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Monday, June 10, 2019

Leaf Color in African Sumac Speaks Volumes

Differences in trees can be because of their genetics and how they were propagated in the nursery, differences in soil in very small areas and management.

Q. We had 3 African sumac trees planted in our backyard 1½ years ago. We treated them the same during this time but the tree the farthest away has large dark green, healthy leaves and the other 2 trees have lighter color leaves and they are curled. 

A. African sumac is propagated from seed so there is a lot of variation among trees. They also come in male and female trees so let’s remember that as well.
Seeing seed pods in African sumac is a good indicator the tree is female.

            Lighter leaf color can mean the trees are not getting enough nitrogen fertilizer, they are watered too frequently, or the soil does not drain water quickly enough. Because these trees were not planted by you, it’s not known if the soil where these trees are growing drains water similarly or not.
            Let’s tackle the fertilizer issue first. Apply a high nitrogen fertilizer in the basin of the trees just before an irrigation. Let the irrigation water transport this high nitrogen fertilizer to tree roots. If nitrogen fertilizer is the culprit, you should see a change in the leaf color before one week.
Moisture sensors like this inexpensive type used for houseplants can tell you the approximate time to water. Push the probe into loose soil in several places to get a rough idea when the soil is wet or dry.

            Inexpensive soil moisture meters, such as they use for house plants, can give you a rough approximation if the soil is wet or dry and when to irrigate again. Water these trees only when the soil is beginning to dry, never while the soil is still wet. If trees are watered too soon and the soil is still wet, leaves can discolor and become yellow rather than dark green. But the differences in leaf density between the trees indicate a difference in the amount of water they are receiving.

Leaf Drop on Apricot Reasons Why

Leaf drop on any tree can happen if the flow of water from roots to the top is interrupted.

Q. We have a five-year-old apricot tree. Previously, it’s always seemed happy but this year it leafed out beautifully, then it started dropping its leaves. Apricots are still on the tree but not developed yet. Then this week ½ of the branches on one side are leafless.
Another angle of the same tree.

A. Pictures were sent to me of this tree so let me explain what I saw. The apricot tree is 6 to 8 feet tall with a similar spread but leaning strongly toward the light but away from some taller shrubs on one side. Leaves are on the ground and have dropped from the side away from the light. The week it dropped its leaves was a hot week and then it got cool again.
Apricot sap dripping from limbs or the trunk can be a sign of borers particularly if you see it when it gets hot.

Trees drop their leaves because they are not getting enough water. They also drop leaves if it’s too dark, but I think in this case it’s a water issue. A lack of water can be from not enough water applied to the soil under the tree, borer damage in the trunk or several large limbs or a disease problem.
Sap dripping from the trunk can indicate wet soils. Add lots of water and then hold off watering until the soil has begun drying.

            I’m going to rule out the disease possibility because it is highly unlikely in the desert. Borer damage is a possibility except the leaves are dropping at the wrong time of the year and from half the tree instead of a branch. Borers cause leaf drop during the heat of the summer, June or July, frequently affecting an isolated branch or two. So, let’s rule out borer damage.
Wood chip mulch applied several inches think is good for fruit trees planted in desert soils but keep the wood chips a foot from the trunk for the first few years to prevent collar rot. Collar rot on fruit trees looks alot like drought.

            It is possible this tree had gotten larger and was not getting enough water. Along with a shortage of water, the distribution was not over a large enough area under the canopy to satisfy its roots. As trees get larger, they require more water distributed to a larger area under the canopy.
            To test this idea, use an inexpensive sprinkler on the end of a hose, connected to a mechanical timer at the hose bib or faucet. Put the sprinkler about 2 feet from the trunk of the tree and turn on the mechanical timer for two hours so it wets the soil deeply in an area about 5 feet in diameter. Do the same thing to the other side of the tree. Do this twice a week for the next two weeks and let’s see if the tree responds.
            If I’m right, you will see new growth coming from the limbs that are bare and where there are leaves, you will see new growth. If this is the case, increase the number and size of the emitters. Place one drip emitter scattered about every 2 feet under the canopy of the tree. The water should penetrate the soil about 18 inches deep after an irrigation.

Magnolias Need Special Locations and Management

Q. I have two dwarf magnolia trees in my courtyard in front of the house. They started dropping leaves and they’re kind of scarecrow looking. What do I do?
The Mojave Desert is not the easiest place to grow magnolias. Magnolias, Southern Magnolias in particular, will have difficulty growing in a desert climate.

A. Let’s get something out of the way early. This is not magnolia country so they will require extra care and attention here. I hate to sound like a broken record, but it is either water or soil improvement or both.
            Is it planted in rock? That’s a mistake if they are. These are not desert plants so they will not like rock. The soil around them should be covered with a 4-inch layer of woodchips instead.
Find the perfect spot, like planted in a lawn, and they may flourish for a few years. But don't plant them in a desert landscape.

How many emitters do they have? They will need at least four if they are four or five feet tall. These will be placed in a square pattern about 18 inches from the trunk. This will be enough until they get about 10 feet tall and then you will probably have to bump it up to about six or eight emitters spaced evenly under the tree canopy.
            Making sure these trees get more water will stimulate more leaf development and a denser canopy. The water should be on long enough for it to drain to about 18-24 inches deep after each watering. Use a steel rod like a 3-foot long rebar to judge the depth of irrigation.

Asparagus Planting Among Trees

Q. I put in a lot of effort into planting asparagus. I have a large planted area but no asparagus! I planted Mary Washington this year and many times in the past, but I have had no luck. Are the trees nearby this area competing with them too much?   
Asparagus trials in 2008. About 15 varieties of asparagus were trialed in the Mojave Desert and evaluated by chefs for quality. All 15 performed well but those bred for the hot desert could be harvested for a longer period of time.

A. There is a lot to cover regarding asparagus growing here. First, there is no problem planting asparagus among trees if there is room. I will post a primer on growing asparagus in the Mojave Desert in here.

Make Sure There is Room for It

Asparagus gets 5 feet tall after harvesting the spears so make sure it has room to grow to that height. I have had asparagus planted among fruit trees, as well as alone in rows, since 1996. I planted asparagus in 2019 and they are coming up nicely. This is a great climate for asparagus if it’s planted and managed correctly.
Sometimes you will see advice to "snap" the spears off instead of cutting them. I tired it and don't like it. The remaining stubs above ground interferes with operations. I prefer to cut them about one inch below ground with a sharp knife or asparagus knife.

Just make sure the asparagus gets at least 8 hours of sunlight.

Variety Trials

            I have grown about 15 varieties of asparagus for comparison purposes in our Mojave Desert climate. They have all done well but there are some differences among the varieties. Stay away from heirloom varieties such as Mary Washington because they don’t produce enough spears in any climate. There is nothing remarkable about them.
I trialed a purple variety called Purple Passion years back and liked it. The spears were sweeter but the variety didnt produce as many spears as UC157. Choose improved varieties over the old standbys like Mary Washington. I prefer the UC varieties over Rutgers Jersey line.

            Expect an asparagus bed to last about 20 – 25 years if managed correctly. They do well with drip irrigation. I would use drip tubing with emitters spaced about 12 inches apart or plant them in containers for small spaces. In rows using drip tubing, plant in a triangular pattern so that crowns are 12 to 18 inches apart on either side.
Asparagus grows well with drip irrigation. Make sure you find a balance between soil moisture and drainage. If the soil is too wet, the roots will rot. If the soil is too dry, they don't produce well.

Asparagus Loves Manure or Compost Applications

            Asparagus loves rich soil and water but they also like their roots and crowns to “breathe”. Mix with desert soil an equal volume of rich compost at the time of planting about 12 inches deep. Buy two or three-year-old, all-male crowns and plant them 8 to 10 inches deep. Make sure the soil in the asparagus bed is free of any rocks or they will produce crooked spears.
Asparagus spear emergence in early spring after a rich compost application.

Asparagus Must Have Water Drainage

            The soil must drain water easily in a few hours after an irrigation. Irrigate thoroughly after planting but don’t irrigate again until the soil is slightly moist at 6 inches deep. If you’re not sure about when and how much to irrigate, follow my blog, Xtremehorticulture of the Desert, my YouTube video or podcast on how to irrigate. If watered too often, asparagus roots and crowns will suffocate and rot.

Differences in Varieties

            Plant ‘UC 157’ developed by the University of California for the hot desert and plant them from mid-January to early February. Stay away from planting by seed unless you are an experienced gardener. If you want some variation in spear colors, mix in a variety called ‘Purple Passion’ but keep in mind they don’t produce as many spears as UC 157, but they are sweeter to the taste.
Abnormalities do occur like fasciation but they are rare.

Don't Forget to Fertilize

            Each year, before the beginning of the growing season just after the Christmas holidays, apply about 1 inch of rich compost on top of the soil above the crowns and water it in. If the soil has plenty of organics in it already, then use a mineral fertilizer such as 16 – 16 – 16 in early spring.