University of Vermont Extension
Department of Plant and Soil Science
Anytime News
Article
RECLAIMING A FLOODED YARD OR GARDEN
Dr. Leonard Perry, Extension
Professor
University of Vermont
Across the country,
weather events in recent years have resulted in many flooded areas.
Hurricane Irene in August, 2011 caused epic
flooding in Vermont and other northeastern states. If you were
affected, and are lucky enough to
still have a home and yard, your lawn and garden may be buried under
silt. How you deal with a landscape buried under
silt depends on its depth.
As with any soil, make sure it is
dry before working with it. Soil should
form a ball in the hand, then crumble when pressed. If the squeezed
ball of soil drips water,
it’s still too wet.
If
a lawn is covered with under an inch of silt from flooding, it may
recover. Scratch the surface with a
steel hand rake or similar tool. I have
a mini-tiller with vertical blades just for penetrating compacted
soil (similar
to a “vertical mower”). This will allow
water and air to penetrate below a crusted surface to the roots.
Once the silt is broken up on lawns, for
smaller areas you can try washing silt from the lawn, or at least
thinning the
depth, with a forceful garden hose. If
the silt dries and crusts, keep it broken up during the season until
the grass
gets reestablished.
As
soon as possible in the season, do a soil test to see what nutrients
may have
washed away or need replacing. Kits are
available from your local Extension service office, complete with
sampling
instructions. Results will tell major
nutrients needed, amounts, and if soil acidity (pH) needs
correcting.
If
your lawn is covered with more than an inch of silt, it may not
recover and
need to be reestablished from
scratch. Fine leaf fescue and perennial
ryegrass have poor tolerance to submergence from flooding,
especially if they
were under water for 4 days or more. If
under three inches of silt, you can try renting an aerator to use up
to 6 times
through the season. This removes small
cores of soil and silt, allowing air and water to get to the roots.
If you do this on a smaller area, you can
topdress sand or compost on top, which will work into these holes.
If the silt
is over 3 inches deep, consider having it professionally removed
unless you
have a tractor and attachment to scrape it off.
If
the silt is just too deep or your efforts are in vain, and the lawn
isn’t
showing signs of growth by late spring, you should probably just go
over it
with a rototiller incorporating the silt as if adding a layer of
topsoil. Make sure and soil test to see what needs
adding before reseeding. If a small area
or you want instant results, and have the budget, consider adding
strips of
sod. If this is not possible, keep in
mind that the best times for seeding cool season grasses are early
spring and
late summer when conditions favor them and not the weeds. If this
is the case, you can stabilize the
soil by seeding annual ryegrass at 4 to 6 pounds per 1000 square
feet. Then till this in late summer before seeding
the permanent grasses.
Another
option would be to spend this first year rebuilding the soil,
removing as much
silt as possible first. Since the silt
likely brought in a load of weed seeds, you’ll likely need to deal
with
them. After appropriate steps as above,
rather than replant, add clear plastic to “solarize” the soil. This
is basically covering the soil with a
mini-greenhouse which heats up, killing some diseases and many weed
seeds. The soil could then be tilled again, bringing
more seeds to the surface, and covered again.
Or, after the first covering, when uncovered seed in a cover crop.
Solarization
is simple. Best done in May or June as
the soil is heating, rake the soil, moisten it with the hose if dry
(moist soil
holds more heat), then cover with a thick sheet of clear plastic.
Hold the edges down with boards, stones, or
just bury in a shallow trench. Leave on
for 6 to 8 weeks.
If you have eroded areas to deal
with, refilling and replacing the topsoil is ideal. If this is too
expensive, amend any added
backfill with organic matter such as peat moss, compost, rotted wood
chips or
old mulch, or similar. If the area isn’t
destined to be a lawn, you can either add plantings (perennials or
shrubs) and
mulch, seed with annual rye, or add a cover crop such as clover.
For trees and shrubs, make sure to
scoop or rake away silt deposits from the base of plants and tree
trunks. Even 6 inches deep around trunks, or 3 inches
deep over roots, can be enough to smother them, resulting in a slow
plant
decline and perhaps eventually death.
Water and air need to reach tree roots, and since many of their
feeder
roots are near the surface, you’ll need to break up or remove silt
as described
for lawns. Just don’t till under trees
through, as this will damage their surface roots.
Some trees that originated in
floodplains survive such conditions, such as river birch and
willows, but
others such as pines and oaks may suffer.
Many trees are able to withstand up to a week of flooding.
Unfortunately, trees may take several years
to show flood damage symptoms, and then it is too late to save
them. If you have a special tree, consult with an
arborist to see if corrective measures are needed now
As much silt as possible should be
removed from vegetable gardens, and used to backfill eroded areas or
perhaps
make a berm garden for flowers. Make
sure to use a forceful hose to wash all such silt away from the root
areas
under bush fruits such as blueberries and brambles. A general rule
is that you should not harvest
produce within 120 days (4 months) of flooding, as it may be
adulterated from
contaminants. This does not apply to
crops submerged from “ponding” or standing water
such as from rain, that did not wash in from elsewhere.
For annual flower beds, remove as
much silt as possible, or till in as described for lawns. For
perennial
flowers, many are tough and can emerge through a few inches of
soil. Shallow-rooted ones such as yarrow and
tickseed, or groundcovers such as dead-nettle and sedum, likely wont
survive
being buried. If you know generally
where these are, dig them in spring and replant higher or in
refurbished soil.
Even though many perennials will emerge
through a few inches of silt, it helps to rake over them in early
spring, or
around them later, to remove some silt and to keep it from
crusting. As with lawns and other beds, make sure to
test the soil fertility. If more than a
few inches of silt, try to remove as much as possible in early
spring before
plants start growing. Otherwise they either wont emerge, or you’ll
destroy
them later in the process of silt removal.
For deeply covered perennial beds, if you can find choice plants, it
may
be easiest to dig them up, then till the whole bed and start over as
with lawns
(a chance for a new design and new plants).
If
working soil that was flooded last year, or even a couple weeks
prior,
generally it is safe since sun, soil organisms, and rain all work to
destroy
harmful bacteria in sediment. Just watch
for any debris that may have washed in, or contaminants still
lingering such as
oil or chemicals. Also watch for signs
of the invasive Japanese knotweed that may have washed in. If you
suspect contaminants, contact your
local town officials or health department, and follow precautions
outlined
online by the Vermont Department of Health (healthvermont.gov).
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