Asked on Apr 3, 2013

pre emergent herbicides

Debbie PolsonDouglas Hunt


I would like to use a pre emergent herbicide in my garden, but I don't know when or how, then when can I replant with what I want. What is the best method. Also HOW do I kill russian knapweed? I've tried everything.
2 answers
  • Douglas Hunt
    on Apr 4, 2013

    Debbie, pre-emergent herbicides should be applied in early spring, before weeds start germinating. When the forsythias bloom is generally a good indicator. There is no impact on transplanting, as pre-emergents work solely by suppressing germination. This article from Colorado State addresses the use of pre-emergents in lawns, but the principals are the same for the flower garden: And here are some specific pointers on Russian knapweed:

  • Debbie Polson
    on Apr 5, 2013

    Thanks so much for the link...I have tried many things for the knapweed and nothing seems to work well. How soon after applying a preemergent in a garden site could seeds then be planted? How long is the herbicide active?

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