of water, let it get wet for about 30 seconds and adjust the meter so it reads “10”. I need a very small tipped screwdriver, like one a jeweler uses, to make the adjustment. I do this every time I go out and take measurements. Here I am inserting the tip of the probe into a glass of water, waiting about 30 seconds and then checking to make sure it reads “10”. If not, which is often, I adjust the sensor to read 10 by turning the adjustment screw on the back until it reads “10”.  Some of the inexpensive plastic types may not have anything to calibrate. In cases like that, I make a note of what number it reads when the tip is inserted in the glass of water and make a mental adjustment to my measurements in the field. 3. I always take three measurements near the same spot. This is because the soil is not the same due to the variability of the soil in the field and rocks. I insert the tip of the meter into the soil, slowly, until it reaches about halfway of the depth of the roots of the plants. Sometimes I have to do this four or five times to get a good measurement due to rocks. For instance on new fruit trees the depth it is inserted is maybe only four or five inches. But I watch the needle move as the tip is inserted deeper. For established trees I will measure the soil moisture at about 6 to 8 inches. Average readings of about “5” tell me its time to irrigate. 4. I use rebar to tell me how deep the irrigation water is draining. I use 3/16 inch rebar, four feet long, to tell me if I watered deep enough. The irrigation depth of plants should be 8 inches for annual vegetables, lawns and annual flowers. For small shrubs and perennial vegetables like artichokes and asparagus it is 12 inches. For medium sized shrubs and small trees, 18 inches deep. Medium sized trees 24 inches deep. Large trees like many pines, 36 inches deep. by pushing on the rebar into wet soil it will be hard to push where the soil is not wet. For large trees you need a four foot long rebar. To change the depth of irrigation on the same valve, change the size and number of emitters to the plants not getting enough water. 5. Irrigation water should be applied to AT LEAST half the area under the plant canopy. If the plant is three feet wide then four emitters placed 12 inches from the main stem is enough. If the spread of a tree is ten feet, then place a circle of four emitters 12 inches from the trunk and a second ring of emitters 18 inches beyond that. I doubt people will water the entire area under the canopy. The area under theis tree needs more drip emitters and the emitters spaced closer to get enough water applied and to the right depth. 6. Mulch slows loss of soil water from evaporation and makes plant roots more competitive. Mulch will add one to two days extra between irrigations during summer months. Apply woodchip mulch 3 to 4 inches deep to soils beneath plants that are not native to desert areas like these fruit trees. Rock mulch can be used 2 to 3 inches deep to cover soils beneath desert plants. But my experience is that even desert plants like woodchip mulch. 

Learn how to irrigate landscape plants, fruit trees, vegetables and your lawn in this episode of Desert Horticulture.

The most critical plant management issue when growing plants in the desert is how much water is enough, when to apply it and where to apply it. Drip emitters are watering but there are no plants! Water where plants are located and if they are removed, don’t forget to stop the water. Secondary to this issue is how well the soil surrounding the roots hold onto the water or release it when the plants need it. In short, how much water should the soil hold and how much should it let go? (drainage). How Plants Use Water Plant roots take water from the soil and send it to the leaves. As plants get bigger, they have more leaves so their need for water increases. Plant roots are always trying to find more water. They may not go looking for water but they can find out where it is!  Roots don’t respect property lines. If trees find water, they grow in the direction. Plants always try to become bigger. This is why plant roots grow into new areas of the soil where there is water. These new sources of water are tapped into by the growing plant roots. These new sources of water become very important to the plant as it gets bigger.  When soil fills with water, it drains. The water that drains from the soil leaves voids in the soil that fill with air. The ideal landscape soil holds on about 50% of the applied water but if there’s too much, the soil releases it so the roots can “breathe”. This is called drainage. In the ideal landscape soil, about 50% of the applied water escapes the soil as drainage. The end result after drainage is complete is about half of the soil holds on to water while the other half has released it and these places are then occupied by air. One gallon of applied water to dry soil = 1/2 gallon remains in the soil and 1/2 gallon drains. An ideal soil has about 25% water and 25% air between its soil particles. Two Ideas About Watering  There are two methods floating around about how to water.  Gas Tank Method. Some advocate filling the soil surrounding the roots with water and letting the plant “drink” from this pool of water until it needs more. Think of it like filling a gas tank on a car. The gas tank is filled and you drive around as much as you want but you refill the tank when it’s about half empty. In irrigation lingo, many plants are watered again when about half of the water held by the soil is gone. It’s different in cars. Gas tanks are filled with fuel when its about three fourths empty or more. Allowing plants to use three quarters or more of the water in the soil, like a fuel tank, would kill most plants except cacti! One gallon of applied water to dry soil = 1/2 gallon remains in the soil and 1/2 gallon drains. One quart of this water is used while one quart remains in the soil. The Daily Sip Method. The second idea about how to water gives “sips” of water to plants every day. People who follow this idea give plants a drink of water every day. These drinks of water are more often in the summertime and less often in the wintertime. Also, these drinks of water are taken more often in the summer months than the winter months. This isn’t like filling a gas tank at all. This is more like drinking a glass of water. In the summertime you drink water more often and in the wintertime you drink water less often. Every day give plants a “sip” until the plant uses one quart. Pluses and Minuses of Both Ideas Gas Tank Method. The first idea, “filling the gas tank” lets the plants “drink” from this supply of water any time it wants or needs to. The easiest water for the plant to get is the water closest to the surface of the soil. When water is plentiful in the soil, plants drink from it luxuriously and greedily. Unfortunately, the plant must compete with evaporation of this shallow water into the air. Both the plant and the air are “tugging” at the same shallow source of water.     Water was applied to fast for the soil to hold all of it or the soil couldn’t hold anymore. When the gas tank drops to maybe three quarters full, the plant drinks from it a little bit more, cautiously. It taps into water that is a little deeper in the soil. It’s harder for the plant to take water from the soil when the soil holds on to it more tightly. As the available water in the gas tank drops to 50%, the plant finds it even more difficult to get water and tries to find this water in still deeper soil. But the plant is still “happy”. This mesquite tree is growing about 50 feet from a river. Its roots are growing deep because it of soil moisture from the river. When this water supply in the soil, or gas tank, sinks to about 40% or less of the original amount, then that’s when we begin seeing many plants starting to wilt during the hottest part of the day. This is our visual indicator that the plant can’t get enough water for its leaves and newest stems. This can lead to permanent wilting; there just isn’t enough water in the soil that the plants can find. Mid day wilting of vegetables on a hot day. They will recover when it gets cooler but growth may be lost today. A side note. Sometimes plant wilting is not because there isn’t enough water available to the roots. It can happen when the air is so hot and dry that it’s pulling the water from the leaves faster than the roots can find it. This can happen

Join me in this special podcast on growing tomatoes in the desert if you ever wanted to try or just moved to the desert.