Drought stress occurs when plant roots are not absorbing enough water for their needs. There are many causes for drought stress. The obvious one is insufficient moisture. However, sufficient moisture may be present but plant roots are not functioning properly to absorb it. There may be just enough present for the plant to maintain itself, but no extra available for growth. In some cases, plants that are over-watered suffer drought stress symptoms. Over-watering drives oxygen out of the soil, which is needed by plant roots for proper functioning. If there is insufficient oxygen, roots die, just as they do when there is insufficient water.
Drought may be of two kinds: short-term and long-term. An example of a short-term drought is the length of a growing season. A long-term drought lasts more than one growing season. While a short-term can damage plants, the long-term droughts are more harmful due to the chronic moisture stress.
Symptoms are the plant’s reaction to stress and provide clues during diagnosis. Following are some common symptoms of drought stress. Be aware, however, that symptoms may mimic. Many of these symptoms may also be the result of other causes such as compacted soil, mechanical root injury, freezes, improper pesticide use and overwatering. Consider weather events and cultural practices along with the symptoms when making a diagnosis.
Deep watering to a depth of 12” inches below the soil surface is recommended.
Saturate the soil around the tree within the “dripline” (the outer edges of the tree’s branches) to disperse water down toward the roots.
For evergreens, water 3’-5’ beyond the dripline on all sides of the tree.
The objective is to water slowly, dispersing the flow of water to get the water deep down to the trees roots. Wateringfor short periods of time only encourages shallow rooting which can lead to more drought damage.
Don’t dig holes in the ground in an effort to water deeply. This dries out roots even more. A soil needle/deep root feeder attached to a hose is acceptable to insert into the ground if your soil is not too hard and compact.
Overhead spraying of tree leaves is inefficient and should be avoided during drought conditions. Watering at ground level to avoid throwing water in the air is more efficient.
During the drought, trees must be given top watering priority over your lawn. However, caring for trees requires different watering methods than your lawn. During water restrictions, irrigation systems designed to water turf do not sufficiently water your trees. During the drought, trees should be given a higher priority than lawns. Lawns can be replaced in a matter of months whereas a 20 year old tree will take 20 years to replace.
How much water your tree should receive depends upon the tree size. A general rule of thumb is to use approximately 10 gallons of water per inch of trunk diameter for each watering. Measure trunk diameter at knee height. General formula: Tree Diameter x 5 minutes = Total Watering Time.
Example: When you hand water using a hose at medium pressure, it will take approximately 5 minutes to produce 10 gallons of water. If you have a 4” diameter tree, it should receive 40 gallons of water - multiply by 5 minutes to equal total watering time of 20 minutes.
All size trees should be watered April through September according to the guidelines below. All trees should also receive adequate water during the winter months too –For more information on winter watering, see below.
Water should be distributed evenly under the dripline of the tree.
The best watering method depends upon whether you have a small (1-7” diameter), medium (8-15” diameter) or large sized (16”+ diameter) tree.
Small Trees (1-7” diameter)–3 times per month, April through September.
Newly planted and smaller trees can get adequate water within the existing watering restrictions by hand watering with a soft spray hose attachment as a separate zone on your designated day.
¨ Small trees are best watered using the following methods:
Automated drip irrigation system/soaker hose.
End of the hose using a soft spray attachment at medium pressure
5-gallon bucket (with ¼” holes drilled in bottom) or watering bags – filled and set under the dripline.
Soil needle (deep root feeder) - Work the needle into the soil at an angle to a depth of 8 inches. Use the needle at low to moderate water pressure. Water the area under the branches in at least twelve sites. Scatter the sites around the area bordered by the drip line. For new trees and those planted within five years, place the needle at least three feet from the trunk. Water a minimum of four sites around young trees.