There’s no question that last week’s taste of summer, with inland temperatures reaching the 80s, left many gardeners and their plants gasping for water. A common question once warm temperatures arrive and rainfall decreases is: How long do you keep the sprinklers running to keep plants from drying out?

The amount of supplemental water needed by landscape plants during the summer months depends on a lot of things. Here are some important facts to remember before you turn on the sprinklers.

? Most plants in most areas of Western Washington need water in the summer.

? Frequent, shallow watering leads to shallow roots. Shallow roots lead to more rapid stress under drought or hot conditions.

? Outside watering can be done anytime of the day. It is more efficient however to water at night because evaporation is less.

? Too much water is as bad or worse than too little. The rate of water application should be no more rapid that the rate at which the soil can absorb it.

? Fertilizer spread around plants (including lawns) does absolutely no good at all unless it is dissolved in water. Therefore, fertilizers have to be watered in, and soils have to be moist to get the full effect of the fertilizer application.

During July and August, correct watering is especially important. Daily sprinkling or “hosing down” is the poorest method. Deep watering is required so that the entire soil profile in which roots are growing is moist. The amount of water required will vary with the number and size of plants as well as the soil type. It takes about 1/2 inch of water on the surface to penetrate to a depth of one foot in dry sand. It takes 1-1/2 inches of water on the surface to penetrate a one foot depth in loamy soil, and 2-1/2 inches to penetrate to a one foot depth in clay soil.

The best procedure is to water only when needed as the soil becomes dry. Daily sprinkling is not the method of solving a plant’s moisture needs. The best method is to run the sprinkler for a number of intervals in one 24-hour day. Soak the area deeply, and then do not re-water until necessary. Intervals may be only two days in hot weather if the soil is sandy. A heavier clay soil on the other hand, should easily carry four or five days between waterings.

Water running off the surface is not an indication that the soil is soaked. One possibility is that the type of sprinkler you are using is putting out water too fast. An oscillating arm sprinkler is one of the best ways to apply water slowly. Dedicated gardeners use soaker hoses to do deep watering. For prized plants, placing the hose on the root mass and letting the water trickle for several hours will do a good job of soaking the root zone.

Remember, while water is a critical requirement for plants, air penetration between watering is also necessary. Some mild drying stress is definitely helpful to triggering bud set on flowering plants. Try this with some of your shrubs. Wait an extra day or two before watering and you may be rewarded with more flowers.

One of the best investments home gardeners can make to help retain overall soil moisture is the liberal use of mulches. Mulching materials placed over the soil reduce evaporation from the soil surface, may reduce some water run-off, allow better water penetration into the root mass, and limit weed growth.

Mulches may be organic (shredded leaves, bark, sawdust) or inorganic. Plastic mulches are especially effective in limiting evaporation from the soil surface, but also limit water absorption.

On a final note, remember that anything planted this year and any trees or shrubs planted over the last two years need extra water. Even plants listed as drought tolerant will need extra water if newly planted. Vegetables and fruit plantings need water, especially during fruit development. In addition, plants in containers will need to be watered more often, perhaps twice daily, depending on temperature and wind.