We have had a serious crabgrass problem since we bought our house. This is on a slope that we don't want to have to mow and are looking at wildflowers as something that could out compete the crabgrass.

Will pre-emergent used to kill crabgrass (basically our entire lawn) also kill our new wildflower seeds? Having trouble finding this answer on google.

  • IMO preventing crabgrass seeds from germinating is a battle not worth fighting. I moved into a suburban home that was pretty bad. I just let it all come up for a few years. I hand pulled large clumps and mowed them into the thatch with the walking mower as I mowed. I sprayed large areas with selective herbicide. After a few years, the number of seeds in the soil finally dwindled.
    – Evil Elf
    Commented Jan 12, 2021 at 13:48

1 Answer 1


Pre-emergent weedkillers work by disrupting the root growth of newly germinated seeds, so that the seeds germinate and then die. The length of time it stays active in the soil depends on the formulation of the brand that you buy.

Crabgrass germinates over quite a wide soil temperature range, so a brand that is intended for crabgrass will presumably stay active in the soil for a long time (i.e. several weeks).

It will not affect plants that have already germinated and are growing, but if your wildflowers are annuals which produce seed and then die each year, it will kill the wildflowers as they germinate.

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