Regional Gardening Reports :: National Gardening Association

In the Garden:
Lower South
July, 2001
Regional Report

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Persian shield (Strobilanthes dyerianus) is a summer flower that brightens shady areas with purple and silver leaves. It grows well under trees and shrubs.

Watering 101

I learned a valuable lesson about plant roots and watering when I was growing up. We had a tree just outside the kitchen window. That was in the days when gray water was often routed out of the home and onto the soil. This tree received the water from the kitchen sink and as a result was lush and grew rapidly. We moved from that house to another down the street and within a year the tree was dead. It had developed a very shallow root system, totally dependent on our good supply of gray water. When the new owners stopped using gray water on the tree, its large, lush top growth demanded more than the plant's plumbing could deliver.

Root Growth Basics

Unlike popular diagrams in textbooks showing a tree's root system being an underground mirror image of the top of the plant, most tree and shrub roots are fairly shallow and very wide spreading. But roots can adapt. Research has shown that roots grow where there is a dependable supply of water. If you have a hose bib that drips over a period of time, nearby trees and shrubs will likely develop a significant root system in that spot. If your watering schedule is brief and frequent you can expect your turfgrass to develop a shallow, root system dependent on its next drink.

Roots and Summer Heat

Roots are the plant's plumbing system and the more extensive the root system the better. This lesson is especially important with another hot, dry summer season upon us. It pays to build a resilient root system over time by watering plants with a good soaking on an infrequent basis versus watering shallowly on a frequently basis.

Watering Amounts

During the hot summer weather, if it hasn't rained at least an 1-inch in 2 or 3 weeks it's a good idea to give your trees a good, deep soaking. Apply a minimum of 1 inch of water to insure the water reaches deep into the root zone. Apply the water throughout the area beneath and just beyond the canopy to encourage development of an extensive root system.

To gauge how much water you've applied set rain gauges or straight-sided containers such as coffee cans, around the lawn in various places and note how much time it takes for them to collect 1 inch of water. This is also a good way to also test the uniformity of your irrigation system.

Exception to the Rule

One exception to this deep, infrequent watering rule is for new transplants. Newly transplanted trees and shrubs need a good soaking every few days in hot weather to stay healthy and grow fast during their first year when they're getting established. During their first summer season, they have not yet developed the extensive root system which will sustain them in later years.

I like to use the analogy of an old John Wayne movie. He could ride for 5 days through the desert without water and still be able to take on every villain in town when he arrived. But when he was a baby, his momma had to feed him regularly to keep him going. New transplants are the same way. Get them going well for a few months with frequent watering and then slowly wean them off the water hose.

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