With Crabgrass showing now in full force, what can be done about it?
In Ontario, we have a new Cosmetic Pesticide Lawn. Post-emergent crabgrass control products like Acclaim are now longer approved.
If you have a lot of crabgrass problems, now is the time to consider how best to deal with this less-than-ideal grass.
First, recognize that the good thing about crabgrass is that it is an annual weed. When the first hard frost hits the lawns in the fall, crabgrass will die. It will be gone for the rest of the year. So at least we know that any crabgrass you may be seeing right now is only temporary.
The bad news about crabgrass, however, is that each crabgrass plant can produce thousands of seeds that can grow and infest your lawn next year. Anything we can do to reduce the amount of seed that is produced will make our job that much easier for next season.
When the crabgrass is still young, it will pull out fairly easily. Hand pulling is a great option as it gets rid of the crabgrass, hopefully before it has a chance to seed. Sometimes a small hand trowel or a dandelion weeder is helpful in getting the roots out. If you hand pull after a good rainfall, the roots will come up easier. Crabgrass, fortunately has fine fibrous roots rather than a long, tap root like a dandelion.
If the size of your crabgrass crop has exceeded your ability to hand pull in terms of quantity and size, one option is to use the permitted non-selective herbicides. These products contain either acetic acid (vinegar) or soap-based herbicides. Because they are non-selective, they will control not only your crabgrass; they will damage the desirable turfgrasses as well. So, one has to decide if damaging the good grasses is worth it.
If you have a large amount of crabgrass, it may be worth the risk of damaging the lawn in order to combat the crabgrass problem. Spray the crabgrass patch carefully. Try not to get any of the spray onto those areas of the lawn that do not have any crabgrass. Use a shield of cardboard or other material to protect those areas of the lawn that you do not want the spray to damage. Once the crabgrass (and the good grass) start to yellow, spread some black soil on the damaged areas and spread some high quality grass seed. Keep the seed constantly moist by watering at least twice a day. As the new grass seed germinates it will help to fill in the spaces left by the crabgrass. The black soil, while it does look like a band aid solution on your lawn, at least shows that you are doing something about the crabgrass.
Later, as the crabgrass starts to go to seed, do your best to remove as much of the seed heads as possible. As the crabgrass matures, it will start to spread out on the ground, lying flat and close to the surface. Sometimes you may be able to use a stiff rake to pull some plant out.
Another way to help reduce seed production is to rake the prostrate seed heads before mowing. That way they will be upright and vertical enough to be mowed off. Bag the seed head clippings and dispose of the seed.
As we get into the fall, continue seeding as needed so that the areas where the crabgrass problems occurred are growing in nice and thick. Add fertilizer to also help with the thickening and turf density. Crabgrass will die off with a hard frost and will certainly be gone by winter.
Once the new season begins, plan to tackle the crabgrass by applying a corn gluten meal fertilizer in late April through early May. Corn gluten meal acts as a natural fertilizer as well as a crabgrass preventer. There is a protein in corn gluten meal that disrupts the normal root development of germinating seedlings. Without a proper root, those seedlings will die from a lack of moisture. Corn gluten meal is active for about 4 weeks, so timing of the application is critical. About 20 lb. of corn gluten meal need to be applied to 1,000 sq ft of lawn. Remember that it is also a fertilizer, so do not apply another fertilizer at the same time.
Care of your lawn to reduce crabgrass.
Once you start mowing your lawn, make sure to set your mowing height to 3 inches so that there will be more leaf blade height to shade the ground. Compared to a mowing height of say 2 inches, the 3 inch height provides an extra inch of leaf blade. That may not seem like much, but it is 50% more leaf blade. That extra shade it provides helps to reduce crabgrass germination.
Crabgrass likes to grow in warm, sunny spots. That's why you often find it along the edge of the driveway where the concrete or asphalt transfers its heat to the lawn adjacent to it. Crabgrass loves that warmer soil. By mowing your lawn at 3 inches, the extra shade will keep the ground cooler and moister. Lower soil temperatures will help to increase the lawn density and the lawn's vigour. All of these factors will reduce the amount of crabgrass that will infest your lawn.
The higher mowing height also helps to reduce weed germination so that less weed control will be required. As well, cooler soil temperatures will help to reduce chinch bug populations and chinch bug damage, so your lawn care all around is much easier.