UNIVERSITY PARK, Pa. -- This winter's light snowfall coupled with last summer's extended drought means home gardeners should learn to identify signs of drought stress, says a landscape plant specialist in Penn State's College of Agricultural Sciences.

"Even over the course of a year, symptoms caused by lack of water may not appear until late in the summer or into the next year," says Jim Sellmer, assistant professor of ornamental horticulture. "If you wait until you see signs that plants are failing, it may too late to do anything about it. Ideally, you should try to control or reduce drought stress as it's happening."

Signs of extended drought stress

If plants have spent more than one season under drought, they can show a marked decline in the crown of the plant. In addition, twigs and small branches can die back. "Large branches can die or break off under strong wind conditions," Sellmer says.

Sellmer says trees under heavy drought stress may grow suckers (straight, weak, fast-growing branches) on the trunk or upper branches. Cankers, either the result of moisture loss or disease, also can form.

"Another key symptom is heavy seed loads in the year following the drought,"

Other symptoms may be delayed more than a year, Sellmer explains.Water loss may cause extensive root damage, yet the current year's foliage may appear unaffected. "Conifers are particularly difficult to diagnose," he says. "By the time they show signs of stress, they're already in dangerously poor health."

How to avoid water stress

--Keep track of rainfall amounts on your property. "An inexpensive rain gauge or even a bucket can help you track moisture levels," Sellmer says.

--Use drip irrigation, which delivers water efficiently with little waste.

--Carefully scout your plants for signs of drought stress. Sellmer suggests including a few plants that show drought stress early. These plants include Doublefile viburnum, azalea, dogwood, forsythia, Japanese maple, redbud, hydrangeas and herbaceous perennials.

--Pay attention to plants near normally wet areas such as streams, lakes and low areas. "If these plantings lose a water source, their root systems are not developed enough to get supplemental water outside their root zone," Sellmer says.

--Create areas in the landscape using drought-tolerant plants to reduce watering needs. "There are many reference books on drought-tolerant plants," Sellmer adds. "Or, seek suggestions from people at the local garden center, a landscape professional or a Penn State Cooperative Extension agent."

--Use generous amounts of mulch (3 to 4 inches deep) to maintain moisture.

--Do not overplant your landscape, Sellmer says. "Try to design your plantings in groups. Using too many plants looks crowded and strains water resources even further."

Watering guidelines

When to water and how much water to apply depends on the size of the plant and soil conditions. "If you've just recently planted a tree or shrub, the larger the plant, the greater the chance of drought stress," Sellmer says. "You'll have to water more often to establish the plant."

Sellmer explains that ball and burlap nursery trees commonly are grown in heavy loam or clay soils. If the plant is put into heavy soil in the landscape, a single, soaking weekly watering should be adequate.

To establish trees, water them with 1 to 2 gallons of water per each inch of trunk diameter (example: a tree with a 3-inch trunk would get 3 to 6 gallons). New trees planted from containers should be watered at least twice a week for the first 8 to 10 weeks after planting. A ball and burlap tree planted in fine soil should get 2 to 4 gallons of water per inch of trunk diameter.

Shrubs and small container trees should receive 3 to 5 gallons of water twice a week. "Watering should be adjusted depending on the amount and frequency of rainfall," Sellmer adds.

Once trees and shrubs are established (after about 10 weeks of growth), watering can be reduced to once a week. With full establishment (after 1 to 3 years), homeowners can water once every three to four weeks, depending on weather conditions and plant varieties. Increase the watering area to cover the growing edges of the root system. Watering should be slow, allowing the water to penetrate at least 8 inches.

"Water in the evening, to get the most benefit from the water, without worry of evaporation and other factors," Sellmer says. "Use a trickle irrigation system on a timer, tree irrigation bags or gallon water jugs with holes poked in the bottom." Homeowners also should check drip irrigation timers regularly to ensure they are working properly.

Some don'ts during drought

"Do not fertilize during drought conditions," Sellmer warns. "It is a waste of fertilizer and puts a water-deprived plant under further stress. Do not prune, either. This opens up the plant, leading to water loss, and makes the plant work harder to close the wound."

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EDITORS: To contact Jim Sellmer, please call 814-863-2250.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax