pre emergent herbicides

Debbie Polson
by Debbie Polson
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 Douglas Hunt on Apr 04, 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: http://www.ext.colostate.edu/pubs/garden/03101.html And here are some specific pointers on Russian knapweed: http://www.ext.colostate.edu/pubs/natres/03111.html
  • Debbie Polson Debbie Polson on Apr 05, 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?