Trees are a wonderful addition to the landscape, but as with all things in the landscape, proper irrigation is a must, especially for newly planted trees. Oklahomans are no strangers to times of drought, and even established trees will require supplemental irrigation.
While a drip irrigation system is surely the most efficient means of irrigating, there are several methods used to keep new transplants watered when irrigation systems are not installed. Many of these methods also can be used for established trees. The main objective in tree irrigation is to water deeply, so the soil horizon is moist to a depth of up to 12 inches. This is achieved through slow application of water to the root zone.
The simplest way to irrigate is to place the end of the hose next to the tree and allow a slow trickle to run long enough to moisten the root-ball. This is called the open hose method. The open hose method works well for multiple trees as long as you can remember to move the hose after each tree has been adequately watered. Unfortunately hoses are often forgotten and the tree is overwatered and water is wasted through run-off. You can solve this problem by using timers attached at the spigot that will turn off the water after a set amount of time.
Soaker hoses can be circled around a tree to distribute water more evenly throughout the root zone. Soaker hoses are relatively inexpensive and readily available, but it can be difficult to determine how much water is being applied. Soaker hoses don’t typically distribute water evenly along the length of the hose, but in an application such as this, that is not a great concern.
You can use drip irrigation without installing a complete drip irrigation system. A simple and inexpensive way to make your own drip irrigation unit is by using milk jugs or five gallon buckets. Drill holes no bigger than 1/4 inch in the bottom of the containers to allow the water to slowly trickle out soaking the area. A newly planted tree of 2-inch caliper will require about two to three gallons every four to five days, depending on the species. Be sure to refill the buckets every two to three days to keep the soil around the root ball moist.
Larger, established trees are generally more drought tolerant. However, when water is as limited as it has been in Oklahoma the past few seasons, even a well-established tree will require supplemental irrigation. An established tree has a massive root system, typically extending four to five times the width of the tree canopy. Remember, you want to irrigate the soil to a great depth to make the water available to tree roots. Basic lawn irrigation isn’t enough to replenish the soil for trees. Here again, soaker hoses can be a good solution, allowing you to slowly irrigate a large area around the tree.
If using overhead sprinklers, reduce the flow rate and allow sprinklers to run long enough to penetrate the soil horizon.
Remember trees are a significant investment in the landscape and certainly are worth the time and money necessary to protect their continued health.
Kimberly Toscano is assistant extension specialist and host of the OETA television program Oklahoma Gardening, which airs at 11 a.m. Saturdays and 3:30 p.m. Sundays, and assistant director of The Botanic Garden at Oklahoma State University.