ISSUE 10  July 6, 2000

TOO MUCH RAIN MORE OF A CURSE WITH GARDENS AND TURFGRASS
THAN TOO LITTLE

    The gardens in the Fargo-Moorhead area and likely throughout much of North Dakota, have fared
poorly so far this year with the frequent and heavy rainfall events. The ripple effect (no pun intended!)
of all this water is being realized as the summer days pass. When soil is at field capacity, all the pores
are filled with water, and no air space is available for gaseous exchange in the root zone. The same
problem exists when the soil is flooded. The longer this condition exists the greater the potential for
problems to develop.

    The flooding of soil compacts it and often plugs micropores with silt. Hence, when the water finally
drains or evaporates, the silt has clogged the pores, contributing to anaerobic conditions around the
roots. It is a good idea to carefully cultivate the soil around the roots of vegetables and flowers, as this
breaks up the silty crust that effectively seals the soil from any significant gas exchange. If the soil and
root zone can be dried quickly enough, root rot can be avoided.

    Turfgrasses will benefit from a core aeration and/or power raking later this summer or early fall.
As with cultivating around the flowers and vegetables, this practice breaks the "silt barrier" that
keeps the roots from exchanging gases of respiration necessary for good turfgrass growth and health.
Reseeding of dead areas can be carried out anytime. Power-rake or core the areas to a crumb-like
texture, and seed with a quality bluegrass mix.

    Of course, if the turf area had debris moved on to its surface as a result of the heavy rains and
subsequent flooding, this should be removed first, to facilitate mowing and sunlight reaching the turf
canopy. If off-site soil moved onto the turf and made a deposit of 2 inches or more, such soil should
be removed quickly to prevent the buried turf from being killed. If there is any evidence of salt on the
surface of the grass, it should be washed off as soon as possible to prevent injury.

    Turfgrass species vary greatly in their submersion tolerance. A red fescue lawn can be killed in
one day from submersion at 86 degrees F. A turf may survive as long as 60 days at a temperature
of 50 degrees if it happens to be Toronto creeping bentgrass. Those grass species that are rated as
either excellent or good for submersion tolerance are: Rough bluegrass, Timothy, Creeping bentgrass,
and Buffalograss. Kentucky bluegrass, crested wheatgrass, and perennial ryegrass are fair at
submersion tolerance, while red fescue is rated as poorly tolerant of submersion.

    Evidence of flood damage is typically a reduction in growth or clipping yield, a yellowing of the
foliage, and invasion of weeds or pathogens, due to a lack of turfgrass vigor. This can be corrected
with a core aeration followed by an application of nitrogen fertilizer.

Ron Smith
NDSU Extension Horticulturist and Turfgrass Specialist
ronsmith@ndsuext.nodak.edu