If cultivation should be passed over for a few years, the feeding roots become carrier roots, with the feeders chiefly at their ends. Consequently, resumption of deep cultivation after such an intermission may destroy not only the feeding roots but the main roots as well, causing injuries to the plant. If such interrupted cultivation must be resumed, the gardener must be careful not to prune the main roots too severely and should compensate for their removal by pruning the top of the plant at the same time.
All woody plants require large quantities of water, but the conditions under which they may drink are many and varied. Some grow while standing in water; others are killed by water standing about their roots for a few days.
Soil well stocked with organic matter holds more water in a noninjurious manner and yields more of it to plant use than soils poor in organic matter. In some soils the water table is higher than in others. For example, an impervious clay subsoil keeps the water table high, while a gravelly sandy subsoil may let the water drain too deeply to be of any use to the plants. Too high a water table, promoting surface growth of roots, may be corrected by artificial drainage, while compensation for too great a depth may be achieved by applying organic matter abundantly to the soil or by use of plants native to dry regions.
The really conscientious gardener can test the correct amount of water he must supply artificially by digging up the earth about 12 hours after he has watered it and noting how deep the water has penetrated. He must continue these investigations until he has determined how much water to give the plants in each location, for soil varies, as do the depths of the feeding roots.
Here is a good rule to follow in watering:
apply the water at a rate of a small amount per minute and keep it up
for several hours. Put the water on slowly, so that it does not run off.
For shrubs and trees whose branches rest on the ground, water must seep
in to a depth of 5 or 6 inches at least. For trees with upright trunks,
it must reach down to the feeding roots. Whenever practicable, mulch with
earth or litter to prevent evaporation.
Do not water so lightly that only a couple of inches of the soil is soaked. This promotes surface growth of roots, which may be killed by a few days of unusual drying. Water less frequently but more abundantly to achieve penetration of the roots to a depth at which moisture is more consistent.
Use of sprinkler devices
Since no one is likely to have the time to stand on a lawn for several hours at a stretch holding a hose, finely-sprayed lawn sprinklers may be attached to the hose in series to provide protracted waterings at a uniform force without an attendant. Thus, to water a long file of plants, the hose need only be alongside with the sprinklers spaced closely enough to insure that their sprays reach all the plants.
It must be remembered that the greater the number of outlets on a given length of hose, the weaker the pressure of water from each and the closer together they must be placed so as not to miss any of the ground. Watering under shrubs and low-branching trees by such low-pressure devices is better than watering over or through their branches. It is easier to water groups of plants than single ones.
For trees growing on lawns, careful attention is needed, especially when insufficient moisture penetrates the turf, and occasional ground drenchings rather than frequent surface wettings are prescribed.
Here is a simple way to provide subsurface watering for trees: starting halfway between the trunk and the branch ends and continuing that far beyond the spread of the branches, jam holes in the ground to a depth of 1 or 2 feet with a pole or crowbar, spacing them 5 feet apart in heavy soils, farther apart in lighter soils. Run water into the holes slowly to let it spread to the subsoil in beneficial quantities. Close the holes as soon as the ground has dried sufficiently, and make new ones for subsequent waterings.
A good method of watering trees is to attach an 8-inch piece of pipe to the end of the hose, stick it in the ground, and work it down to about 15 inches, using the pressure of the water to help shove the pipe into the earth. Then cut down the pressure and let the water run into the hole, providing subsurface watering.