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When irrigating a transplanted tree, it is important to lay out the dripline in a manner that ensures that the plant can thrive in its new environment. To do this, make sure that the soil around the root ball and the native soil are adequately covered with the dripline by installing a minimum of two tree rings. This is accomplished by starting with the first tree ring within 18 inches from the center of the trunk and the second tree ring 36 inches from the center of the trunk.
This may seem logical, but many contractors work with clients who only want to make sure that the tree gets through the first season. This often translates into a single tree ring on top of the root ball or maybe only on the native soil. It doesn’t take long to find out that the customer said one thing to keep the cost down but really expected that the tree would grow and thrive without the necessary number of tree rings.
When a tree with soil surrounding its rootball is planted into a different soil, water will not migrate from one soil to another. It is almost as if a moat exists, blocking the water from its natural tendency to move laterally. As such, both types of soil must be covered with irrigation. This will ensure that the tree’s roots initially receive water on their rootball and the tree’s roots will be adequately watered as the tree matures.
The easiest way to do this is to install rings of dripline around the tree, beginning with a tree ring on the ball itself. How far out should the tree rings continue to be placed from the base of the tree? The correct answer should be to provide all of the tree’s water needs as a full-grown tree.
Root zones often follow the size of the canopy of the tree, so that’s a good start. Work with your cooperative extension or arborist for more information. Once you know the “estimated mature drip edge,” extending the tree rings out is easy, and the tree will not rob water from the surrounding plants or turf.
All of this becomes more challenging when irrigating street trees. Here it is common to place a grate around the trunk along with a bubbler or two, while the rest of the soil is covered with pavers or concrete. But with dripline you can design a layout of tree rings under the pavement surface that will provide water to the roots. Who knows, you may have the first street trees that actually are properly watered and look good, too!
EDITOR’S NOTE: Diane Noecker is director of sales and marketing, landscape division, Netafim USA. She can be reached at email@example.com