Crab grass and how to plant new grass seed

Asked July 26, 2016, 9:38 PM EDT

I plan to kill large patches of crabgrass with a spray.
How do I plant grass seed afterwards?
Do I simply sprinkle the seed over dead crabgrass? (Crabgrass too plentiful to dig up )

Hennepin County Minnesota

2 Responses

Crab grass is a problem for many with lawns and it has been answered by others. I have copied their advice. I would wait until next year and use a crabgrass preventer.
http://blog-yard-garden-news.extension.umn.edu/2015/04/spring-preemergent-applications-for.html
Crab grass is an annual grass weed. So the crab grass you see now will not come back next year, but the seeds it produces will! Crab grass will often be found in areas where your turf grass is thin, along sidewalks, in the shade, on paths etc. So if you can thicken up your turf grass that will help. You can overseed your lawn near the middle-end of August. This link has many resources to help you: http://www.extension.umn.edu/topics.html?topic=5&subtopic=155 and so will this one: http://www.extension.umn.edu/topics.html?topic=5&subtopic=155 If you over seed this fall that should help to thicken up your lawn. Then next spring, around the beginning of May, when the lilacs bloom in your yard or on your block or when soil temps reach 55 degrees you can apply a pre emergent weed killer/fertilizer. This product stops seeds from putting out roots (that is why you need to plant your grass seed in the fall for this process to work). It will last about 30-60 days and if you often see a bumper crop of crab grass in August you may need to apply it again near the end of July. You can also use a product called corn gluten meal as a pre emergent. The corn gluten meal (cgm) needs to be used 2x a year at the above times. You will also find that it takes about 3 years for it to 'build up' in the soil. So the kill percentage will increase each year- but because there is a residual in the soil it becomes harder to re seed your lawn. The cgm does have a small nitrogen component and will also fertlize your lawn. If you find that the crab grass is in one area you can use the pre emergent only on that area. If you have a lawn that has crab grass everywhere and perhaps your soil is a heavy clay, you may want to apply the pre emergent in 2 steps each time. The first time about 1 week earlier than you are 'supposed to' apply the product apply it to those areas that meet the warm concrete surfaces (along walks/driveways/streets) then a week later to the rest of your lawn. The seeds in the warmer areas will sprout about a week earlier so that is why you may want to divide the applications in this way. (I hope that makes sense). By thickening up your lawn (does it need to be aearated? do this 1 week before overseeding), and mowing your grass higher (about 3" during the summer) and watering irregularily but deeply you promote the grass and it shades out the weeds. Many weed seeds need light to germinate so by having a taller thicker lawn you shade the soil. I hope this is helpful to you. Good luck and thank you for asking the eXtension site your question. Have a great day

Crab grass is an annual weed (meaning it dies in the fall and comes back from seed in the spring). I am assuming you want to get rid of crab grass in your lawn. You can apply a pre-emergent to your lawn in the early spring to keep the seeds from germinating. If you miss applying the pre-emergent you can physically remove the crabgrass by digging it up or spot treat the crabgrass with a non-selective herbicide. An herbicide that is listed for broad leaved weeds will not kill crabgrass. Also, recently added to the retail market is crabgrass killer. Please follow all label instructions.

. Here are some other helpful websites:

OSUE FactSheets go to http://ohioline.osu.edu.

I reread your question and once the crab grass is dead take a garden rake and score the dirt so the grass seed in in contact with soil. Water frequently in summer every day is usually necessary for the most desirable results.