GARDENING : Cultivating Awareness of Watering

All new plants need careful watering, and gardeners--to avoid disappointment and costly mistakes--must understand why.

They also need to understand why watering requirements change as the plants grow, making it necessary to monitor growth and water accordingly.

Although most people use a trial-and-error approach, some basic concepts ease the learning curve.

For example, plants are more adequately watered if they are grouped according to their water requirements. Trees, shrubs and flowers that have high or low requirements should be placed together, so they will tend not to be over- or under-watered.

While this is not always possible, it should remain a leading objective.

It also helps to know the signs of water stress: wilted foliage usually is a good indication of too little water. Sometimes leaves become dull or otherwise off-color. Or stress may appear as curling of foliage and then browning.

Experienced gardeners usually pick up such nuances with a glance, but it probably is the most difficult challenge for others.

A good rule to remember: Established plants can tolerate some wilting and probably won’t die from lack of irrigation; they just won’t grow very fast or look as good.

Conversely, new plants 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’re sure, give them close attention. Don’t try to water on a fixed schedule.

And never forget that watering procedures probably top the list of cultural practices harmful to newly planted trees and shrubs.

The original advice from the nursery is usually to water every couple of days after planting. The plant looks happy for several months. But if such watering continues, it begins to wilt and drop leaves despite the water and attention lavished upon it.

Actually, it is drowning--what was good for it those first few weeks is now killing it. Applying more water finishes it off.

A good starting point is to water new plants every other day or so for the first couple of weeks and then reduce this to once or twice a week. The goal is an established plant with a deep, well-developed root system.

Because deep root systems are encouraged by deep watering, apply 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 two feet, and six to eight hours of slow soaking will reach four to five feet.

Such deep watering also flushes soil salts from the root zone, which is particularly good insurance in arid regions.

Agricultural scientists have developed equations for evapotranspiration rates, which factor in air temperatures, soil types and evaporation to calculate the amount of watering needed.

These often are too complicated for the home landscape, however. Which means gardeners should develop the habit of observing growth changes and water accordingly. A soil probe--even a long-handled screwdriver--works well.

It’s also important to understand that as plants grow, their water needs change. This holds true even for most arid-adapted plants.

Following transplanting, plants undergo a period of establishment. They require more frequent watering at this stage to allow for root growth and to achieve a good top-to-root balance.

In most cases the most convenient and time-saving method of watering a landscape is with an automatic irrigation system, eliminating the need to drag garden hoses to various locations. Most gardeners find the convenience is worth the installation cost.

But get in the habit of observing the system frequently while it is on. This will catch existing or potential problems.