and Shrubs in Times of Water Restrictions
for Responsible Planting and Care
- Planting trees and shrubs during times of drought and water
restrictions should continue with caution. An
understanding of the risks associated and consideration of proper maintenance activities
to establish trees during these periods is crucial.
- Prudently planting trees can replace drought stressed and dead
trees, which can help reduce the negative effects of drought on the landscape.
- Keeping trees in the landscape helps reduce soil erosion,
stabilizes soils, significantly reduces storm water runoff and shades landscapes and
structures to help minimize water and energy use.
- Factors to consider when planting trees and shrubs include soil
conditions, available space above and below ground, exposure, moisture and light
- Planting smaller trees (2 inches or less caliper for deciduous
trees and 6 feet or less height for evergreen trees) reduces the investment and risk of
planting during drought periods, can establish a tree more quickly than planting a larger
tree and will require less maintenance over time.
- Select from species that are hardy to the region and fit well with
the Xeriscape principles of maintaining an attractive landscape with minimal water use.
- Proper mulching and adherence to watering guidelines for trees and
shrubs will help establish newly planted trees in times of drought.
Why you should plant trees and shrubs during times of
Plant trees and shrubs during
times of water restrictions can be risky. Watering
restrictions are in place and establishing trees in a semi-arid region is difficult enough
without an extended drought to contend with. However,
by eliminating all tree planting we will be missing many opportunities to keep our urban
forest alive and vital in our region. It is
critical to not only have a diverse set of species in the landscape but also a diversity
of age among those species in the landscape. This
means planting new and replacement trees each year, especially during times of drought, to
replace trees and shrubs that will be lost to age, injury and other causes.
Plant with care and prudence
during times of water restrictions. Using
smaller trees (2 inches or less caliper for deciduous trees and 6 feet or less height for
evergreen trees) minimizes the investment risk and can also lead to earlier establishment
and lower maintenance of the plantings over time. Carefully
planting trees and shrubs will preserve the resources that are critical to maintain soil
stability, reduce soil erosion, control and utilize storm water runoff, shade our
moisture-starved lawns and reduce energy usage by shading homes in summer and blocking
winds in winter. A well-stocked urban forest
also acts as an air filter and purifier, absorbing carbon dioxide and emitting oxygen to
help provide cleaner air.
Finally, planting trees and
shrubs during times of water restrictions will help increase the visibility of a diverse
set of species that tolerate our environmental conditions in this region and fit well with
Xeriscaping (low water use landscapes).
Back to Top
Selection - if the
landscape calls for planting trees, buy them 2 inches or less caliper for deciduous trees
and 6 feet or less height for evergreen trees. Don't invest in large trees that may die
because they can't be adequately watered. Smaller trees require less water to get them
Available space - both in terms of soil rooting
area and airspace - a mature tree develops a root system that extends well beyond its
branch extremities. A healthy mature tree has much more biomass in its root system than
its above-ground leaves, branches and twigs. Big trees need large rooting areas. For
example, a honeylocust planted in a narrow parking lot planting bed is essentially doomed
to a short and stressful life. Trees that grow to be large should not be planted too close
to other trees, garden areas, buildings, sidewalks or to a property line, where they would
encroach upon adjacent properties. Trees that grow to be large should not be planted under
utility lines or within prescribed distances from them. Before planting in areas with
underground utilities, contact the Utility Notification Center of Colorado at
Moisture - many tree species thrive where
rainfall exceeds 30" annually. The Denver area receives 14-18" annually, so
supplemental water is needed for many landscape trees. Humidity is very low in the Denver area;
many species prefer higher relative humidity. On a smaller scale, the wetter, low-lying
areas of a property can support different species than higher and drier spots.
Exposure - north-facing slopes are cooler,
moister and retain snow longer than south-facing slopes; east-facing slopes are cooler and
moister than west-facing slopes. Similarly, the north and east sides of a house are often
more conducive to certain tree species than the west or south sides. For example, maples
prefer cooler, moist soils - so they grow better on north or east exposures. The reflected
heat and dryness of a south exposure is better suited for other species.
Light - most trees prefer full sunlight; many can
tolerate partial shade. A few species known as "understory" trees are usually
smaller trees that grow in the shade of larger trees in their native habitat. Note that
some cultivars (horticultural selections) that have variegated leaves may
"scorch" in the high-intensity sunlight of our mile-high area; these may fare
better in partial shade or on east exposures.
Plant Grouping - Plants
in the forest and other natural settings are often found in communities of
like plants. There is strength in numbers. This concept is applicable to landscape
gardening as well. Grouping plants with similar cultural requirements and water needs
makes watering and maintenance easier. Plants in groups are generally more likely to
thrive than individual plants sprinkled throughout the landscape.
Back to Top
Many plants are commercially available that
may survive with extra care and attention, but are not necessarily well suited to a
semi-arid climate. Plants appropriate to this climate will require less water, be less
susceptible to pests and disease, and live longer than plants not suited to the semi-arid
west. A list of regionally appropriate plants is provided below:
Back to Top
Development of new themes in landscaping
using dryland or xeric principles is radically different from the traditional approach to
landscaping as it has been commonly practiced in the Front Range area. The Front Range is
semi-arid, and we are just coming to grips with just how semi-arid it is. Xeric plants are low to moderately low water use
plants in the landscape. Be aware that even
low water use plants must be watered well in order to become established. Once established, xeric plant materials need much
less water and maintenance than plants not suited to semi-arid conditions.
The traditional approach using vast
swaths of bluegrass lawn in conjunction with small and peripheral shrub and perennials
beds along the edges needs to be rethought. A
more practical solution will reduce water usage dramatically and will retain an attractive
and vibrant landscape. One goal of revising our landscape water needs is to save existing
trees and shrubs, plants that have been in the Denver landscape for years. Dryland
landscape schemes provide the homeowner with options that can be used to create a
landscape that is water wise from the beginning and offers an attractive alternative to
expansive areas of lawn.
Back to Top
The following are suggestions on how to
keep a landscape attractive and water efficient.
Shrub Beds - enlarging beds
under trees to the edge of their drip lines, extending shrub and perennial beds outward
from along the edge of the house reduces the amount of bluegrass lawn as a percentage of
the overall landscape.
Soil Amendments prepare
tree and shrub beds by adding compost to the soil. This
improves soil texture and adds essential nutrients that plants use. Adding organic matter
to the soil helps it retain moisture as well.
Irrigation Systems - redesign
sprinkler systems to achieve an efficient irrigation system. Drip irrigation systems apply
water directly to the soil and are very efficient.
Plant Selection - install
dryland plants in the tree and shrub beds. There are many attractive and colorful
perennials and versatile groundcovers that are low water users in addition to the trees
and shrubs listed above. Grouping plants with
similar cultural requirements and water needs makes watering and maintenance easier.
Back to Top
Using an organic mulch such as wood
chips, bark, leaves and evergreen needles around trees and in shrub beds will provide
several benefits. A four inch layer of mulch under trees and around shrubs and perennials
goes a long way to keep plants alive and healthy. Mulch helps to regulate soil temperature
resulting in less stress on plants between hot, dry summer days and freezing winter
nights. Mulch allows for less and easier weeding of beds. Organic mulches, as they
gradually break down, add nutrients to the soil. Mulching
around the base of trees also keeps the lawn mower and weed eater from damaging the bark
Most importantly, mulching reduces water
usage. A mulched area under low-water-use trees with dryland shrubs or perennials can
reduce water usage by as much as 50 percent from
the water needed to maintain a bluegrass lawn.
Mulching mature trees to their drip line
is beneficial as well. For a larger-sized tree this may extend a mulch circle outward from
the trunk 20 feet or more, greatly reducing the amount of lawn. Having mulch to that point
helps retain moisture in the root area.
Back to Top
Back to Top
Photo: Judy Sedbrook
to Gardening in a Dry Climate
Back to Home