Fall is for Lawns
By: Sandy Feather
©2006
Penn State
Cooperative Extension
Q.
We have an
older lawn that is in sad shape. We would like to know if it is
worth repairing, or should we just start over? Also, what is the
best time to renovate or start new lawns?
A.
Fall is the
best time to undertake lawn renovation, overseeding jobs and
installation of new lawns. Air temperatures are cooler and less
stressful to our cool-season turfgrasses, while soil temperatures
are warm enough for rapid seed germination and root development.
There is far
less weed pressure on fall lawn seedings because most weed seeds are
"programmed" to germinate in spring. Besides, a frost will kill many
tender weed seedlings without harming grass seed or seedlings. Fall
is also a great time to get lawn weed problems under control,
especially tough-to-kill perennial weeds such as ground ivy.
The first step
is to determine what is wrong with the lawn. Lawns go downhill for
many reasons, including:
- improper
mowing
- soil pH
(acidity/alkalinity) too high or too low
- lack of or
improper fertilization
- lack of or
improper irrigation
- too much
shade
- competition
from tree roots
- turfgrass
species not adapted to the site
- heavy
thatch layer
- soil
compaction
- poor
drainage
- insect or
disease problems
- the weeds
are winning
A good place to
start is with a soil test. Inadequate (or excessive) fertilization
can limit turf growth. A soil test will tell you what type of
fertilization program is required. It will also tell you what you
have to do to get your soil pH into the optimum range of 6.5 to 7.0
that most turfgrasses prefer. Soil test kits are available from your
local Penn State Cooperative Extension office.
Mowing practices
greatly determine the quality of turfgrass. If you allow your lawn
to grow too long, then cut it short, you are not doing it any
favors. Most species of turfgrass should be cut at a height of 2 to
3 inches. The longer the grass, the more extensive its root system.
If you do not
water your lawn, drought years past and present have probably taken
their toll. Deep infrequent watering during hot, dry weather is
important to maintain a healthy lawn. Deep watering encourages the
turf to develop a deeper, more extensive root system. Conversely,
frequent shallow watering encourages a shallow root system that is
stressed during droughts.
Use a sprinkler
or an irrigation system to apply 1 to 2 inches of water weekly to
your lawn if we are not receiving any rain. This is best applied in
one long, deep soaking session. Our clay soils can absorb only about
1/2 inch of water an hour, so it should take two hours of watering
to apply an inch of water.
To measure how
long to run your sprinkler or irrigation system, take a
flat-bottomed container such as a coffee can and mark off half-inch
increments. Place the can where it will be hit by the water, and
time how long it takes to gather a half-inch of water. (You may want
to place several cans because your sprinkler may not distribute the
water evenly.) Then run your sprinkler twice as long.
You may need to
apply water even more slowly to steep slopes to avoid wasting it to
runoff. It is best to water in the morning. If you water during the
heat of the day, too much water is lost to evaporation; if you water
at night, the grass stays wet too long and may be more likely to
have disease problems.
Most grass
species prefer full sun. If your lawn is heavily shaded, you may
need to remove or limb up some of the trees to allow more sun to
penetrate. You may also wish to overseed with fine fescues such as
creeping red fescue, hard fescue or Chewings fescue. They are the
most shade-tolerant species of turfgrass adapted to our climate. The
newer turf-type tall fescues perform reasonably well in shade, too.
Also, trees
compete with turf for water and nutrients. Turf grown under such
conditions should be watered more frequently and fertilized at a
heavier rate than turf that does not have such competition. Often,
shade-tolerant groundcovers such as barrenwort (Epimedium spp.),
ferns, Allegheny foamflower (Tiarella cordifolia),
pachysandra or creeping myrtle (Vinca minor) are better than
grass in such a situation.
Older lawns
frequently have thick thatch layers. Thatch is a tangled mat of
organic matter that accumulates between the soil surface and the
grass. Just as we slough off dead skin cells that are replaced by
new ones, turfgrass plants slough off dead roots and stems. When
these accumulate faster than they break down, a thick thatch layer
can build up. How quickly thatch accumulates depends on:
- The variety
of grass in your lawn. Kentucky bluegrass and creeping red
fescue spread by underground stems (rhizomes) and tend to build
up thatch faster than bunch-type grasses such as perennial
ryegrass, turf-type tall fescue and Chewings or hard fescue.
- The pH of
your soil. Soil-dwelling microbes that break thatch down are
inactive when the pH falls below 6.5.
- Mowing
practices. Letting your grass grow long, then cutting it short
will create more dead roots and stems that end up adding to the
thatch layer. Also, leaving very long grass clippings on the
lawn on a regular basis will cause thatch to build up. However,
a properly used mulching mower does not contribute to the thatch
layer because it cuts the clippings into very fine pieces that
break down quickly.
-
Over-fertilization. Too much fertilizer causes the grass to grow
more quickly than normal and also speeds up the process of
sloughing off dead stems and roots, which contribute to thatch
build-up.
- Compacted
soil prevents the roots from penetrating deeply. Shallow roots
dry out and die faster and add to your thatch woes.
A little bit of
thatch, say a half-inch or so, is actually helpful. It acts like a
mulch to conserve water, moderate soil temperature and shade out
germinating weed seeds.
A heavier thatch
layer becomes a breeding ground for disease and insect problems and
interferes with treating root feeding insect problems, such as white
grubs.
Up to 2 inches
of thatch can be removed with a power dethatcher, often available at
tool rental shops. Or hire a lawn service to do it.
Run the power
dethatcher in one direction, then again in the perpendicular
direction. It is important that the tines get through the grass and
thatch layer and down into the soil. A properly dethatched lawn
should make you want to cry because it is so badly torn up.
Overseeding will help it recover.
Dethatching
should be done in fall only so that your lawn has ample time to
recover. There are limitations to what dethatching can accomplish.
If you have a thatch layer more than 2 inches thick, consider
starting a new lawn.
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