Trust Me, It's Not Crabgrass

Poa annua, or annual bluegrass, appears bright green
with a white seed head

Think you have crabgrass in your lawn? Let me be blunt: you're wrong. Here in the Pacific
Northwest, crabgrass is rarely a significant problem in lawns; in fact, even when it is you won't notice it showing up until summer heat sets in. The fact is, if you think you have crabgrass in your lawn during the cooler spring months, it's not crabgrass at all. It's poa.

Somewhere back in lawn care history, someone thought they'd sound smart if they walked into a nursery and asked for a weed killer that would take care of crabgrass in their lawn. It's the gardening equivalent of walking into your doctor's office with the wealth of knowledge you found on WebMD. You'll sound smart, but the diagnosis is way off.

Don't fault yourself, though--for better or worse, the term "crabgrass" has come to be used among gardeners today to describe a broad range of grassy weeds. The fact of the matter is, however, that the grassy weed you're probably fighting in March, April and May is a different beast altogether, and it's called poa annua, or annual bluegrass.

Poa is a cool-season grass, meaning it typically goes dormant during the heat of summer. This time of year, though, it's rampant in spreading through our lawns. You'll notice poa by the lighter green color of its foliage, a slightly broader blade than typical lawn grass, and a bright white seed head that appears while the grass is still short.

It's that aspect--a seed head at a very low height--that allows poa to spread so readily. Even mowing your grass short will often miss most of the seed heads, and it regenerates so quickly that it will often go to seed just a few days after mowing.

So, now that you know it's not crabgrass, what steps can you take to eliminate it from your lawn? Sadly, to date there's no total cure; since poa is so genetically similar to lawn grasses, most weed killers that outright kill poa would also kill your lawn.

The best method to eradicate poa is prevention. Since poa is considered an annual grass, it won't be a permanent part of your lawn (typically, a poa "plant" only lasts for a year or two before dying). If you can break the life cycle of it reseeding itself, you'll have a good chance of eventually eliminating it from the lawn.

At Vander Giessen's, we've found a couple of very good pre-emergent (preventative) weed killers that are effective in prevention. Both Scotts Halts Crabgrass Preventer and Bonide Crabgrass & Weed Preventer are effective in prevention of poa (I know, they both have crabgrass in the name, but we're still talking poa!). Apply either of these granular products to your lawn in spring and fall to cover the cooler growing season.

A new product that Bonide has just introduced shows a lot of promise in preventing poa from growing, and it offers some help in killing young poa plants in your lawn. Bonide Crabgrass Plus is both a pre-emergent (meaning it kills weed seeds before they sprout) and post-emergent weed killer, but only for young plants. Keep in mind that this product will not kill larger, established areas of poa, but it will prevent it from spreading and kill recently-sprouted patches of poa. If you choose to use Crabgrass Plus, you don't need to use either of the others I've mentioned.

Next time you're ready to get advice on how to deal with the weeds in your lawn, be bold in asking for help, because now you know at least one of the weeds you're dealing with...and trust me, it's not crabgrass!