Quick Facts...
- Water trees, shrubs, lawns, and perennials during prolonged dry fall
and winter periods to prevent root damage that affects the health of
the entire plant.
- Water only when air and soil temperatures are above 40 degrees F with
no snow cover.
- Established large trees have a root spread equal to or greater than
the height of the tree. Apply water to the most critical part of the
root zone within the dripline.
Dry air, low precipitation, little soil moisture, and fluctuating temperatures
are characteristics of fall and winter in many areas of Colorado. There
often can be little or no snow cover to provide soil moisture, particularly
from October through March. Trees, shrubs, perennials and lawns can be
damaged if they do not receive supplemental water.
The result of long, dry periods during fall and winter is injury or death
to parts of plant root systems. Affected plants may appear perfectly normal
and resume growth in the spring using stored food energy. Plants may be
weakened and all or parts may die in late spring or summer when temperatures
rise. Weakened plants also may be subject to insect and disease problems.
Plants Sensitive to Drought Injury
Woody plants with shallow root systems require supplemental watering
during extended dry fall and winter periods. These include European white
and paper birches; Norway, silver, red, Rocky Mountain, and hybrid maples;
lindens, alder, hornbeams, dogwood, willows, and mountain ash. Evergreen
plants that benefit include spruce, fir, arborvitae, yew, Oregon grape-holly,
boxwood, and Manhattan euonymus. Woody plants benefit from mulch to conserve
soil moisture.
Herbaceous perennials and ground covers in exposed sites are more subject
to winter freezing and thawing. This opens cracks in soil that expose
roots to cold and drying. Winter watering combined with mulching can prevent
damage (See fact sheet 7.214, Mulches for Home
Grounds.)
Lawns also are prone to winter damage. Newly established lawns, whether
seed or sod, are especially susceptible to damage. Susceptibility increases
for lawns with south or west exposures.
Watering Guidelines
Water only when air temperatures are above 40 degrees F. Apply water
at mid-day so it will have time to soak in before possible freezing at
night. A solid layer (persisting for more than a month) of ice on lawns
can cause suffocation or result in matting of the grass.
Plants receiving reflected heat from buildings, walls and fences are
more subject to damage. The low angle of winter sun makes this more likely
in south or west exposures. Windy sites result in faster drying of sod
and plants and require additional water. Lawns in warm exposures are prone
to late winter mite damage. Water is the best treatment to prevent turf
injury (see fact sheet 5.505,
Clover and Other Mites of Turfgrass).
Monitor weather conditions and water during extended dry periods without
snow cover—one to two times per month.
Newly Planted vs. Established Plants
Newly planted trees are most susceptible to winter drought injury. Woody trees
generally take one year to establish for each inch of trunk diameter.
For example, a two inch diameter (caliper) tree takes a minimum of two
years to establish under normal conditions.
Trees obtain water best when it is allowed to soak into the soil slowly
to a depth of 12 inches. Methods of watering trees include: sprinklers,
deep-root fork or needle, soaker hose or soft spray wand. Apply water
to many locations under the dripline and beyond if possible. If you use
a deep-root fork or needle, insert no deeper than 8 inches into the soil.
(See fact sheet 7.240, Home Landscape Watering
During Drought.) As a general survival rule, apply 10 gallons
of water for each diameter inch of the tree. For example, a two-inch diameter
tree needs 20 gallons per watering. Use a ruler to measure your tree’s
diameter.
Newly planted shrubs require more water than established shrubs that
have been planted for at least one year. The following recommendations
assume shrubs are mulched to retain moisture. In dry winters, all shrubs
benefit from winter watering from October through March. Apply 5 gallons
two times per month for a newly planted shrub. Small established shrubs
(less than 3 feet tall) should receive 5 gallons monthly. Large established
shrubs (more than 6 feet) require 18 gallons on a monthly basis. Decrease
amounts to account for precipitation. Water within the dripline of the
shrub and around the base.
Herbaceous perennial establishment periods vary. Bare root plants require
longer to establish than container plants. Perennials transplanted late
in the fall will not establish as quickly as plants planted in spring.
Winter watering is advisable with late planted perennials, bare root plants,
and perennials located in windy or southwest exposures.
For more information, see the following Planttalk ColoradoTM script.
1751, Fall and Winter Watering: during drought
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