For Release July 9, 2002

Watering Your Landscape is Different Than Watering Your Lawn

by Chuck Otte, Geary County Extension Agent

With the hot and dry weather continuing, it is time to start getting serious about watering landscape plants including annual and perennial flower beds. Many homeowners think that if they are watering their lawn on a regular basis then they donít have to worry about all the other plants in their landscape. Nothing could be further from the truth!

Grass has all of its roots in the top of the root zone. Landscape plants, trees and shrubs, have their roots underneath the grass roots. Most homeowners are not putting on enough water with their sprinkler systems to wet more than the top few inches of soil so the lawn water does little good for the landscape plants. While the tree and shrub roots are below the grass, they are not as deep as most people think. Most of the functional tree and shrub roots are in the top 18 to 24 inches of soil. They do not go as deep in the ground as the plant is tall as was often taught.

Annual and perennial flowers may well need to be watered every 4 or 5 days when the weather is hot and dry like this. Annual flowers, in pots or containers, will probably need to be watered daily. If you water with a sprinkler, do so in the morning. If you are watering with an open hose or a soaker hose, which is my preference, you can water almost any time of the day.

Check the plants first thing in the morning. Many plants will show some wilt in the heat of the afternoon. This is a water conservation tactic that many plants use. If the plants look okay, that is un-wilted, first thing in the morning, then they are not experiencing serious stress. But if the soil is fairly dry down an inch or so, it is probably time to water again. If the plants are wilted first thing in the morning, then they are experiencing serious moisture stress and damage has already been done. Water them immediately. As with everything else, slow deep watering is the best.

Not all trees and shrubs are going to react the same to heat and moisture stress. Non- native trees will stress more easily, especially non-native evergreens like blue spruce and pines. Junipers are a native evergreen more adapted to drought stress, but regular watering is a good idea with them as well. Evergreens donít give us any clues that they are dry. Deciduous trees and shrubs will wilt to show that they are moisture deficient, evergreens can not. We often donít see symptoms of evergreen moisture stress until it is too late.

Water evergreens every 3 to 4 weeks in this kind of weather. The best way to water any of the trees or shrubs is with a slow trickle from an open hose. Root waterers often place the moisture too deep, or are used with too much pressure and create air pockets in the soil. Run the hose at a slow trickle about the size of your finger for several hours. Check on it periodically and if the water is running away from the plant, move the hose to an area under the plant that has not yet received water.

Trees and shrubs of any kind that were planted this year, or the last two years, are going to have higher water needs due to a reduced root zone. These may need to be watered weekly or every other week. It is seldom necessary to water these plants daily. Older deciduous trees and shrubs may be able to get through an extended drought without ever being watered. But one or two deep soakings during a droughty summer will keep them from being stressed. This is important because drought stressed plants are more susceptible to insect and disease problems.


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