COLUMN: GARDENING: Summer care of trees important in desert climate

Summer care of trees important in desert climate

Question: My Chir pine, which has been in the ground and growing well for six years, has suddenly, in the last two months, started dropping its pine needles to the point that the bottom 6 feet of branches are bare. I did fertilize with iron but it did not seem to help. The tree is now about 30 feet high and I sure would not want to lose it. Also, I have a California pepper of the same age that seams to be losing more of its leaves than it is growing. The California Pepper is in a lawn and watered by sprinklers as it has been for seven years. The Pine is in a rock garden watered by bubblers.

Answer: Some of the major reasons for dropping needles are too much water, too little water, internal shading or shade from other trees or buildings, damage to the stems such as mechanical damage or damage from insects and disease. And then there is normal needle drop, but it doesn't normally occur all the way to the end of the branches. I really doubt if it is an insect or disease problem because these types of occurrences are rare on these trees. I am not saying it couldn't be something like that but it is rare and the chances that your tree has them would be less likely.

Since these are on bubblers, I would guess they are getting enough water as long as you are increasing the size of the watering reservoir as the tree gets larger. The size of the reservoir for bubblers needs to be about half the size of the spread of the tree. Reservoirs smaller than this will result in roots trying to penetrate the soil.

The reservoir should be deep enough to hold at least a four inch depth of water after you are finished filling the reservoir. Watering in midsummer will probably be no more than once a week, provided you are watering deeply. Watering more often than this, such as daily or nearly daily, could result in root rotting or crown rot.

Frequent watering can result in trees blowing over because of poor root development and other symptoms such as yellowing, symptoms that resemble drought, needle drop, poor growth and dieback. Trees growing on heavier soils may require watering even less often.

There is another possibility. You mentioned that you applied iron. Chir pines will develop iron chlorosis at times. You will see this from the yellowing of the pine needles usually most severe on the newest growth. Many times, the yellowing will not be even through the entire tree but instead isolated to a few branches at least at first.

In time, it may progress through most of the tree. In cases of progressive iron chlorosis, where it is allowed to progress for several years without treatment, needles will yellow, turn brown on the tips and eventually fall off. When iron is severely deficient, the growth of the branches most affected will have very little new growth. Without new growth for a few years, the needles on the branches will thin out and drop.

Pines must have new growth year after year since this is where the new needles are produced. Small amounts of new growth for a few years results in needles clustered at the ends of branches. If iron chlorosis is a problem, that is yellow patterns developing throughout the tree canopy, treatment can be accomplished by spraying the needles with an iron spray such as iron chelates or even iron sulfate. Most pines respond very well to liquid iron sprays, in fact within 24 hours.

Most foliar sprays containing iron will work. This spray is short-lived and may need to be applied more than once in a year. Do not apply these sprays during the heat or just before a hot day. Or, you can apply an iron chelate inside the irrigation basin to the soil surrounding the tree. The iron to use as a soil application would be an iron product containing EDDHA listed in the ingredients.

These single applications are longer-lived and may last up to three years.

Applying a mulch in the irrigation basin that decomposes easily, such as a composted product, will also help keeping the tree healthy in many ways.

The California pepper is more of a concern. I would be concerned with root problems with this tree. If the tree isn't too big, walk up to the tree and push on the trunk enough to make the tree move. Look at the base of the tree trunk, where it enters the soil, and watch to see if the trunk moves in the soil or if the soil surrounding the trunk moves as you push on it. If it does, this is a sure sign the tree has not rooted properly in the landscape and will be a problem for you as it gets larger.

There is nothing you can do to correct this except remove it since it will just get to be more of a problem as it gets bigger. The problem originated at the production nursery when it was a very small seedling and was never corrected.

Q: I have a silk tree, mimosa, in front yard that is losing its leaves on only half the tree. It has three largest trunks coming out of the ground and only the trunk that faces west is bare. The leaves on the other two trunks are turning yellow but have not started falling off and are still producing the pink fuzzy flowers and seedpods. My tree is planted in the lawn with flowers surrounding its base. It is on the east side and has been in the ground for over 10 years. It is watered by a bubbler for approximately five minutes.

A: Mimosa has some problems with dieback on occasion and there is a disease called Mimosa wilt that causes a limb, or a few limbs, to just die. There is not much you can do about it, but we don't seem to see long-lived silk trees in southern Nevada.

However, planting flowers at the base of trees may cause some serious problems for a tree because flowers need water much more frequently than trees. Trees are deep rooted and so they are best watered deeply and infrequently unless of course they are in a lawn.

Mimosa usually does quite well in lawns just surviving on water that the lawn would get with an occasional (monthly lets say) deep watering.

There are numerous benefits that lawns provide trees and many, like the silk tree, benefit from its association with it rather than planted in a desert landscape with rock mulch. If it were me, I would not plant the flowers at the base of your tree. It can take years for problems to develop in those situations because of the watering of flowers.

The most typical is crown rot or the rotting of the base of the tree at the point where the trunk enters the soil. You can check this by pushing on the tree, provided it is not too large and you can still move it, and see if it is loose in the soil. The tree should be solidly anchored in the lawn and you should see no movement of the soil surrounding the trunk or any space widening around the trunk as it is moved back and forth.

Bob Morris is a horticulture specialist with the University of Nevada Cooperative Extension.


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