Woody Plant Management in a Dry Climate

By James Klett, Michael Bauer, Patrick McCarty, Susan Rose, Curtis Swift, and Greg Vlaming, Colorado State University Cooperative Extension, Horticulture

No Current Watering Restrictions

The following practices will help keep your trees and shrubs healthy while conserving water.

• Check your irrigation system

• Check your system's coverage by placing out shallow containers, like cat food or tuna fish cans, at several locations, and measuring the depth of the water.
• Replace damaged heads.
• Adjust heads to avoid watering streets or driveways.
• Adjust heads to water the feeder root system more directly, without hitting the main trunk(s) of the tree or shrub.
• Water between 9 PM and 9 AM.

• Use sprinklers that apply large droplets of water at a low angle. Fine spray mists and sprinklers that throw water high into the air often waste water from evaporation.
• If you do not have an automatic sprinkler system, use a bubbler at the end of a hose to apply water at a low rate at several locations beyond the drip line. Remember, the roots on established trees extend 3 to 5 times the height of the tree.
• Do not try to save water by installing a drip irrigation system around the base of an established tree; tree death will likely result.
• Water deeply and infrequently; this will increase the plant's drought tolerance.
• Water the entire root zone.
• Root of established trees are 3 to 5 times the height of the tree.
• The roots of shrubs also extend wider than the above-ground plant.

• Select trees and shrubs for the landscape that are tolerant of low water situations.   Instead of planting spruce, plant pines; pines require less water.
  • Trees and shrubs have varying degrees of water requirements
  • When selecting plants for the landscape, place those with the same water needs together and irrigate to their requirement.

Possible Choices

Click on highlighted names for photos and/or information on that plant:

Deciduous Trees

Shrubs

• Water trees and shrubs thoroughly in the fall to ensure they go into the winter in a moist condition.

• All landscape areas should be watered thoroughly in late fall to ensure there is sufficient moisture in the soil to provide their water needs until spring.
• Watering or fertilizing too early in the fall can reduce the plants's ability to acclimate for winter conditions and could result in more winter injury. Do not fertilize with nitrogen after mid-July.

• Water monthly during winters when little snow is present.
• Apply water at a rate that allows maximum infiltration at the rootzone but limits runoff.
• Wrap trunks of newly planted deciduous trees during the winter for the first two years; November through April.
• Do not apply nitrogen fertilizer just prior to the heat of mid-summer; severe stress would result in ore frequent applications of water.
• Apply a 3 to 4 inch layer of mulch a minimum of a two foot area around the trunk. Keep the mulch two inches away from the trunk.
• Use organic mulch such as bark or wood chips. Avoid the use of stone or rock as much near plants as this increases air temperatures and moisture loss from leaves and stems.
• Check moisture in root balls of newly transplanted trees to maintain adequate moisture.

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If Restrictions are Expected in the Next Few Weeks or Mild Restrictions are in Place

• Continue to irrigate, soaking the root system once every 4 to 6 weeks. Don't water every other day just because it is allowed
• Be sure your mulch layer is in place.  Place 3 to 4 inches deep and avoid mulch right against the trunk, as this can harbor insect pests and diseases that may harm the trees.
• Kill turf near trunks of trees and shrubs with a herbicide such as glyphosate (Roundup). After the grass has dried, apply a layer of mulch.  Mulch the area around trees and shrubs out as far as possible with an organic mulch layer. Place fabric material (not polyethylene) under the mulch first if desired.
• Avoid planting new trees or shrubs, even drought tolerant ones, because all new plantings need more water to establish.

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When NO Watering is Allowed

• Restrict traffic over the root zone of established trees and shrubs if possible.
• Extend the mulch layer over as much of the root zone as possible.
• As dieback occurs, prune out deadwood. Avoid cutting into living wood, even if this means leaving temporary stubs.

• Deadwood serves as a source of infection by disease organisms and may attract insect pests which then invade the rest of the tree.  Cutting into live wood increases the chance for tissue dehydration. Leaving a short stub will help prevent dehydration. The stub will need to be removed at a later date when irrigation water is again available.

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After Watering is Again Available

• Begin irrigation, soaking the root system once every 4 to 6 weeks.
• Do not attempt to make up the drought by watering too often. Keeping the soil too wet will cause root rot and other related problems.

• It is a natural tendency to over-water and over-fertilize plants that are observed having problems. This practice will generally only create additional stress.

• Water monthly in dry winters to keep roots healthy.

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Photo: Judy Sedbrook

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Date last revised: 01/05/2010