Watering: Hot Weather Tips to Save Your Plants

For 50 years, the husband and wife team of George “Doc” and Katy Abraham wrote a syndicated gardening column and hosted a call-in radio program in Rochester. Here is a reprise of one of their “Green Thumb” articles from 1988, offering tips for conserving scarce water while protecting different classes of plants from dry spells. The complete archive of Doc and Katy’s life’s work can be found at the Kroch Library at Cornell University.

During dry spells, a shortage of water can be as damaging to plants as insects or diseases. Sometimes water shortages persist for three or four summers or more. When that happens, home gardeners must conserve ground moisture in every way possible.

Soil is a storage place for water, and every drop of water must be carefully used to make sure that the ground moisture isn’t wasted. Consider where our water comes from: All the fresh water in the world adds up to only about 1/30th of the water in the salty oceans. And one-third of that fresh water is locked up in snow and ice. Much of the rest is too far underground or too loaded with minerals to be usable. So all the fresh water needed by man and life on Earth must come from the rest.

Water is supplied by the “water cycle” in which water rises into the sky as vapor and falls back to earth as snow or rain before running downhill to a body of water like a lake or the sea. It then evaporates again into the sky. It is a process that repeats itself endlessly. Nature distributes water very unevenly, so you might get plenty but a neighbor a few miles away might not. The average person in the U.S. uses from 100 to 150 gallons of water a day (residentially), and a family of four uses over 400 gallons without any allowance for use on plants.

The home lawn
First, you should know that it is not necessary to water the lawn in drought times to keep the lawn alive. Lawns go dormant in hot weather and will snap back after a good soaking rain. In some areas, there is a ban on lawn watering. If you happen to have all the water you want and want to go to the trouble of watering, you can try one of two tricks:

1. Water often and lightly, like golf course keepers do, never allowing the soil to get dry, which takes built-in sprinklers, or,

2. Water deeply but not so often (the most practical method).

Average soil under drought conditions loses about 50 gallons of water daily for each 1,000 square feet. That means about three hours of steady sprinkling is needed weekly to replace that amount. To me, a lawn is not worth all that expensive water. A lawn is a beautiful thing to behold but if water is scarce and expensive, it might be more sensible to skip watering it during droughts. If you are going to water, do it in late afternoon instead of during the heat of the day to prevent water loss into the air.

Trees and shrubs
Trees and shrubs are too often the “neglected orphans” around the home. Few people think to water them. Trees absorb great quantities of water from soil and lose it into the air by transpiration. It takes 1,000 pounds of water to make a single pound of dry wood. A tree 35 feet tall will give off about 35 gallons of water a day during mid-summer. A 15-foot oak will transpire about five gallons of water in just one hour.

You can punch holes 18 inches deep and 2 feet apart in the soil around your trees and let water run into the holes. Add liquid plant food to save the life of trees during a critical water shortage. Feeding promotes new root growth and sustains tree vigor over the long haul. Use mulches – wood chips, pine needles, sawdust, sphagnum (peat moss) or cocoa bean hulls – to keep tree roots cool and moist. Dig away the sod at the tree’s base and fill in with mulch.

Evergreens in foundation plantings or alone, can be sprayed with a protective anti-transpirant to reduce transpiration from hot winds of summer. Anti-transpirants with either a plastic or rubber base may be sprayed on leaves or needles of trees.

Another hot weather trick to reduce water loss is to head-back (cut back) tall trees. This is needed to combat the loss of roots that dry out and die from lack of water. Dead roots can breed fungi such as common root and heartwood rots. This plus invigoration (feeding) will keep prized trees and shrubs alive and thriving.

If water use is not restricted, remove the hose nozzle to reduce pressure and allow water to flow over roots until the soil is saturated. You can tell water shortage by leaves that droop and tend to curl along the margins. Water before danger signs appear! Use wash water, laundry water or dishwater – just about anything you can get your hands on will work.

Gray water (previously used) is generally fine, provided you do a little homework. Don’t worry if it contains detergents, soaps, ammonia, etc., but watch out for boron, as it’s toxic to plants. Ammonia even supplies nitrogen. Be aware, however, that many soaps and detergents contain salts that can build up in the soil over time. Avoid using softened water because it, too, can carry excess salts. Use gray water only on mature plants (primarily ornamentals), as seedlings aren’t always vigorous enough to withstand it. Also, if you must use it on a vegetable garden, do not wet the foliage, but apply directly to the soil at the base of the stems. Do not use it on root crops or leafy vegetables such as lettuce. A rule of thumb is one half-gallon per one square foot once a week. Alternating fresh and gray water is recommended, as is fertilizing regularly.

Vegetables and flowers
Most vegetables are about 90 percent water. That means they must have an even supply of moisture, 1 to 2 inches per week. This can be supplied by perforated hose, porous hose, soakers or sprinklers. Overhead sprinklers are not recommended because they tend to increase leafspot and other diseases by splashing spores.

Let the water run down between the rows. Water any time day or night. Time of day is not important, but if you water in the afternoon, you lose some water to the heat of the day. Use water from ponds, streams, wells, rain barrels, cisterns or city water. Don’t worry about chlorine, iron, calcium or magnesium.

Mulching your vegetables is good business. It will control weeds and reduce surface loss of moisture. Use straw, peat, wood chips, sawdust, leaves … anything. Mulches keep roots cool and prevent leaf curl, blossom end rot and cracking of tomatoes and other vegetables. Water your plants thoroughly and apply the mulch to trap moisture in. Also, just because you use a mulch does not mean you won’t need additional moisture. Your plants will grow vigorously under a mulch and will pull a lot of moisture from the soil, so continue to water regularly.

Avoid cultivating your vegetables in dry weather. This loses moisture to air. Unnecessary deep hoeing will also waste precious soil moisture. A packed soil wastes water by runoff, but if your soil has a heavy crust, it can be improved by shallow cultivation. This lets water enter instead of run off. The secret is to save moisture by trapping it in.

Flowers all need ample water but, again, you should not sprinkle these from above. Overhead sprinkling encourages botrytis blight and other flower and foliage diseases. Apply a soaker and let the water run to the base of the plants. No need to wet the foliage or flowers. After the soil has been soaked, add a layer of mulch.

House plants
House plants, indoors and outdoors, need water. Give them a good watering when you do it, and allow the plants to go a bit dry between waterings. It doesn’t harm most plants to get a bit dry. Outdoors it toughens them by hardening the cells, enabling them to withstand drought better. If water is allowed to remain at the roots constantly, it keeps oxygen out and the plants suffocate.

Too much water causes a peculiar odor. Gardeners say that the soil is ‘sour’ when that happens. Actually, a wet soil is no more likely to be sour than a dry one; you’re just more likely to be able to detect the smell from wet soil. The odor is due to gases (mostly methane) produced by micro-organisms working in the absence of oxygen. A fair rule of green thumb: Give plants a good soaking when you do it, then allow them to dry out a bit between waterings. This works fine for all plants.

Miscellaneous notes on watering
Watering while the sun is out will not burn your plants. You can water any time, even during the heat of the day. Shortages of water seem to be more critical during some periods of the life of the plant than others. Generally, at pollination and fruit-setting time, water is more crucial to their survival. Most plants can survive prolonged dry spells if they have ample water during these important periods. Also, plants use more water in July and August than at any other time because the days are longer and temperatures higher. Thus, a 20-day drought in May or October is equal to only 10 days of drought in July or August.

Also, recharging the root zone of plants takes a lot of water. Sandy soils hold about one-half inch of water per foot, and loams with sand hold 1 inch per foot. Loams and clays hold about 2 inches. In other words, a loamy soil can go four times as long without water, but requires four times as much to recharge it as a sandy soil. For example, it will take 350 gallons of water to recharge 1,000 square feet of sandy soil, but 1,400 gallons for 1,000 square feet of a loamy soil.


by Advice from Doc and Katy