University of Vermont Extension
Department of Plant and Soil Science
TURF WARS—TREES AND LAWNS
Dr. Leonard Perry, Extension Professor
University of Vermont
A common problem in many landscapes is the competition of trees and
lawn for the same light and resources. In many home landscapes,
what began as a lush lawn with small trees has become a thin and
weedy lawn shaded by many large trees. By knowing what both trees
and lawns require for site and maintenance, you can determine if you
can have a lawn in the shade of trees and, if so, how.
Both trees and lawns are not only attractive in landscapes, but
serve many functions. Both trees and lawns produce oxygen, cool the
air, stabilize dust, trap air pollutants, and help control erosion.
In addition, trees provide shade for buildings in summer and
windbreaks, they provide habitat and food for wildlife, and harbor
many insects that birds need for food. Lawns provide a groundcover
for lower traffic areas, a place to walk and play and entertain.
Both trees and turfgrasses compete for water, nutrients, and light.
By reducing this competition, you may be able to have both.
Turfgrasses, like many trees, also need good soil drainage to grow
Most lawn grasses will not grow well if they get less than 50
percent (less than 4 to 6 hours per day) direct sun. One solution
to allow more light to grasses below trees might be to eliminate
some trees, perhaps weaker and spindly ones. Or you might remove
some limbs to allow more light to reach the ground below. If trees
are large, this is often a job best left to an arborist. Even
removing some lower limbs will allow more light and air, so lessen
Another option might be to choose more shade tolerant grasses. Fine
fescues (such as red, Chewing, hard, and sheep fescues), as well as
rough bluegrass, are the most shade tolerant. Fine fescues prefer
drier soils and don’t tolerant continually wet soils. For moist,
shaded areas consider a rough bluegrass such as the variety Sabre,
or supina bluegrass. For moderate to light shade, you can grow tall
fescue (the coarse leaf texture doesn’t make it great for home
lawns), or some Kentucky bluegrasses such as Glade or America. You
may be able to find a seed mixture formulated for shade. Keep in
mind, though, that just because a grass or mixture is listed for
shade doesn’t mean it will grow perfectly well in dense shade.
While shade above ground is the most obvious limiting factor for
grass under trees, the below ground tree roots are equally important
to consider. Most tree roots are in the top two feet of soil,
contrary to what many think, and most the finer roots that absorb
water and nutrients are even more shallow. Grass roots in the full
sun occupy much more soil than tree roots, which can be a problem if
planting young trees. But under mature trees, the grass is thinner
and the roots less dense, so they compete poorly with these tree
Since grass doesn’t grow as vigorously under trees as it does in
full sun, the common recommendation is to fertilize at about half
the normal rate, or about two pounds of actual nitrogen per 1000
square feet. Fertilizing in fall, after leaf drop from trees,
benefits grasses as they are somewhat active then compared to the
trees going dormant. Another time you might fertilize grasses is
early spring, about a month before leaves appear on trees. Don’t
use fertilizers containing herbicides, as they can be taken up by
tree roots, and weaken trees over time.
Avoid high nitrogen fertilizers, as they promote succulent top
growth. Best are ones with higher potassium (the third number on a
fertilizer bag) as this promotes stronger blades more tolerant to
wear, and decreases disease susceptibility. Most soils contain
sufficient phosphorus (the middle number on a fertilizer bag), so
unless called for by a soil test, try not to add this. Excess
phosphorus washes into and pollutes waterways in many cases. Many
prefer low analysis, organic fertilizers (such as 5-3-4), with their
nutrients released over time.
Good culture and the right conditions will help reduce weeds,
without using herbicides. A common lawn weed, mosses, indicates the
soil is too moist and poorly drained, compacted, with low fertility,
acidic, or a combination of these.
In addition to nutrients and light, water is the third factor needed
by both lawns and trees. If rain does not measure an inch or more a
week, or consists of light showers, water deeply but infrequently.
Frequent, shallow watering leads to surface roots that dry out
quickly during drought or under tree roots. In my own landscape,
soil moisture under trees can be 30 to 40 percent lower (35 to 35
percent soil moisture) than in full sun areas without tree
In addition to dealing with these three main competing factors, mow
lawns under trees higher (one-half to an inch higher) than those in
full sun. As with any mowing, do so regularly, not removing more
than one-third of the blades at any one time. Leave clippings to
replenish nutrients and organic matter back into the soil. They
won’t cause thatch buildup.
Minimize foot traffic on shaded lawns, as they can’t recover as well
as those vigorously growing in full sun. Remove leaves and branches,
particularly in fall, promptly. Grass in the shade needs all the
light and water and air it can get to avoid stress and diseases.
You may need to “overseed” (sow more seeds on top of the existing
grass) in early spring every year or two.
If planting new trees in a lawn, make sure they have plenty of space
to grow over time, and are far enough (40 to 100 feet for many)
apart to allow plenty of light between them. Avoid trees with
shallow roots, such as beech, maples and willows. Avoid trees with
dense canopies if possible, such as oaks and maples. Lindens
(basswood), ginkgo, birches, and poplars are good choices for
planting near lawns. On the other hand, if establishing a lawn near
trees, don’t till the soil as this will damage the shallow tree
In spite of your best efforts, if a lawn just doesn’t perform as
you’d like under trees, consider just placing bark mulch under the
trees out to below the edges of branches (the “drip line”). At a
minimum, placing mulch around trunks, but only an inch or two deep,
will keep mowers and weed trimmers from damaging the tender tree
bark. Don’t make a “volcano” of mulch up around tree trunks, as this
can smother bark and harbor insects.
If you can’t grow grass in the shade, but want plants and not mulch
in an area which won’t get foot traffic, consider groundcover
perennials. If such areas are large and you want to walk through
them, consider a combination of groundcover with mulched paths.
Perennial vinca (where not root invasive), pachysandra or spurge,
creeping foamflowers, lily of the valley, barren strawberry, ferns,
and ajuga or carpet bugle might be used. Just make sure they don’t
escape into adjacent lawn areas, as some like the carpet bugle can
take over these areas too.