Published March 26, 2012 By STEVE HOUSER
Knowing how to work within water restrictions and minimizing their impact to your trees requires more than a simple formula or explanation. Given the variance in soil types and the various types of plants as well as designs in our landscapes, providing for proper watering and maintenance can require advice from the professionals or research on your own. A little of both is ideal.
With or without water restrictions, the basic idea is to water deeply and thoroughly, saturating the soil, almost to the point of running off. Then, let the soil dry before watering again. The top couple of inches should be dry to the touch. If you have clay soil, let it begin to crack at the surface before you water again. If you’re in doubt, dig into the top inch of soil and check it out. Don’t water if rain is in the immediate weather forecast. Allowing the soil to dry near the surface encourages tree roots to grow deeper, adding to the tree’s drought tolerance. Deep root systems also reduce the tree’s likelihood to lean or fall over.
When conditions require severe watering restrictions, the objective of watering is to keep plants alive—not to promote healthy growth rates. Larger native and adapted trees do not need irrigation unless rainfall is below normal. As an example, mature Post Oaks, (Quercus stella) may only need supplemental water a few times during the summer months while drought conditions exist, and not at all during normal conditions. However, Gingko (Gingko biloba) may need irrigation several times a month during drought conditions.
Ginkgo (Ginkgo biloba). Photo by Steve Houser.
The frequency of watering for any species of plant can also vary according to the cultural conditions on a given site. Sites with a clay based soil may hold water better than sand based soils. Once normal rainfall returns, there is no need to water larger native or adapted trees unless health is a problem.
In fact, mature trees are often overwatered when moisture-loving plants are planted under their canopies. Trees prefer compatible companion plants. For our native trees, that means shade tolerant, low water use plants such as American Beautyberry, Mexican Buckeye, Red Buckeye, Turk’s Cap, Plumbago, Blue Mistflower, Lantana, Salvia Greggii, Mexican Petunia, and Coneflower—all of which are quite attractive.
Beautyberry. Photo by Neil Sperry.
Trees also prefer a one to two inch bed of native mulch under the limbs to hold rainfall, conserve soil moisture, reduce evaporation, and lower the soil temperature. However, do not apply mulch near or on the trunk and larger roots.
Watering with automatic irrigation system
The best way to ensure proper watering of your landscape, as well as adhering to water restrictions with an automatic irrigation system, is to rely on professionals. A licensed irrigator can audit your system to reduce waste and offer advice on system updates that can save water. An audit will help you update the system and provide uniform water distribution using the most efficient methods. Next, meet with a professional landscaper and an arborist to determine the frequency and duration of watering based on the plant’s needs as well as the parameters of the water restrictions. The frequency will need to be adjusted according to rainfall events and changes in water restrictions, which does require diligence on the part of the homeowner.
Watering by hand and manual sprinklers
Hand watering typically puts the right amount of water where it is needed but requires your time. Soak the soil completely from the base of the tree out to the ends of the foliage (or drip line). A water hose can be left at a slow drip and moved around. Just don`t forget about moving it or your manual sprinkler. Flooding a neighbor’s yard may not be taken kindly.
Watering with soaker hoses or drip irrigation
Soaker hoses and drip irrigation are very efficient at saving water. Soaker hoses typically have a short life. During a severe drought, neither method is perfect at dispersing the water evenly in the soil. Soil moisture is lacking at deeper levels in the soil and soaker hoses or drip irrigation may not move water outward in the soil as it would in normal conditions. For this reason, avoid adding mulch over the top of a soaker hose laying on the bare soil or over a drip irrigation head on the soil. Placing the soaker hose or drip irrigation head at one-half the depth of the mulch (from the soil to the top of the mulch) encourages more even water dispersal as well as conservation.
Watering recently planted trees
Without rainfall, most newly planted trees require watering two times a week during the late spring and summer months. Watering frequency should be curtailed as rainfall totals increase and fall approaches.