Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
5/8/00
Contacts:
Richard Jauron, Extension Horticulture, (515) 294-1871,
rjauron@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Yard and Garden column for the Week Beginning May 12
Watering Guide for Home Gardeners
By Richard Jauron
Extension horticulturist
Iowa State University Extension
Most areas in Iowa are currently in the grips of a severe drought. If the dry conditions persist, home gardeners may have to make some difficult decisions. The following questions and answers on watering may help the gardener deal with watering concerns.
How often do I need to water?
A deep watering once a week should be adequate for
fruit, vegetable and flower gardens. Apply 1 to 1.5 inches
of water per week. A weekly application of 1 to 1.5 inches
of water also is adequate for an established lawn. The key
to watering newly planted trees and shrubs is to check the
moisture status of the plant's root-ball or root-mass. The
roots of newly planted trees and shrubs are initially
confined to the plant's root-ball (balled and burlapped
plants) or root-mass (container-grown plants). Since the
root-ball or root-mass can dry out very quickly, its
moisture status should be checked frequently. Newly planted
trees and shrubs should be watered when the root-ball or
root-mass (not the surrounding soil) begins to dry out. To
water the root-ball or root- mass, slowly apply water to the
base of the plant. The frequency of watering can be reduced
and the watering area enlarged as the plant's root system
begins to grow into the backfilled and surrounding soil.
Small trees usually require watering for one to two growing
seasons. It may be necessary to water large trees for three
to four years.
These are general watering recommendations. The frequency and amount of watering is largely determined by soil characteristics and weather conditions. For example, sandy soils require more frequent watering than loam soils. Adjust your watering practices to specific weather and soil conditions.
When should I water?
When irrigating with a sprinkler, early morning (5 to 9
a.m.) is the best time to water. A morning application
allows the water to soak deeply into the soil with little
water lost to evaporation. When watering is completed, the
plant foliage dries quickly. Watering at midday is less
efficient because evaporation is rapid and strong winds may
cause uneven water distribution. Strong midday winds also
may carry water onto driveways, patios or streets, wasting
considerable amounts of water. Watering lawns and gardens
with a sprinkler in the evening or at night may increase
disease problems.
In fruit, vegetable and flower gardens, drip irrigation systems and soaker hoses generally are more efficient and cause fewer disease problems than sprinklers. Mornings and evenings are excellent times to water gardens when using a drip irrigation system or soaker hose.
Are there ways to reduce water use in the garden?
Apply a mulch around landscape plantings and garden
areas to conserve soil moisture. Mulching reduces the rate
of evaporation from the soil surface and also limits weed
competition. Organic materials, such as grass clippings,
straw and shredded leaves, are excellent mulches for the
vegetable garden. Wood chips, shredded bark and ground
corncobs are good choices for trees, shrubs and
perennials.
The depth of the mulch depends on the type of material used and crop. Apply wood chips and shredded bark to a depth of three to four inches around trees and shrubs. Optimum depth in the vegetable garden ranges from two to three inches for fine materials, such as grass clippings, to six to eight inches for straw.
Is it necessary to water established trees and
shrub?
Large, well-established trees and shrubs that are well
adapted to our climate should not require watering at this
time. Well-established plants have extensive root systems
and should be able to absorb sufficient amounts of moisture.
Trees and shrubs that are native to Iowa or similar
climates are adapted to harsh weather conditions.
Trees and shrubs, such as the European mountainash and paper birch, are not well adapted to hot, dry conditions. Extended periods of dry weather are extremely stressful for these plants. The weakened paper birch and mountainash are often attacked by insects and disease pathogens, resulting in their eventual destruction. European mountainash, paper birch and European birch should be watered during dry periods to prevent major problems in the future.
Other trees and shrubs in the landscape that would probably benefit from watering include pagoda dogwood, redbud, beech, tuliptree, rhododendrons and azaleas. If the drought persists, even the large, well-established trees and shrubs would welcome watering by mid to late summer.
Is it necessary to water an established lawn?
Cool-season grasses, such as Kentucky bluegrass, can
survive extended periods of dry weather. The turfgrass
plants stop shoot growth and go dormant. Dormancy is a
natural survival mechanism for turfgrasses. While the
leaves have died and turned brown, the turfgrass roots and
crowns remain alive. Generally, turfgrass can remain
dormant for four to six weeks without significant damage to
the plants.
If I do decide to water my lawn, how and when should
it be watered?
The appearance of the turfgrass is the best way to
determine when to water the lawn. The ideal time to water a
lawn is at the first signs of water stress. Turfgrasses
that have adequate supplies of water are normally dark green
in color. For cool-season grasses, such as bluegrass, the
first signs of stress are a bluish green color and
footprints that remain in the turf after walking across an
area.
Most lawns in Iowa need 1 to 1.5 inches of water per week. When watering the lawn, apply this amount in a single application or possibly two applications three or four days apart. Avoid frequent, light applications of water, which promote shallow rooting and lush growth. Lush, shallow-rooted turfgrass is less drought tolerant. To determine the amount of water applied by the sprinkler, place several straight-sided cans within the spray pattern. Then measure the amount of water collected in the cans with a ruler.
What should I do if I allow the lawn to go dormant,
but the drought persists through the summer?
Dormant lawns are in jeopardy of dying if drought
conditions persist over an extended period. It's best to
water the lawn if the turfgrass has been dormant for four to
six weeks. Apply 1 to 1.5 inches of water in a single
application. This will not cause the grass to green up, but
it will keep the turfgrass crowns and roots alive. If the
dry weather persists, water the dormant lawn approximately
every four weeks.
ml: isugarden
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