Keep young trees watered and alive during summer


One of the good things about our area during summer is that our tight clays hold moisture well between rainy periods. That means that a tree or shrub that has been in the ground for a few years will likely be able to cope with nearly any summer drought. This is especially true if the area out to the drip line and beyond is insulated either with a high-quality, biologically active type of native mulch or with several inches of rotting leaves.

But younger trees are a very different story. They have a much smaller root system that frequently dries out during our springs and summers. When this happens, the tree often turns a branch brown, then next loses all its leaves, then dies. Gardeners who planted a much-coveted fruit tree in winter suddenly become aware that it is dead in summer. Trees that have made it through one summer are usually much hardier, but they too sometimes succumb, so you need to be proactive with all young trees.

Over the last three decades, I have killed my share of young trees, and nearly killed many more because I forgot to water. What I have found is that even when it has been raining, we need to check plants for soil moisture twice a week. Checking several trees twice a week can be hot and boring, and maybe difficult to do if you are out of town on vacation, or working long hours, or have a lot of trees to test, but it is essential.

Here's what I do.

In winter, remove plants and turf around newly planted trees and put 3 inches of native mulch at least 2 inches from the trunk. Put mulch at least 2 feet out from trunk. Make a list of all trees less than two winters old. Either put it on a computer or make copies of the list.

Once temperatures get above 70, start monitoring for soil moisture. Unless there have been rains in excess of 5 inches locally that week, you need to monitor. Once a week, make a round of each tree checking for soil moisture. If any are dry, start checking twice a week.

There are generally two ways to do this.

Low tech: early in the day, before the sun hits the mulch, stick your finger through the mulch and feel for moisture. If the soil underneath the mulch is damp, you don't need to water; if it is dry, you do. Generally, if it is damp, you should be able to stick your finger in the clay a half-inch or more.

High tech: The high tech way requires a moisture probe. I bought one 20 years ago at a local nursery for less than $10, and it still works well. The probe has a metal spike you stick into the earth and a meter that reads from dry to wet. The advantage of such moisture probes is that appearances are often deceiving.

After a long dry spell, our clay may be dry six inches down. A 1-inch rain may wet the top inch, and make the soil look wet, when in reality, the root ball down below is still dry.
As well, after very heavy rains, the soil can be mucky, but very high summer temperatures can dry out the top inch. So the soil looks like it needs water when it is actually only needed in the top inch.

Unless you use a probe that can go 4 inches or more down, you are in danger of drowning the plant, wasting water and wasting money; or you are also in danger of not watering and losing the plant you worked so hard to get and plant.

Moisture probes are often available in nurseries. They are essential if you didn't get around to mulching. Also find them online at http://www.e3living.com/node/472 and here.
 
This article is provided by Urban Harvest, Inc. To learn about gardening classes, farmers markets, community gardens and more go to www.urbanharvest.org or call 713-880-5540 for more information. The article was written by Bob Randall, Ph.D., former executive director and co-founder of Urban Harvest. He is also the author of “Year Round Vegetables, Fruits and Flowers for Metro-Houston”.