As a follow up to the information in Hotline provided by Bob Mulrooney, the following is additional information from the Plant Clinic of the Morris Arboretum of the University of Pennsylvania.
Drought
Too little water can cause wilting, leaf scorch (browned leaf edges), early fruit drop, stem dieback and plant death. It can also make a plant more susceptible to harmful diseases and pests. Plants draw in water from the soil, use it for plant growth, and then water is released from stems and leaves through a process called transpiration. Plants begin to wilt and suffer drought stress when the transpiration rate exceeds water up-take. Drought is most prevalent in the long days of the summer and can also effect evergreens during dry, windy winters. Also, dry breezes contribute significantly to drought stress.
Signs of drought stress
During a drought, especially such a prolonged drought as we are having, plants may exhibit any of the following:
>upward curling or rolling of leaves
>yellowing and browning of leaves, particularly along leaf edges and tips
>interior needle and leaf drop on conifers
>leaf, blossom, and fruit drop
>under-sized leaves
>twig and branch dieback
Tips for helping your trees during the drought
1) Keep moisture in by laying a 2 inch layer of mulch from the base of the tree out to its drip line to reduce evaporation from the root zone. Remember to keep mulch over the ground under the tree, but not touching the tree’s trunk. Also, make sure the soil around your plant is wet before putting mulch on top of it. You want to hold the moisture in with the mulch, but if there’s no water in the soil to begin with you will not achieve anything.
2) Keep the area around the tree’s root zone free of weeds to avoid competition for water.
3) Focus on the hardiest plants that have the best chance of survival during this drought. Plants recently planted (within the last 2-3 years) will suffer the most as they are still getting established to the new environment.
4) It is often said that pruning will reduce a plants water intake; however, for this to be a significant reduction, at least half of a tree’s foliage would have to be removed. During these hot, sunny days, a plant needs all of its foliage to protect it from sunburn. Because pruning is essentially wounding a plant, a severe pruning job could kill a plant at anytime of season or in any weather. Most horticulturists and arborists are recommending that trees and shrubs should not be pruned during this severe drought. Only prune now if a hazard situation needs to be corrected.
Long-term consequences of Drought
>increased susceptibility to attack by insect borers
>increased susceptibility to certain plant diseases
>root death
>decreased winter hardiness
>dieback and death to branches and twigs in the upper canopy
>eventual plant death
Watering
When: water when your soil is so dry that it cannot be formed into a ball, when you see your plants beginning to wilt, or when the needles of conifers turn a dull green to yellow color.
What time: Water in the early morning or evening. Also, be aware of your towns restrictions on the hours in which you are permitted to water.
How much: The amount of water and frequency of which you have to irrigate will depend on the plant. A good rule to follow is to apply 1 gallon of water per square foot of root zone once a week. Vegetable plants with fruit will usually need to be watered more than once a week.
Watch your plants – they will tell you when they need water by wilting. Also, examine your soil – sandy soils will need to be re-watered more often than soils with high levels of clay.
Application: Water plants slowly and watch to see that the water is soaking into the soil not just running off. You want to make sure that the water is reaching the root zone of your plant.
Using soapy water (gray water): water from washing your clothes or dishes can be used around outdoor plants. The recycled water you want to avoid giving to your plants is any water containing chlorine bleaches. Also, avoid splashing the water on the leaves of your plants. The combination of sun, soap and water could cause the leaves to get burned.
View this information at http://www.upenn.edu/paflora/plantclinic/drought.htm