Clear plastic mulching (solarization) is effective for eradicating crabgrass
plants and seed if it is applied during periods of high solar radiation. In
California's Central Valley, this means during June to August, whereas in
coastal areas the best time may be August to September or May to June when
fog or wind is most likely to be at a minimum. Before applying the plastic,
closely mow the crabgrass, remove the clippings, and water the area well. It
is not necessary to cultivate before solarization, but a shallow cultivation
may improve control. Place clear, ultraviolet (UV)-protected polyethylene
over the area for 4 to 6 weeks. Shade will reduce the effectiveness of
solarization because it limits the amount of radiation. Solarization works
most effectively when there is no slope in the land or if there is, the
slope has a south or southwest exposure. Temperatures are not as high under
plastic placed on a north-facing slope; consequently, control is not as
effective. After solarization, do not cultivate the area deeper than 3
inches to avoid bringing weed seed into the upper soil layer. (See the soil
solarization publication listed in Reference.)
Consider cultivation to improve control
Cover area with plastic
Anchor it somehow so it doesn't blow away
Leave it there for 6 weeks
Spray area with Roundup
Crabgrass is dead in a week.
I know which plan I'd go with.
Right. The idea is to kill the crabgrass, and only the crabgrass,
before it produces seeds. If you attempt to do this by mowing, be sure
you use a catcher to pick up all the clippings and seeds. FWIW, I
just use Bonide "crabgrass killer". It took three applications this
year but I don't think I'll have to use preemergent crabgrass killer
Roundup it almost always the wrong thing to use for crabgrass. It kills
absolutely everything green and will leave gaping spots in your lawn.
If you look at the OP, the suggested method of using plastic ground
cover for crabgrass was obviously for use in an area where the goal
was to kill everything, unless you think grass will survive 6 weeks of
being covered by plastic. For that application, Roundup is the best
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