By Marilyn Christensen, Colorado Master GardenerSM, and Carl Wilson, Horticulturist, Colorado State University Cooperative Extension, Denver County
The restrictions on lawn watering and other outside water use in many communities in the Front Range this fall add a new twist to garden chores this season. Because water affects almost every garden practice, consider fall cleanup in a new light and check on specific landscape watering restrictions from your water provider.
There have always been two schools of thought on when to cut back perennial flowers. One school likes to cut back perennial foliage in the fall after it has been killed by a freeze. The second school has counseled delaying pruning until spring to let the dead foliage form its own mulch for the winter.
If you have watered perennials sparingly until now and are unwilling or unable to water perennials this fall and winter given your particular situation, the "let them stand" approach is the one for you. Self-mulching will conserve moisture, as will not opening stems with pruning cuts. As an added benefit, a garden filled with plants provides food and shelter for birds. You can cut back the dead foliage when you do the spring clean up.
If you do choose to cut back perennials, applying a thick winter mulch will be useful. Wait until the plants are completely dormant and the ground is frozen. A 4 to 6-inch layer of mulch will protect perennials from the winter freeze-thaw cycle that opens cracks in the soil and can expose roots to drying. Evergreen boughs placed over perennials provide added protection. Alternate boughs to lock them together to keep from blowing away.
Make compost to enrich soils
The advantage of enriching soils with compost to retain moisture became quite evident during this summer of drought. Fill your compost bins with fallen leaves, grass clippings, and other vegetable and perennial plants cleaned out of the garden. Be sure to hand water the leaf mix this fall to keep the compost process going. Although the compost will not be finished until spring, the value of adding compost to the soil around growing plants when water is scarce cannot be overemphasized.
Hand water trees and shrubs
Providing adequate moisture for trees and shrubs is important for plant health this fall and winter. Excessive soil drying can cause some roots to die; the following year this causes winter-killed branches and twigs to appear on trees and shrubs. Moisture loss from evergreen tree needles exposed to drying winter winds is another reason to monitor soil moisture.
Hand water trees and shrubs one to two times per month when there is no snow cover and depending on precipitation. Water under the branches within the dripline of the tree. Apply ten gallons of water for each inch of trunk diameter. Measure the tree's trunk at about knee height. Water when temperatures are above 40 degrees during the day and never after sunset or when the ground is frozen. Provide a 4-inch blanket of mulch for trees and shrubs, leaving a six-inch space between the mulch and tree trunk. For more information, see Information on Fall/Winter Watering of Trees & Shrubs.
Hand watering trees and shrubs this fall will likely cause lawns to continue to grow underneath. Spot mowing under trees will be needed even though water restrictions that ban lawn watering will cause grass growth to slow in the rest of the yard.
If you haven't fertilized your lawn yet this fall, go ahead and do so. Where restrictions prevent you from watering, you will see benefits next spring instead of this fall, unless timely fall precipitation moves the fertilizer into the soil for you.
As in any year, apply a tree wrap to young and thin-barked trees. This prevents sunscald damage to the bark on the southwest sides of trees when the winter sun is low on the horizon. Apply tree wrap in November and remove it in March.
When planting bulbs this fall, keep in mind the necessity for hand watering. Bulbs require a moist, cool period to start root growth during the winter before they send up blooms next spring. This will avoid "bud blast," or dry buds that produce no flowers, next spring.
Drip irrigation care
The fall water restrictions in many Front Range cities allow the use of drip irrigation systems in addition to hand watering. When the weather turns cold and temperatures are just above freezing, drain the water from main lines and feeder tubing. If ice does freeze in the lines, it will stress the plastic tubing and can pop the emitters off the lines. To drain, locate the lowest point in the system, open the end cap, and let the water run out.
With extra attention to winter watering and mulching, your landscape plants should emerge from winter healthy and beautiful next spring.
Photo: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010