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Journal American Rhododendron Society

Current Editor:
Dr. Glen Jamieson ars.editor@gmail.com


Volume 30, Number 3
Summer 1976

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Watering is More Than an Act of Kindness
Arthur W. Frazer, Alexandria, Virginia
Reprinted with permission from Azaleas newsletter.

watering can and hose

        Without doubt, the three most important considerations in growing good azaleas are: 1) good soil; 2) insect control; and 3) adequate moisture. The requisites for good soil have been discussed, and I hope I leave no room for doubt about it being the single most important key to success. It's like digging a proper foundation for your house - or mastering fractions in the third grade. It can be irksome, but once overcome you have the rewarding feeling of having slain the dragon.
        Running a close second in importance - but much easier to tend - is adequate water. Strangely, the neglect to provide adequate water turns out to be the problem many times when I receive an urgent call to "come out to see what's happening to my azaleas". This shows up in several ways - sometimes months after the initial problem. Sound weird? Not at all, because a sick plant expresses its symptoms in different ways - and a plant without water is a sick plant! But we're getting ahead of ourselves.
        A plant is constantly absorbing moisture through its root system - the means by which the soil nutrients are carried into the plant. The water within the plant also serves as a solvent and transmitting agent for the carbohydrates and sugars being manufactured by the leaves. It acts also as a coolant, and in truth is a close comparison to the human blood stream in many respects. But in addition to all these functions, the moisture being taken in by the roots is vita/ to replace the moisture being constantly transpired (evaporated) through the pores in the leaves. On hot sunny days the demand for water is greatly increased to replace that lost by evaporation - just as we need more water to replace that lost through perspiration. Not so generally recognized is the heavy loss of water through transpiration by broadleaf evergreens during winter when the cold winds, low in humidity, virtually suck the water out of the leaves. (Which explains why leaves on rhododendrons, and sometimes on azaleas, in very cold windy weather tend to curl up to reduce exposure to evaporation.) But nature is marvelous and it anticipates this excessive wintertime evaporation of moisture through the leaves by generally providing more ground moisture through winter rains - except when the ground is frozen. More than this, it attempts to add a safety factor by causing the azaleas (and other broadleaf evergreens) to lose part of their leaves, hence less surface to expose to evaporation. Unfortunately, or perhaps fortunately, an unthrifty or sickly azalea, in its struggle to survive the stress of winter, will lose more than its customary portion of leaves and if it survives will enter the following spring with fewer leaves to manufacture the food it normally requires.
        Once more remember the astounding fact that 50 to 60 per cent of the plant tissue of an azalea is water! I presume the same proportion holds for other broadleaf evergreens. Little wonder then that they are all described as moisture loving plants. What happens when there is an inadequate supply of moisture? Several things can happen, some of them obvious and immediate, others less obvious, but just as real.
        First, and certainly the most obvious when moisture is suddenly denied is the wilting and drooping of leaves, frequently followed by heavy leaf drop in mid-summer. Even if the leaf wilt is only mild, and temporary, the plant has suffered major shock. Part of the leaves, the plant's little food factories, have been temporarily, or permanently, put out of business.
        Second, as a secondary effect of the above crisis, or as the result of a less obvious chronic shortage of moisture, the plant becomes sickly (just like a malnourished human) and less resistant to survive the misfortunes and minor calamities which befall all living things. For example, winterkill (bark split) is often the final blow to a sickly plant, rather than a question of basic hardiness or winter severity.
        Third, although failure to produce flowers may be attributable to dense shade (as opposed to "high shade"), the sudden failure to bloom, or sparse blooming in a given year is almost invariably a suspicion that the azalea lacked adequate water during the previous summer. Remember, the buds for this spring's flowers began to be developed during mid-summer last year. In the Washington area this coincides with what is usually the driest season of the year. Azaleas cannot successfully bear the burden of developing flower buds and combat drought at the same time.
        Fourth, a mid-summer drought which stops secondary vegetative growth (and bud production) followed by an early wet fall, frequently encourages an unusual amount of new growth, too late to harden off before winter. The almost inevitable consequence, given a normal winter, is winterkill of all the new branchlets on the plant. (Late fertilizing, after June 1st, will generally create the same problem.)
        Fifth, during winter greater evaporation of moisture through the leaves than the roots can replace will cause ''leaf burn'', i.e., the tips of the leaves - sometimes the entire leaf - literally dehydrate and turn brown. Again, the "food factory" function of the leaves is impaired. The cause is either an unusually dry winter (not common in Washington) or more likely a severe prolonged freeze that has tied up the moisture available to the rootball.
        Why this preoccupation with healthy leaves - and the reason for referring to them as "food factories"? Leaves are vital to the production of the principal plant nutrients. In addition to transpiring moisture through their pores (stomates), leaves take in carbon dioxide and, by the action of light and/or sun on them, turn the carbon dioxide into carbohydrates (sugars and starches). This is the process known as photosynthesis and its vital importance is succinctly described by Dr. Clement Bowers:

"...Like humans, plants get most of their energy and do all their work through sugars, starches, fats and proteins. Their tissues are largely composed of carbohydrates (35-45%), only 5% being made up of the minerals which they obtain from the soil and which you apply as fertilizers. The remainder of the plant is made up of water (50-60%). Carbohydrates and water are, therefore, the main components of a living plant."

        By now I guess I have made clear the perils of cheating when it comes to providing water for your plants. It's like playing Russian roulette. You may luck out a few times, but eventually something is going to end up dead, in this case, azaleas. Forgetfulness and carelessness are just as deadly. Prolonged vacations fall in the same categories.
        During the 8 months of fall, winter, and spring, Washington rainfall is customarily adequate. It's the four summer months beginning in June when we frequently have insufficient rainfall, although April and May have sometimes produced droughts, as in 1971 .
        Avoid needless watering. Azaleas, and most other shrubs, need one inch of water every week, or 10 days. But two inches isn't twice as good. Don't be misled by summer thunder showers, which are often more noise than effect. By no means trust your intuition, wishful thinking, or aching joints that "it's going to rain in the next day or two". This is the kind of poor judgment of which calamities are made.
        By far the best assurance is to buy an inexpensive rain gauge, or cheaper yet, set an empty tin can (as we do) out in the open away from trees and house. When it rains, remember the next time you are outdoors to check the depth of water in your can. Keep the cumulative total in your mind for each rainfall, or if you're forgetful, as I am, mark it on your calendar. That way you have an accurate answer to how much sprinkling, if any, you need to do. We prefer an oscillating sprinkler (back and forth). Set a larger pan (because of the angle of spray) under the sprinkler until you learn how long it takes to put out ½ inch, 1 inch, etc., of water.


Volume 30, Number 3
Summer 1976

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