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GARDENING

Watering Too Much or Too Little Can Stress to Kill

May 31, 1997|From Associated Press

In landscape watering, the goal should be to keep plants from stress.

Longtime gardeners constantly practice looking at a plant for signs of stress and what may be causing it. This requires close attention to not only the plants but also to soil and weather conditions.

A few basic practices smooth the problem. Realize that watering requirements change as a plant grows, and there is a need to water accordingly.

It also helps to group plants according to their water requirements. Place together trees, shrubs and flowers that have high or low requirements. This will help keep them from being over- or under-watered. While not always possible, such grouping should be the leading objective.

Soil salts are water soluble, so deep watering is worth a try whenever a plant seems in trouble. A long, slow watering moves the salts below the roots.

Soil-salt damage often appears much like the injury resulting from abnormally low rainfall or drought. Growth is stunted. There can be yellowing leaves, leaf burn, leaf drop, branch dieback.

Be sure, of course, that the symptoms aren't caused by excess water. Determine moisture depth by how easily a long screwdriver or narrow rod goes into the ground. It will be hard to push into dry soil.

While signs of wilting are bad news, they can be caused by too much water or too little.

Established plants can tolerate some wilting and probably won't die from lack of water. They just won't grow very fast or look as good.

New plants and seedlings will need watering before they reach the stress stage. They become established through root growth and a good top-to-root balance. Some species take one to two years or even more. Until you are sure they are established, give them close attention. Don't try to water on a fixed schedule.

With a newly purchased plant, the original advice is usually to water every couple of days after planting. The plant may look happy for months. But if such watering continues, it begins to wilt and drop leaves despite the attention lavished upon it. Actually, it is drowning from lack of soil oxygen. More water could kill it.

It is better to water every other day for the first couple of weeks and then reduce this to once or twice a week.

Light but daily watering will establish shallow root systems subject to quick drying. Since a plant wilts if the roots don't have sufficient moisture, the deeper the roots go the less vulnerable the plant is to fluctuations at the soil surface and sudden drying.

Deep watering is good insurance. This means applying the water slowly so that it soaks in instead of running off.

Conditions vary, of course, but start by assuming that one to two hours of slow soaking will wet the average soil to a depth of 2 feet and six to eight hours will reach 4 to 5 feet. In general, flowers root at least 1 foot deep; established shrubs 3 to 4 feet deep and most mature trees 5 feet or more.

Mulching also helps. Apply organic material to the soil surface to prevent drying, hold down weeds and keep temperatures cooler.

The most convenient and timesaving method of watering a landscape is likely to be an automatic irrigation system, eliminating the need to drag garden hoses to various locations. Many gardeners find the convenience alone is worth the installation cost. But observe the system frequently while it is running to catch problems before they become serious.

Another good point to remember: Roots don't seek water; they follow it. So they seldom will grow into dry soil.

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