May through October your plants are actively growing and depend on water to carry out their daily metabolic processes. At times we do not have optimum rainfall during these months. Soaker hoses in foundation plantings once every two weeks for four to six hours will promote excellent health. Sprinklers for trees are a necessity. It is important to remember that woody plants like to have their soils deeply soaked and then allowed to dry before watering again. Constant soaking of the soils deprives the roots of needed oxygen, if roots are drowned the plant performs very poorly and often dies as the result.
WATERING ESTABLISHED TREES
Established trees have roots concentrated in the upper 2 feet of soil and well beyond their branch tips (drip line). Deep watering once every 2 weeks during hot, dry weather will reduce drought stress. The oscillating sprinkler is the most effective in the amount of water it puts out as well as the area it is required to cover. Use only enough pressure to cover the required area (out to drip line). The first signs of water stress in large shade trees is a flagging, or wilting, of foliage. Over-watering can be just as bad as under-watering. Do not water if there has been adequate rainfall. Let the soil get somewhat dry between watering to avoid “drowning” your trees. Apply 2 to 4 inches of mulch around trees. This conserves soil moisture and keeps soil temperature cool. Do not allow mulch to touch tree trunks, keep mulch back about 6 inches. A common mistake is the mixing of plants that have different water requirements. Annuals in large quantities under the canopy of trees can create problems due to the amount of watering they require. Many trees die as the result of soil mounded up on their trunks and flowers planted in that soil. The mounded soil retains the moisture from watering and causes a rot in the living vascular tissue beneath the bark.
WATERING NEWLY PLANTED TREES
Keep the soil moist but not soaked, overwatering will cause leaves to turn yellow or fall off. Water trees at least once a week, barring rain, and more frequently during hot weather. When the soil is dry below the surface of the mulch, it is time to water . Use the touch test to help you determine watering needs. Continue until mid-fall tapering off for lower temperatures that require less frequent watering.
IRRIGATION SYSTEMS AND TREES
It is not uncommon to find plants receiving too much water when an irrigation system is employed. It would seem that many clients are anxious to install and set up a system, never to be revisited again. They are looking to program their system at a constant without taking into account nature’s seasonality and variation in rainfall. If a system is not equipped with soil moisture sensors it will require monitoring and adjustments in order to properly irrigate. Different soil types and plant species will have an effect on water needs, once again monitoring is an effective way to determine the water requirements. There are many fungus diseases that can result from constant wetting of the foliage from sprinkler systems, Juniper Blight being one of the most common. In most cases it is a simple matter of changing the sprinkler head or using s drip irrigation system around susceptible plants.
The installation of irrigation systems can also have negative impact on trees. Arborists urge those who make installations to install their lines as far away from the trees as possible. This will reduce or eliminate the cutting of roots and keeps the lines out of the fertilizing zone. Fertilizing probes easily puncture irrigation lines. It is for this reason that we advise clients to obtain a diagram of line locations from their installer.
There is no question that sprinkler systems properly installed and utilized are an asset to growing healthy plants in the landscape.
The touch test is a very simple but effective way to monitor soil moisture. Using a soil probe, shovel, or garden trowel a sample of soil is taken from a depth of eight to ten inches. The soil is held in one hand and the hand is then closed to make a fist. Upon opening the hand if the soil remains in a wet clump there is no need for watering. If the soil crumples, without forming, it is in need of water. Soil that forms but breaks apart readily when dropped is at a good soil moisture. Soil may have to be checked in several places on any given site depending on the different soils, plants and land forms that may be present.