When I tell someone how to plant a tree, shrub, rose, or azalea, the instructions are pretty easy until I get to water. The standard questions at that point are:"How much do I water?" and "When do I water?"

The simple answer to these questions are:"Water until wet." and "Water when plants need it." These answers seem obvious, but many people are often confused by such a simple answer. They want some formula to go by. They want me to say "Water every other day with 3.5 quarts of water."

Unfortunately, watering newly planted trees and shrubs can not be reduced to a simple formula. Water needs vary with temperature, wind, sunshine, plant size in relation to root size, soil texture, etc. The list goes on and on.

First let me explain how each variable affects the moisture needs of newly planted trees and shrubs. then I'll give you a test you can use to determine when and how much to water.

Trees and shrubs are usually bought in pots or balled and burlapped. When the root system is placed in a new soil medium, the roots are still configured like the container or the root ball. When you water these newly planted plants, you must water not only the soil around the root wad, but you must also water enough to get the root wad or ball wet.

I have often found that people water the soil around the newly planted shrub, but don't water enough to also get the root wad wet. In effect, the newly planted plant dies from lack of water -- even though the soil around the root wad is wet.

If you are planting shrubs, initially soak the soil until it is mushy. The amount that is needed will depend upon the size of the plant and the texture of the soil. Just remember water until both the root wad or root ball is soggy, and until the surrounding soil is also soggy.

The when to water is determined by the weather conditions. A plant draws water out of the soil through roots. This water moves up the stem of the tree or shrub into the leaves. The water exits the leaves, or transpires, through stomata, or pores in the leaves.

Stomata open up during sunny days. A large tree can lose up to several hundred gallons of water each day due to transpiration. If clouds cover the sky, the stomata tend to close and little water is lost.

Plants lose more water on windy days than on calm days. Water moves from areas of high relative humidity to areas of low relative humidity. On a calm day, water transpires through the stomata on the leaves. Because it is calm the relative humidity of the air near the leaf surface becomes very high. Therefore the relative humidity of the air near the leaf surface becomes the same as the relative humidity inside the stomata and very little transpiration takes place.

On a windy day, the air moves the highly humid air away from the leaf surface and replaces it with air having very little moisture in it. Consequently the relative humidity of the air inside the stomata is much higher than the relative humidity of the air on the leaf surface, and transpiration occurs.

As temperature increases, plants transpire more than at lower temperatures. Temperature affects relative humidity. The higher the temperature, the more moisture it will hold, and consequently, the more transpiration occurs.

As you can see, the frequency of watering will be determined by weather conditions after planting. No formula can be used to calculate plant water needs. Realize that as the sun comes out, as the wind blows, and as the temperature rises, a newly planted plant will need more water.

Quite often I am told that someone didn't water because it rained a day or two ago. Rain quite often is not enough water to give newly planted shrubs. Even after a rain, you may still need to water.

One other thing to remember is that deciduous plants (plants that lose their leaves in winter) need a good initial watering after being planted in the winter. Subsequent watering in the winter may not be needed because they have no leaves through which to transpire. but when the leaves begin to emerge in the spring, watering needs greatly increase.

Evergreen plants planted in the winter continue to transpire all winter long because they don't lose their leaves. Watering in the winter may be required.

As you can see, there are many variables to consider when determining when and how much to water newly planted trees and shrubs. To take the guesswork out of deciding, try the finger test method. Every two or three days, get down on your hands and knees and stick your finger into the soil around the newly planted trees and shrubs. When the soil is wet don't water. When it is dry, get out the hose. When you use this method for the first year or two after planting, you can almost be assured of 100 percent survival for your new plants.