Q & A with Weed Man: When is the best time to put a pre-emergent on my lawn?

Q: When is the best time to put a pre-emergent on my lawn?

A: Great question! For those of us in the North, it’s pretty hard to see our lawns with all of this white stuff still hanging around. For those in the South and Mid-West, it’s time to start thinking about getting a pre-emergent application out there on the turf.

Weed Man always gets a lot questions around this time of the year regarding when to apply a pre-emergent and prevent crabgrass from taking over a lawn. To tell you the truth, there is no easy answer. There are multiple factors to consider before deciding on the proper time, some of which I’ll address below.

The first thing you will need to look at is what type of product you are applying. If you are utilizing a product that contains Prodiamine, then you will have to be quick to the punch, as it is a preventative treatment. This means that it stops weedy grasses like crabgrass from germinating, and therefore must be applied before germination begins. If you opt for a product with the active ingredient Dithiopyr, on the other hand, then you can be a little more flexible with your time. It can go down a bit later and still get control of crabgrass even if it has already started to germinate.

One other thing to keep in mind is that the germination of crabgrass can vary. It can start germinating in a sunny location, typically a full month ahead of other parts of the lawn that may be more shaded. A good way to know when crabgrass is about to germinate is to use an indicator plant, such as the forsythia bush. Once the forsythia bush starts to flower, it is likely that crabgrass could be starting to germinate. However, in my opinion, the best way to tell is by monitoring farmers in the fields planting corn crops. Corn planting is a good indicator that soil temperatures are right, and you can bet that crabgrass will take advantage of these ideal conditions and start germinating.

Pre-emergents that are applied too early may not last long enough throughout the season, and you may have breakthrough in the middle of the summer. Believe me when I say that trying to control crabgrass in the heat of summer is a BIG challenge. Also, a wetter than average spring can affect the longevity of a pre-emergent, causing it to break down faster than usual. Again, this allows for possible crabgrass breakthrough. Last year we witnessed this occurring in most of the country, which resulted in numerous crabgrass issues once July and August arrived.

Last but not least – crabgrass is typically worse along the edges of driveways and sidewalks, so paying special attention to those areas is really important. This undesirable lawn invader is also more prevalent when the turf is thin or weak. Keeping your lawn thick and healthy will result in fewer opportunities for crabgrass to germinate. When applying the application, ensure that you don’t miss any areas of the lawn, otherwise you will have crabgrass breakthrough as you can see in the picture below:


Lots of things to remember, but reading the label and following the directions provided will help you prevent crabgrass from germinating later in the summer. Weed Man can also help if you have any questions when it comes to crabgrass control and pre-emergent applications. To find the location nearest to you, please visit our locator map by clicking HERE.

Looking forward to a great spring ahead,


Weed Man USA


1 thought on “Q & A with Weed Man: When is the best time to put a pre-emergent on my lawn?

  1. Great tips, in the case of a wet spring I think we might have the same cup of tea this year, looking at all the snow still out there. What are your thought on that?

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