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Saturday, December 26, 2015

Fan Palms Yellowing and Browning

Q. I have three mature California fan palms, aged at least twenty years, planted quite close to each other and located in Mesquite, Nevada. Two or three years ago, one showed signs of early leaf browning and soon died. Now leaves of others are quite yellow but stems and new growth at the top of the tree is green. I'm afraid they are going the same way as the one that died! Disease?
Yellowing palm leaves of the reader
A. I do not think the yellowing and scorching is directly related to disease. I think it is primarily a soil or plant nutrient problem that will not be solved simply by adding fertilizers. Irrigation might be part of the problem IF the trees are watered too often. In your particular case, I think several things may be going on at once.

I’m a big proponent of soil improvement when planting anything in our desert soils. In Mojave Desert soils, and soils brought in as fill around homes in housing developments, soil improvement at the time of planting is an absolute must even if you are planting cactus.
Desert soils are usually very low in organic matter like this soil. The light tan color of the soil is an indicator of a very low percent of organics in the soil.
If your soil is tan colored or very light brown, there is zero organic matter in that soil. Palms are typically planted without much consideration for any kind of soil improvement. They are planted in tiny holes, the roots surrounded with very little if any improved soil. Once planted, the soil surrounding the plant is covered with rock mulch.

In this type of soil environment roots suffocate and die over time. If they don’t die in the first couple of years, they have a great deal of difficulty taking up the proper nutrients from the soil even if fertilizers are applied. They become unhealthy.

The plants react to this poor soil environment by turning yellow. It’s not a disease caused by disease organisms directly but the plant color indicates they are in poor health.

To correct this problem, add organic material to the soil surrounding the roots and improve water drainage and movement of air into the soil. Until this is done, you will see very little improvement to these plants just by adding fertilizer.

In the past we used a technique called “vertical mulching”. It is no longer talked about much anymore but it was effective. Vertical mulching created vertical holes to a depth of 2 to 3 feet around the plant in the root area. These vertical holes were filled with improved soil.

Vertical holes were created using a high-pressure watering device or a post hole digger. Pull back the rock mulch where you are going to create vertical holes a foot or two from the trunk. Create the holes using a post hole digger or water from a high-pressure nozzle to a depth of 2 to 3 feet. Be careful of irrigation lines.

Fill these holes with a 50-50 mixture of the soil you took out of the hole mixed with compost, minus any rocks larger than a golf ball. Create a minimum of four holes around these trees. Use these spots in the future to add fertilizer once a year. Apply more compost on the surface to further improve soil at the surface and put back the rock mulch.

Make sure plastic is not on the soil surface surrounding the plants and under any mulch. Plastic on the soil surface can create similar problems.

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