Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
5/5/00
Contacts:
Jeff Iles, Department of Horticulture, (515) 294-0029,
iles@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Watering Landscape Plants
By Jeff Iles
Extension horticulturist
Iowa State University Extension
It's dry. Very dry. And it just might stay that way for a while. Not a good way to start the landscaping season. So what do we do? Well, we could just close up shop and let our yards turn to dust, or we could bust out the hoses and prepare for battle. Really folks, let's be realistic. This drought can't last forever. But until it begins to rain again, our plants are depending on us to keep them alive. Here's how you can help.
First, let's consider the water needs of newly-planted trees and shrubs. These recent additions to the landscape sometimes possess only a small percentage of their original roots and must be closely monitored for signs of drought stress. Remember, trees and shrubs planted this spring are dependent on roots within the root-ball (for balled and burlapped plants) or the root-mass (for container-grown plants) for water uptake and survival. Therefore, the most important place to check water status (water need) is in the root-ball or root-mass, not in the surrounding backfill soil. Until roots grow into the backfill soil, moisture in the root-ball or root-mass can be depleted very quickly. This is why frequently irrigated trees and shrubs will establish more quickly than those receiving infrequent irrigation. However, too much water can kill plants. Proper frequency and amount of water needed will vary according to area rainfall, moisture-holding capacity of the soil and the site's drainage characteristics.
To water the root-ball or root-mass, apply water slowly near the base of the plant, or use a root-watering needle under low pressure. Water applied too rapidly will be lost through run-off. The frequency of watering can be reduced and the area to be watered enlarged as the root system begins to grow into the backfill and surrounding site soil. Watering frequency can be reduced by spreading a 3- to 4-inch layer of organic mulch over the planting site.
During extended periods of drought, even large, established trees and shrubs appreciate a drink from the garden hose. A single, large tree can transpire away more than 100 gallons of water on a typical summer day. Before applying water, inspect the soil moisture to a depth of 12 to 18 inches with a shovel or soil-sampling probe about midway between the trunk of the plant and the edge of its branch spread (dripline). If the soil is dry, apply water with an oscillating sprinkler (preferably when winds are calm) until the soil is wet to a depth of 18 inches.
Apply water to an area at least as wide as the branch spread. Well-established plants often have extensive root systems that extend far beyond the tips of the branches and will benefit from water applied to the soil outside the branch spread.
Root-watering needles are useful tools for irrigating plants on compacted soils where water tends to run off. But needles should not be inserted deeper than 12 to 18 inches since important absorbing roots are most commonly found close to the soil surface. Root-watering needles should be moved frequently for good distribution of water.
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