Here is your gentle reminder that if you’re planning to put down a pre-emergent herbicide to control grassy and broadleaf weeds in your lawn, NOW IS THE TIME.

I know, I know…as spring warms up, the last thing we want to be thinking about is herbicides. We’re ready for flowers! But mid-March through early April is your window of opportunity for dealing with these weeds, depending on the weather. And this year, the weather has been warm early, so earlier application might be wise. If the seeds of crabgrass, new dandelions, purslane, spurge, etc get a chance to germinate before you apply the pre-emergent herbicide, you’ve lost the battle for this year and will have to deal with the full grown versions of these weeds later, either by digging or using other herbicides. (And in the case of crabgrass, neither of those options is going to have much effect.)

Pre-emergent herbicides work by killing the very young seedlings of weeds, just after they germinate. The herbicide needs to be on the soil before these seeds germinate. Water it in well to make sure it is washed off of grass leaves and directly contacting the soil. These herbicides WILL stop any new grass seed from establishing too, so if you’re planning to overseed your lawn this year, you must wait until late summer to do so.

If you have a lawn (especially a new lawn) of a warm season grass, such as blue grama or buffalo grass, applying a pre-emergent can be very effective in stopping the cool season weeds that get a jump on growth before the grass comes out of dormancy and starts to grow.

As with any herbicide, be sure to follow the instructions on the label for the one that you buy. Applying heavier-than-recommended rates can damage other plants’ roots, including grass roots in a lawn.

For more information on controlling difficult grassy weeds in your lawn, see Colorado State University Extension’s Fact Sheet 3.101 – Control of Annual Grassy Weeds in Lawns.

Contributed by Carey Harrington, Certified Colorado Gardener

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