new lawn/crabgrass

Asked September 27, 2017, 3:00 PM EDT

We built a new house, put in sprinkler system etc- End of June we had it hydroseeded. It hasn't really come in very good- landscaper and seed guy came out and looked at it and said it was "stunted" because we had a hot spell beginning of July. Anyway- now we have tons of crabgrass.... I spoke with a different landscaper because I wasn't confident in other. He came out and looked- said the crabgrass was a problem and other guy should have killed it all and put a pre-emergent down.. at any rate he said we could kill everything with round up, put down a pre-emergent and then seed this fall for growth next Spring. OR- we could spot kill with Round Up, put down a pre-emergent and seed and see how it looks next summer. I am getting pretty frustrated with so many different options/opinions and have already spent so much money on it...but I'm tired of messing around and having it look awful even after spending so much money on it. I just want it done and done right. What is your recommendation?


Thank you. Kari Score

Cass County North Dakota

7 Responses

Hi Kari,

Are you sure the problem is crabgrass and not quackgrass? They are two very different weedy grasses. Crabgrass is an annual weed meaning that it will be killed by winter temperatures. It does reseed so you would need to apply a pre-emergent crabgrass preventer in spring (usually late April or early May) to prevent crabgrass seed from germinating next year.

Quackgrass is a perennial weed meaning that it will survive winter and come back next year. Unfortunately, there is no selective herbicide that will kill quackgrass without killing the desirable lawn grass.

Your next question is probably going to be: how do I tell the difference between the two weedy grasses? Quackgrass has extensive rhizomes. This means that when you try and pull the weed out of the ground, you will not be able to pull out the root system. Crabgrass lacks rhizomes so you should be able to pull the whole plant including the roots out of the ground.

If it turns out that you have crabgrass, then your strategy will be to put down a crabgrass pre-emergent herbicide in the spring. If you have quackgrass, you can kill that section of lawn with Roundup or any product that contains the active ingredient glyphosate. Considering how late it is in the season, you can try and dormant seed in early November. In other words, you would apply the seed after the weather has turned cold. The seed would lay dormant under the snow and then germinate in the spring after the snow melts. This is a decent option but so is spring seeding.

If you do decide to reseed in spring, be careful about the use of pre-emergent herbicides. Some common pre-emergent herbicides will actually prevent your grass seed from germinating as well as the weed seeds. Siduron/Tupersan is usually ok if you are seeding new grass.

This is complicated stuff! If you have any follow-up questions, I would be happy to answer them.

I believe it is quackgrass. What I am wondering- we had a landscaper spray and prep our yard before he did the Hydro-Seed. Is this something he should have dealt with? It is a new developement- new construction. We spent a lot of money already- and if this is something that he should have dealt with before the hydro-seeding, I will want to contact him and discuss the issue. But if it's "just one of those things" I will deal with it. On a side note- I recall last summer at least 2 other yards in the neighborhood that had been seeded, and then completely sprayed with Round Up (killed) and re-seeded... Thanks, Kari Score

My (new) landscaper says it crabgrass- he wants to spot spray round up on every plant- but from and then overseed this fall.Is this ok to do? And then do a preemergent in the Spring? Is the Round UP even necessary this Fall? Since it's already October and we will do a pre-emergent in the Spring? Help! I'm a bit confused. Kari Score

I am replying to both responses that you have sent. Your first question: should your hydro seed company be responsible for the proliferation of weedy grasses? I can't answer that question. It really depends on your contract with him. I do know that there are no good pre-emergent herbicides that you can put down at the time of seeding. These pre-emergent herbicides would have stopped your turf grass from germinating. However, it doesn't hurt to discuss the matter with the company.

Your new landscaper says the problem is crabgrass. If it is, then remember that crabgrass will die this winter because it is an annual. Spraying crabgrass is a waste at this time of year.

However, if the grass is quackgrass, then Roundup would be necessary to kill it. Quackgrass is a perennial.

Yes, you can overseed this fall but it is getting late in the season to do so. The later you seed this fall, the greater the risk the grass won't survive winter.

If you do overseed this fall, then yes you can put down a pre-emergent herbicide for crabgrass in the spring. That is one reason to overseed in the fall.

Good luck!


I did have one other thought. Maybe your new landscaper is suggesting a Roundup application to the crabgrass as a means of opening up space to overseed. Roundup will kill the crabgrass but will take 7-10 days to do it.

Thank you! Your response is very helpful! Just spoke with the new landscaper- he talked to an agronomist and said he found something that will work on the crabgrass this Fall, then he will wait 7-10 days and then overseed this Fall. Then in the spring we will apply the pre-emergent. Thank you. Kari Score