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.

Tomatoes are tricky in Las Vegas, but they typically don’t die suddenly, to get them to produce well. The idea of KISS (Keep It Simple Stupid) is always a good plan when doing something for the first time or when you move to the desert from a wetter place. That’s the end result we all want…big, home grown tomatoes. These were tomatoes grown near Mazari Sharif, Afghanistan. If they can do it, YOU can do it. KISS steps for tomato growing: Plant in early spring, Feb 15 or later depending on the weather and weather forecasts for the next two weeks. Local tomato transplants are usually okay. Sometimes you can plant early and get away with it and sometimes not. If planting late, pick cherry, grape or yellow pear types. Always use a “determinate” tomato until you want to experiment. Start with 15 gal nursery container and fill it with potting soil for your first tomatoes. Dont use a smaller container than 15 gal.  Select varieties that are known good producers; Champion, Early Girl, Patio, Jet Star, Roma for full sized tomato fruit. For smaller fruit choose cherry tomatoes such as Sweet 100 or grape tomatoes or yellow pear. They are very reliable. Select transplants that are about 6 to 8 inches tall and healthy. Avoid large transplants. Select small transplants for the container. These transplants have a surface mulch of pine animal bedding around them to keep the soil most but you wont have to have it if planting in the cool spring months. Pick a soil mix and not potting soil, compost, or something similar. It should be somewhat heavy and not light weight. Maybe in a couple years you can play around with different soil mixes but not at first. I am holding Viragrow’s Premium Garden Soil Mix. It is mixed about 1/3 compost and 2/3 sand plus some seaweed extract, rock dust and some other goodies. You dont have to use something this full of stuff but having the soil heavy and well drained helps establish transplants and is forgiving if you are not sure of your desert irrigation talents yet. Try planting in new, 15 gallon containers first before going to a raised bed until you get the knack of it. Use an established soil mix known for growing tomatoes in the desert in the past for vegetables. Fill the container from the bag and then water it thoroughly so that the soil settles leaving a 1 inch headspace at the top. Locate them on the east side of a wall or building. This is a five gallon plastic nursery container and it will work but the 15 gallon container is more “forgiving”. It holds more soil so it doesn’t run out of water as soon and doesn’t heat up as fast. This next part is a bit tricky. If the soil mix did not have any fertilizer in it, then water with a starter fertilizer mixed in the water used for watering. This can be a small bucket or can. This is a water soluble fertilizer that can be dissolved in water and watered in the soil just after you plant. Its nitrogen content (the 15 on the left) is lower than the middle number (30) which is phosphorus. When planting transplants or seed it is important to have more phosphorus available to the plants than nitrogen. This helps get their roots off to a good start. The 15 on the right, potassium, is ALWAYS a good idea to have in a fertilizer. ALWAYS. Fertilizers used for getting transplants and seeds off to a good start are fertilizers like this Arizonas Best Starter Fertilizer. It is a granular fertilizer that is mixed with the soil before planting. Plant in this soil when it is moist. The first time you water, use water with a starter fertilizer in it. Use a clean digging device like a garden trowel. Remove the transplant from its container even if it’s a peat pot. If an expandable peat pellet was used with that netting on the outside, slice or cut the netting in several places until it nearly falls apart. Do this even if they tell you, you don’t have to. Plant it at the same depth it was in its old container into its new container and water it in until water comes out the bottom of the container. If there is no container, water it in until its muddy. Do this two more times in the next 24 hours. Buy a soil moisture meter used for houseplants. It should cost less than $10. Stick the end in the soil about one inch and water next time when it reads 5. Use that soil moisture meter to tell you when to water until you feel the watering rhythm. If you aren’t sure if its time to water, use the soil moisture meter to tell you. Soil moisture sensors like this one intended for houseplants will work in our soils but dont last very long. They fall apart after a few times. If you applied a fertilizer when you planted the transplant, don’t apply any fertilizer until you see small fruit that formed from the flowers. Then start applying fertilizer, lightly, once a month. Tomato fruit setting (right) and the flower open and ready for pollination (left).

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