Weed-killer in winter?

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on December 08, 2011 at 9:09 AM, updated January 16, 2012 at 9:15 AM work best in warmer weather when the weeds are actively growing.

   Q: I have peonies, and the bed is infested with a low-growing, underground-spreading weed. It is impossible to pull. Would it be safe to use Roundup now that the peonies are dormant and the weed is still green?

   A: Once the peonies are dormant and cut to the ground, they should be safe from any damage by Roundup (glyphosate) -- the most popular kill-everything-green herbicide.

   However, Roundup also is unlikely to have much, if any, impact on the weeds now. Roundup works best when plants are actively growing and ideally in a temperature range of 60 to 90 degrees.

   Even though your weed is still green, it's not growing actively enough now for the chemical in Roundup to move from the leaves to the roots, where the kill would happen in-season.

   You could try a little as a test to see if anything happens. My guess is not -- or not much. I think we're a bit late now, but temperatures have been fairly warm still for this time of year.

   You'll probably have better success waiting until spring and then using a sponge or paint brush to apply Roundup to the weeds. That lets you get the chemical on the weeds more accurately without getting any on the peony leaves. So long as you don't get any on the peonies, Roundup applied to weeds underneath won't significantly harm the peony roots.

   For big weedy patches, I've seen people use a long-handled mop to dip into a bucket of Roundup and brush over the tops of low weeds. You don't even have to bend over that way.

   Be sure to wear rubber gloves so you don't get Roundup on your skin. And be careful you don't let Roundup drip on anything you don't want to kill.