Weed control / autumn

Asked September 28, 2014, 2:14 PM EDT

Hi, I have weeds that I believe have gone to seed in my xeriscaped yard in Colorado Springs - they look to be purslane and spurge groundcover type weeds. I'd like to "get ahead" of these weeds for the coming year if I can - what are my options?

  • Should I leave them alone -- frost will take care of it? Use preemergent in the early spring to try to curtail their return?
  • Should I pull them? Now or after they dry out a little more?
  • If I pull them, is there something - preferably all natural - that I should put down to prevent or curtail their regrowth in the spring?
  • I have mulch, through which all of these weeds are growing. Should I remove the mulch before putting anything down (such as a preemergent - whether it's now or in the spring)?
  • One other idea I had - I could pull the weeds, rake up the mulch, put down newspapers or corrugate / cardboard and then put mulch back over that.

I appreciate any insight you can offer.

El Paso County Colorado weeds

1 Response

Thank you for your questions.

Unfortunately weeds will spread – that is their nature.

Prevention is the most powerful form of weed management. One of the best ways to prevent weeds from spreading is to control existing infestations. Fall is a good time to exert weed control. Herbicides are the primary tool of choice in the fall. Biological control agents generally have finished preying on weeds by fall.

Mowing (or weed whacking) and hand pulling are most effective when practiced before weeds go to seed. Biennial weeds, such as musk thistle and diffuse knapweed, are in the rosette growth stage (except those setting seed) and can be readily controlled with herbicides.

Perennial weeds, such as Canada thistle, Russian knapweed, and leafy spurge, also are very susceptible to fall-applied herbicides. The physiology of these latter weeds changes as the day length continues to shorten and temperatures decrease. It is not fully understood how these changes increase their susceptibility to herbicides applied in fall, but gardeners can seize the opportunity and take advantage of this fact.

The growing season is not finished, so make your fall weed management plans and take advantage of their susceptibility to control methods this time of year.

HOWEVER! Before you decide to apply an herbicide, properly identify weeds. A couple of hard frosts will kill some weed species, which means herbicide treatments are not only unnecessary, they're wasteful. These weeds include broadleaf summer annuals such as purslane, knotweed and pigweed; and grassy summer annuals like crabgrass, goose grass, barnyard grass and foxtail.

Fall herbicide sprays effectively kill such weeds as dandelion, plantain, thistle and bindweed. Use products that contain 2,4-D, MCPP, MCPA, triclopyr and clopyralid.

Where practical, it's best to apply herbicides directly to affected areas only rather than broadcasting the herbicide. Always read the label on an herbicide product before purchasing, before spraying and before cleanup.

In early March, next year it is the perfect time to spread a pre-emergent over the areas you speak of. PREEN is a good one to use.

Thanks again for your questions.