Trees need water?

JAMES DENMAN - Victoria County Master Gardener
Thursday, July 13th, 2006

We are now into the summer months and, unless a tropical wave comes in from the gulf, July through September is typically hot, dry weather. Watering your trees is almost a must during these months.

Many of our prize landscape specimens become stressed during a drought and, as a result, die later on. Some folks are predicting the drought is over, and it may be. But, this is a time we should be paying closer attention to the vigor of our plants so we can avoid losses in the future.

Gauging soil moisture

To those who don't monitor rainfall or those who really just aren't sure, there is always the question, "Do I need to water my trees now or can it wait several more days or weeks in hope of a rain? There are all sorts of fancy gadgets for monitoring soil moisture but one of the simplest and cheapest I learned about from Victoria County Extension Agent Joe Janak is an old, long screwdriver.  Now how can a screwdriver do that? Get a screwdriver, preferably 12-18 inches long not counting the handle, and insert it into the ground. No dials to read, no numbers to punch; just simply push it into the ground. If it goes in 12 inches easily there's no need to water. Six inches? Start thinking about it! Three inches? Get the hoses ready! Can't get it in more than an inch? Start watering.

According to the Texas Forest Service, we should water trees after four weeks without any significant rain (1 inch or more). Mature trees should be watered about every 10 to 15 days thereafter. Young trees newly planted or less than 2 years old should be watered about once a week.

One tip that we learned as master gardeners is that most plant roots must have equal amounts of water and air in the soil. So if a soil is watered, it should be followed by a drying time - thus the one- to two-week watering intervals. Otherwise the soil will be saturated with water and have minimal soil oxygen, which causes root loss and tree death.

Symptoms of stress

Some drought stress symptoms are leaf color, leaf rolling and leaf dropping. Observe normal healthy plant leaves. While it varies by species, they are typically a good green color. Drought-stressed leaves are usually a shade or two lighter in color and have a dull, even grayish characteristic. Some tree leaves roll or curl to lessen evaporation as water supplies shorten. Still others drop leaves prematurely. Cottonwoods, sycamores, figs, bur oaks and other large-leafed trees tend to drop leaves when water stressed more so than other tree species. So if you miss probing your soil but see leaves falling, it could be past your time to water.

How to water

The best way to water trees is irrigating through a soaker hose. Individual lengths of soaker hose should never exceed 100 feet. The soaker hose can be "snaked" back and forth about 1 to 3 feet apart starting just outside of the tree's dripline and advancing toward the trunk and then on the other side of the tree. Snaking the hose allows easier removal and avoids going around and around the tree. Check for excessive leaks and allow it to irrigate for two to six hours depending on flow rate but soaking to at least a depth of 12-18 inches. The hoses now come with built-in pressure regulators to help you adjust to the proper water pressure.

Regular open hose watering also can be used on shrubbery, fruit, pecan or shade trees but works best on young trees due to the small wetting pattern and frequency of moving required for large trees. Control the water flowing from the faucet to a very low flowing rate, about the thickness of a pencil or your little finger depending on how quickly it absorbs into the soil and so as to avoid runoff.

Depending on the size of the tree, it may be necessary to reposition your hoses around the plants or trees being watered.

It is wasteful and best to not water near the trunk of any tree. Excessive watering by the trunk can cause large roots to rot when small feeder roots are the ones that you should be watering. The majority of these are away from the trunk extending past the length of the branches. The majority of the water should be applied in the dripline area, moving in toward the trunk and out past the dripline.

If you are using the sprinkler irrigation method to water trees, the best time to irrigate is early morning. This will allow the foliage of plants drying time during the day, which will lessen diseases. Use empty food cans to gauge irrigation, applying 1-2 inches of water that should soak 6-18 inches deep. Once again, use your screwdriver to measure soil-probing resistance and the depth the water has soaked.

For more sophisticated watering plans, there are electrical or battery-powered irrigation systems that operate water valves through timers turning them on and off as needed. This will control your watering needs and usage, yet still allow you a watering plan even when you are gone for extended periods. Most garden centers have these timers.

Old-timers often stick to their own ways. My grandfather in the 1940s and 1950s had an acre of land he used for his vegetable garden. He raised all of his vegetables in sandy soil and never watered or had irrigation. He depended on rain and early morning dew.