QUESTION: When it gets hot, we usually try to sprinkle many of the plants in our landscape to cool them off. Our neighbor told us however, that water drops on a hot day act as a magnifying glass and can actually increase the amount of leaf damage. Is this true?
ANSWER: Research conducted at the University of Arizona was not able to document any harmful effects associated with mid-day sprinkling practices. Plants growing in full sun were sprinkled during mid-afternoon for periods of from 1 to 10 minutes. Without exception, applying water to a leaf caused it surface temperature to drop. In general, the higher the initial leaf temperature, the greater the temperature reduction following sprinkling. Sprinkled leaves remained cooler than dry leaves for 15 to 45 minutes. No detectable damage occurred.
Related research conducted at Oregon State University found that maintaining adequate soil moisture at all times around rhododendron plants will prevent sunburned foliage. Sprinkling to cool leaf temperatures was not necessary to prevent sunburn and may cause leaching of fertilizers from the root zone.
QUESTION: We have several Oregon Ash trees in which the older leaves have started to turn yellow. The younger leaves appear healthy. What's causing this?
ANSWER: After all of the hoopla about how much water fell this spring, some people find it hard to believe that we are entering a period of drought stress. As soil moisture becomes less available, some trees and shrubs show their disdain for water deficits by causing the older leaves to turn yellow and fall to the ground. This leaf drop is a self-preservation mechanism used to slow water loss by the tree. Less leaves on the tree means less water used to cool them and keep them functional.
Woody plants, which have been established in the landscape for at least 3 or 4 years, are tougher and can go without water for longer periods of time. Of course the time frame will most certainly depend upon the species of plant, and the extent and depth of their root systems. Therefore, if the plants are young or have been transplanted within the last year, they will need water more often. A small tree, up to a 2.5 inch caliper, will need about five gallons of water every 7 to 10 days to survive. Larger trees, 3 to 4 inch caliper, will need about 10 gallons per tree every 7 to 10 days. Older established trees can be left alone until the margins of the leaves begin to turn brown (i.e. leaf scorch). Two inches of water should be applied to the area beneath the entire crown of the tree. This irrigation will merely help the tree survive another 3 to 4 weeks without rain if necessary. Don't rely on passing scattered thundershowers to do the job properly because it just won't work! With the soils being so dry and parched, a good steady, gentle soaking is necessary to wet the soil down into the soil profile, otherwise the water will just run off.
QUESTION: Our raspberries and blueberries are just loaded with fruit this year. How often do we need to water them?
ANSWER: Fruit quality, size, and quantity all depend on proper irrigation. If water is limited during the initial period after fruit set and up until color development, the fruit will never reach its maximum size potential. Therefore, most water-limited fruit crops end up producing poor quality fruit. Water is critical for fruit crops from the time blooms drop off until harvest. For example, right now raspberries and blueberries are sizing and ripening. Because both these fruit crops are shallow rooted, they may need one inch of water every other day to once a week. The number of days between irrigations will depend upon air temperatures, wind speed, relative humidity, and the fruit load of that plant. The largest, best fruits are those full of water, sugars and ... teeth marks!
Grays Harbor garden tourWashington State University Master Gardeners in Grays Harbor and Pacific Counties will be conducting their eighth annual Garden Tour this Saturday (July 30) from 10 a.m. until 4 p.m. This year's tour will showcase four spectacular gardens in the Wishkah and East Hoquiam area and will also include the Ross Memorial Rose Garden at the Polson Museum in Hoquiam. Tickets for the tour are just $10 and can be purchased at Elma Variety Store, Valu Drug in Montesano, Marshall's Garden and Pet Store in Aberdeen, Gallery Marjuli in Ocean Shores, Harbor Drug in Hoquiam, Everyone's Video in Raymond and the Rose Cottage in Grayland. Bring a friend, plan to attend and capture a wealth of new gardening ideas.
EDITOR'S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail her at: email@example.com. Donald D. Tapio is WSU Area Extension Agent in Grays Harbor County, (360) 482-2934.