Desert Horticulture Podcast: Producing Fall Tomatoes

Learn how to produce tomatoes in the Fall in hot desert climates.

Plant Acclimation Necessary for Vegetable Transplants in the Desert

Q. I had three tomato plants, all started from seed. They were all very healthy and thriving beautifully. They were planted in a grow box filled with growing media. After about 5-6 weeks the leaves started curling up on all three plants and after about 2 weeks all plants died. When I first noticed the problem, I looked it up on the internet and it informed me it was a watering problem but not to worry. I didn't worry and they all died.

A. I don’t know if you saved the seed from other tomatoes or you bought the seed and where you bought it. I also am not sure if they were grown as transplants in the home and then moved directly into the garden.

Acclimating transplants (hardening off)

 If these tomato plants were grown from seed inside the home and then moved into the garden, they need to be acclimated to the weather before planting. Inside a home or greenhouse there is protection from intense sunlight, higher humidity and very little wind.

 Acclimate your seedlings to our weather by putting them outside in light shade or the east side of a building. After two or three weeks and you see some new growth, they are ready to go into the garden. Some old-time gardeners will put a wooden shingle on the south side of the plant to give them some protection for another couple weeks.

We used to use coffee cans too. Acclamation helps plants adjust to our desert climate and weather conditions. They go through a lot of shock if planted directly into a garden or grow box from inside a home or greenhouse. Sometimes planting them directly from a protected environment into the garden will cause them to die.

The other possibility can be watering too often and poor drainage. If the soil stays too wet and the soil does not drain water easily, the roots can rot and the stem can develop collar rot. It looks like they aren't getting enough water so most people water more often. Big mistake. The soil needs more amendments and the transplants watered less often.

Roses and Intense Heat

Q.  All my roses face north, and some are against a cinder block wall. They get no shade and they really struggle with our summer heat. Most will have to be replaced. I am already looking at roses to plant for next summer. Do you know any varieties that can withstand our summers? Also, how does Crepe Myrtle handle our summer heat?

A. If your roses are on the north side of a building then they may get direct sunlight late in the afternoon because of where the sun sets in the summertime. That late afternoon direct sun can be very damaging if they have been going on the shady north side all day. Healthy plants handle heat better. Plant both in soil amended with good compost.

Roses growing in the desert should not be planted surrounded by rock.

            Somewhat tender plants to our desert climate, like roses and crape myrtle, handle the intense desert heat and sunlight if they are growing in soil amended with organics and the soil is covered with mulch that rots or decomposes. Roses and Crepe Myrtle will struggle after a few years when planted in soils covered by rock. If you want them to look good in years to come, roses and Crape Myrtle should never be surrounded by rock mulch. Ever.

            Always plant in soils that are amended with a decent soil amendment like compost. After planting, always cover the soil with mulch that rots or decomposes such as woodchips. The woodchips on top of wet soil will decompose. Fertilizing these plants appropriately keeps them healthy, the leaves green and vibrant.

            It might be a good idea to provide some shade from that intense sunlight late in the afternoon. Plant a medium-sized shrub or build a pony wall in this location to provide a less intense microclimate for their growth.

            A list of roses that perform best in desert climates can be found on the Weeks Roses website located at www.weeksroses.com in the column titled, “Roses by Climate”.

Murcott Mandarin Orange Growing Problems

Q. I have several fruit trees planted around my fire pit near a waterfall and pond.  I bought a Murcott tangerine which has not grown an inch in 2 ½ years and the tiny fruit it produces falls off by summer. All the other fruit trees are doing fine except for this tangerine.

Murcott mandarin orange from reader

A. This citrus produces fruit ready to harvest from January through March. It originated from central and southern Florida and does best in locations where freezing is rare. Any freezing temperatures during the winter and early spring may cause the fruit to be inedible. I hope it’s planted in a warm microclimate.

Same Murcott Mandarin orange. 

            Problems like these, when similar plants are growing together and one does poorly, is usually a problem with the soil or how it was planted. Possibly irrigation. During the winter carefully lift the tree from the ground by severing the roots with a sharp shovel and lifting the rootball with two shovels on opposing sides. Gently wash the soil from the roots and put the tree in a clean bucket of water, covering all the roots with fresh water.

Citrus Harvest Dates University of Arizona

            Re-dig the hole so that it’s five times wider than the tree roots taken from the ground. If water drainage was a problem, the tree should be planted about a foot higher than the surrounding soil. Do not use the same soil but replace it with a soil mix amended for planting.

Murcott Orange Info UCR

            When planting the tree in this hole, the roots should be less than ½ inch below the finished soil surface surrounding the tree. As soil is added around the roots, add water from a hose to remove any air pockets. Do not step on the soil with your feet but use water to settle it around the roots. Remove about one third of the canopy of the tree after planting. Stake the tree so the lower trunk doesn’t move for one growing season.

            If the soil mix was made with a rich compost, no fertilizer is needed for one or two growing seasons. Otherwise, apply a fertilizer to the soil high in phosphorus when planting. Next spring place fertilizer 4 inches below the soil and about 12 inches from the trunk with a shovel and water it in.

Reason Why Melons Split Before Ready

Q. A second crop of mini-melons I planted split before it was ready to harvest. I think it was the heat because the first crop using same seeds ripened on the vine. These have a mild taste but not very sweet. Is there a "sow by" date so they will ripen before it gets so hot?

A. Melons split before they are fully mature because the soil becomes dry and then watering or rain occurs. The result is burst or split fruit because the fruit swells. This happens with many kinds of fruit, not just melons. The seed inside the fruit may be mature but the fruit hasn’t yet finished ripening before it splits.

Blood orange fruit split

            When a plant is not getting enough water, but the soil begins to dry, the fruit will either abort early or the plant will try to finish as much ripening as possible before the water runs out. This early ripening due to a lack of water can affect the sugar content or its sweetness, the quality of the fruit, the size of the fruit or all three!

Kara Gul pomegranate split and interior rotted

            When the plant is not getting enough water and begins ripening the fruit, but the soil gets extremely wet again, water is pumped from the roots into the fruit and it splits. The fruit might not be fully ripe, but the seeds are oftentimes mature enough to grow. Applying a thin surface mulch to the soil or growing a variety that shades the soil better and retains soil moisture may reduce fruit splitting during the heat. Also, using a plastic mulch when growing vegetables helps retain water in the soil and reduces splitting.

Myers lemon fruit split

            The sweetness or quality of the fruit depends on many things, but weather and climate are major factors. In fruit and wine culture, this is called the “terroir” of the crop. Therefore, some varieties of fruit produce better quality fruit than others in the hot desert versus coastal California. Try a different variety of mini-melon next time, particularly one that has parents which performed well in hot climates.

Nubiana plum fruit split

            Most of the seed packets tell the days to harvest. If the soil is kept moist, the days to harvest should be accurate. However, add five days to this number if harvesting a fall crop that is normally grown during the spring and summer months. 

Desert Horticulture Podcast: Why Fertilizers Might not Perform Ideally in Desert Soils

Join me in an explanation about the role of organics in desert soils and their impact on applied fertilizers.

Butterfly Bush is Not for the Desert but Needs Extra Care if Done

Q. We planted a butterfly bush that was doing good but suddenly took a wrong turn! I’m very grateful for any help and guidance!

Sorry. I dont have a picture of a butterfly bush growing in the desert.

A. There are problems, sometimes, using the common names of a plant. Do me a favor and Google “butterfly bush”. If what you are calling butterfly bush is “Buddleia”, then you have a bush that struggles in hot desert climates unless you keep it out of the afternoon sun. You must improve the soil around this plant at planting time and never plant it in rock, a.k.a. desert landscapes.

            This is a shrub that grows well in Chicago, Illinois. It can be planted as far south as Atlanta, Georgia, so it probably will flower this far south, but I have never heard of it planted in the hot, desert Southwest. In our climate, plant it on the east side of a building where it gets shade in the afternoons. If you planted this shrub in the wrong spot, baby it through the heat of the summer and move it to a new location in October.

            Plant in soil amended with compost. Use woodchips at the base of this plant in a circle at least six feet in diameter. Water it to a depth of 12 – 18 inches and use 4 to 6 drip emitters after it becomes established. Two emitters should be enough for the first two years. Watering frequency would be the same as fruit trees and other non-desert landscape plants.

            This shrub is beautiful when it flowers. It flowers on new growth so it’s best if it’s pruned to the ground during the winter of each year after it is established. Its floral display depends on the plant vigor, fertilizers applied and its overall health. Apply iron fertilizer along with a fertilizer used for roses in late fall just before leaf drop or very early spring.

Drip Tubing Can Be Used for Watering Trees

Q. I was thinking of using soaker hoses around my trees instead of drip emitters. Any advice on that?

Drip tubing has emitters embedded in the walls of the tubing.

A. You are calling them “soaker hoses” but I prefer to call them “drip tubing”. Drip tubing is about half inch in diameter with drip emitters embedded in the tubing walls during its manufacture. Its best use is in areas that need water applied evenly to the same depth, repeatedly.

Drip tubing emitters release a precise amount of water at precise distances apart.

            Drip emitters are added to “blank tubing” (no emitters in the sidewalls) after it’s installed. It’s best for watering individual, smaller plants with spaces between plants that should stay dry. Drip emitters are best for watering different kinds of plants of different sizes with varying amounts of water.

Drip tubing must be under a precise pressure, psi, to work properly.

            Drip tubing is ideal for watering trees over 20 feet tall. A coil of drip tubing can be placed under the canopy of a tree and enlarged as the tree gets bigger. The embedded emitters in drip tubing should be 12 to 18 inches apart under the canopy of the tree. The length of tubing needed depends on how much water is applied. When water is applied under medium trees, it should penetrate 18 – 24 inches deep. When water is applied under large trees, it should penetrate 24 – 36 inches deep.

Citrus Can be Tender in Desert Climates

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.

Controlling Ants in Oak Tree

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.

Desert Horticulture Podcast: Grasshoppers, Giant Wasps and the Fruit Salad Tree

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?

Jelly from Yellow Pear Tomato by Reader

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

Desert Horticulture Podcast: Aphids, Drip Irrigation for Trees and Butterfly Bush

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.

Successfully Grow Tomatoes in the Desert

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! 

Watering Pine Trees – Water Deep!

Q. I recently moved into a condo that has pine trees on the property. Some of them look like they aren’t growing much but those still in grassy areas look much better. Some other pines have branches that are dying back. Do I need to supply water to these trees?

The very new growth in the spring of pine trees are called "candles" because they look like candles. All the new growth for that pine tree is contained in that candle. If water is available to the tree, candles will stretch and get big. If water is limited, the candles will not stretch and the new growth will stay small.Notice the buds at the base of the candle. I will talk about these buds in the next picture.

A. All of this is not simply a water issue. There is probably a disease problem going on as well. But first things first. Pine tree branch growth, and how dense the tree is, has a lot to do with how much water it receives in the spring and early summer months. Just as important is how deep the water drains in the soil, to encourage deep root growth, after it’s applied.

Branches of pine trees are in the whorls along the trunk. In the picture above, you can see the buds at the base of a candle. Those buds will grow into limbs that are in whorls around the trunk.

            Most native pine trees grow along canyons or stream banks where water is plentiful in the spring months and less available later in the season. Water availability coincides with spring growth which in turn increases the tree density.

            Water pine trees deeply, particularly in the spring months. How deep? Water should drain 24 to 36 inches into the soil each time it’s watered. To make sure it’s deep enough, measure this depth with a long thin metal rod like a piece of rebar. Plenty of water this time of year helps push new growth. This new growth supports the needles responsible for a dense tree canopy. Deep irrigations are important later in the year, but less often, to maintain this density.

This blow over can happen to trees when they receive shallow irrigations and shallow applications of water. This is a mesquite but it can happen to pine trees, and does. Water large trees deeply to avoid blow over during strong winds. With deep irrigations, roots will grow deeply.

            Lawn watering only applies water about eight or 10 inches deep. This is not deep enough for large pine trees as they get bigger. Watering lawns with shallow irrigation may keep the trees denser but it doesn’t encourage the deep roots needed during strong windstorms. Besides the lawn water, large pine trees should get periodic deep watering as well. Pine trees in lawns may look full but they usually will blow over during windstorms as they get bigger.

Aleppo Pine Blight is classified as a disease but there is no known pathogen or living disease agent associated with it. In extreme cases it can cause entire branches to die. But the tree with this problem should be and Aleppo Pine, not a different type of pine.

            Branch dieback of pine trees is usually a physiological disease that cannot be cured called Aleppo Pine Blight. In most cases, new pine needles in the spring replace the dead needles lost during the winter months.

When to Plant Pomegranate

Q. We are thinking of planting a pomegranate bush in our backyard. I suppose right now in the middle of summer is not a good time to plant. Would late September or early October be okay, or do we have to wait until Spring? Any other helpful hints on planting this type of bush?

Pomegranates grow well in hot, dry climates that have winter temperatures that don't fall below about 20° F (-7 C). Pomegranate can develop several disease problems that affect the quality of the fruit in humid climates. You start to see some winter damage to pomegranates starting around 20° F. Some varieties can handle colder temperatures in the winter than others.

A. Summer months, when it’s hot, is not the best time for planting anything except palm trees and Bermuda grass. Pomegranates will struggle after planting during the summer months. To attempt summer planting, you better have a very green thumb and lots of experience gardening in the desert.

Pomegranate flowers form on "current season wood". This means that the flowers form on the wood formed that year. This is why pomegranate doesn't start flowering until a little bit later in the season than peach or apricot trees. And pomegranates continue to flower through most of the summer.

            Wait until Fall, about mid Sept to mid Oct in southern Nevada. You will have more success during the Fall months and the plant will be happier. A disadvantage is that the selection of local plants is not as large as in the spring months. Probably the two most popular pomegranate varieties are the traditional Wonderful or the sweeter and soft seeded Utah Sweet variety. If you don’t see what you want, wait until spring.

The Ambrosia variety of pomegranate is one of the earliest varieties with it fully ripe and ready to pick in about September. Ambrosio generally forms fruit larger than this one.

The fruit inside, called arils, is about the same color as the outer skin or rind in Ambrosia. That might not be true in many varieties.

            If you must plant now, do it early in the morning and have the hole already dug and the soil used for planting amended with compost. Fill the hole with water the night before and let it drain overnight.

Maintain the old wood of pomegranate and the percentage of larger fruit will be higher. Some of the more popular varieties include Wonderful, Sweet, Eversweet, Grenada and Sharp's Velvet. A variety recently released in the United States called Parfianka is getting a lot of attention lately.

            When planting, soak the container in freshwater for about 30 minutes. Take it out of its container and immediately place it in the hole and start filling the hole with water. Add the amended soil to this slurry and let it flow around the plant roots.  Stake the plant to keep the roots from moving and water the entire planting hole thoroughly so it’s muddy. Water it again, just like that, the next day. Set the irrigation controller so that it waters not more often than every other day during the heat. 

Why Oleander Not Flowering

Q. I have a dozen, full-sized oleander plants I put in last year. I fertilized them with a 20 – 20 – 20 fertilizer. They are growing great but they rarely flower. Am I missing something or is it the fertilizer?

Flowers of a full sized oleander shrub. Flowers grow on "current seasons wood". In other words, the flowers form on stem growth this year, not last.

A. It will probably take about three years for them to really start flowering a lot with that fertilizer and regular irrigation. Oleander loves irrigation water. It also loves fertilizer. The combination of regularly watering and applying a good fertilizer results in dark green leaves with lots of new succulent growth. This new growth is not yet fully mature. When it does flower a little bit later in its life, the show will be spectacular. Just be patient.

If oleander is cut back hard, it will grow fast to reach close to its size before it was cut back. Some people call this its "root to shoot ratio". When the plant has an existing large bunch of roots and the top is removed, the sbrub grows very rapidly until it gets back close to its original size. It doesn't waste time and energy flowering yet. But it will when it gets larger.

            The nitrogen in the fertilizer is the first 20. The second and third 20s stand for the phosphorus and potassium in the fertilizer. The middle 20, the phosphorus, encourages flowering but it also encourages the roots to get firmly established in the soil. Flowers will be produced on new growth. The more stems of new growth, the more flowers it produces. If the oleander is lush and bushy, it will be full of flowers and bloom when it’s ready.

Dwarf oleanders stay small and flower at a smaller size than standard sized oleanders. When oleanders are young make sure there is plenty of phosphorus in the amended soil and then just feed it nitrogen fertilizer to get it big. This shrub will start flowering when it's supposed to.

Soil Moisture Sensors are Not All the Same

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. 

Desert Horticulture Podcast: How to Irrigate Plants Growing in the Desert

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

How to Water Plants in the Desert

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 to vegetable transplants with tops growing too fast for their roots to send water to the leaves. It can also happen to newly planted fruit trees, shrubs and landscape trees. When this happens, it is called temporary wilting. As plant roots become established in the soil, temporary wilting may disappear.

Lettuce growing in plastic and straw mulch in Kosovo.

Another side note. Can you see the value of a surface mulch? Mulch is something applied to the surface of the soil that slows down the loss of water from the surface to the air, i.e., evaporation. When surface mulch is applied such as woodchips, rock or even plastic, evaporation slows down tremendously, improving the odds that plant roots will outcompete for the same water.

 

Plants growing in desert soils may grow better if woodchip mulch is used instead of bare soil or rock mulch.

The Daily Sip Method. The second idea, where daily sips of water are given to plants, requires regular, and sometimes daily inspections of plants. To do a good job using this idea, you should be very familiar with how much water different plants need. Otherwise plants receiving the smallest sips of water will dictate when to apply water to other plants. When these underwatered plants show signs they are not receiving enough water, they force us to apply water to all the plants receiving water at the same time as they do. 

This type of watering can be very wasteful and result in those plants, already receiving enough water, to get more. Hand watering plants not receiving enough water, instead of using the irrigation system, can reduce landscape water use and your water bill. But its time consuming.

A side note. Another drawback to this idea of watering is the encouragement in the growth of shallow roots on plants. Not terribly important with small plants, but when irrigating large trees this type of watering encourages plant roots to grow near the surface of the soil. A major reason for deep roots of trees is to prevent them from blowing over during strong winds. This type of watering encourages shallow roots to form on large trees. The formation of  "sip watering" and the formation of shallow roots leads to the blowing over of large trees.

This mesquite tree, (roots can grow to 200 feet deep!) blew over because it was irrigated with flowers and a lawn which makes shallow roots.

What's the solution?

1. Use the "gas tank method" when watering plants. The size of "gas tanks" depend on the size of plants irrigated. Vegetables, lawns and annual flowers require watering to a depth of 8 to 10 inches. Small and medium-sized shrubs and perennial vegetables should be watered 12 – 18 inches deep. Small and medium-sized trees should be watered 18 – 24 inches deep. Very large trees should have water applied 36 inches deep.

2. Use a soil moisture meter for knowing when to water again. Inexpensive houseplant moisture meters can be used for annual and perennial vegetables, lawns, annual flowers, small shrubs and perhaps even small trees and fruit trees. For larger plants, purchase and use a more expensive soil moisture meter. Measuring the moisture in the soil near the plant roots can give you an idea when the "gas tank" is approaching 50% full and it's time to water.

Moisture meters can be under $10 and others less than $100. For a few uses and shallow depths, choose the $10 version and be preparted for it to be thrown away after a time. They all have a gauge reading from 0 to 10, Dry to Wet.

3. Use a thin metal rod, like a 4 foot long piece of rebar, to determine how many minutes are required for an irrigation to deliver enough water to fill the gas tank. This metal rod can also be used to determine the size of the drip emitters (gallons per hour) needed to deliver that amount of water.

 A stick of rebar can be used for judging how deep water is draining.

4. Water the area under the plant to at least half the area under its canopy. For small plants this might mean using two emitters, medium shrubs four to six emitters, small trees and large shrubs 10 to 12 emitters and so on.

Water the soil under the canopy to AT LEAST half the area under it. This is not enough.

5. Apply mulch to the surface of the soil. For desert plants, rock mulch can be used. For non desert plants consider using woodchips. Vegetables will benefit from plastic mulch to warm the soil and keep it moist.

Rock mulch conserves moisture too. It just doesn't add anything back to the soil like woodchips can.

Did you like this information? Visit my podcast on this subject and learn more!