If it feels like crabgrass has suddenly exploded this year, you’re not imagining it.
Minnesota and Wisconsin have experienced one of the hottest stretches on record, with 10 consecutive days of temperatures in the 90s. While this weather has been hard on our cool season lawns, it has been almost perfect for crabgrass.
Over the past few weeks, we’ve received a significant increase in calls from homeowners asking why their lawn suddenly has bright green patches growing much faster than everything else.
The answer is simple. Your lawn is struggling with the heat. The crabgrass isn’t.
Why Crabgrass Loves Hot Weather
Most lawns in Minnesota and Wisconsin are made up of cool season grasses such as Kentucky bluegrass, perennial ryegrass, and fine fescue.
These grasses grow best when temperatures are between 60 and 75 degrees. When temperatures climb into the upper 80s and 90s for extended periods, they begin to conserve energy. Growth slows dramatically, color fades, and in severe cases they may even go dormant until cooler weather returns.
Crabgrass behaves completely differently.
It is a warm season annual grass that thrives during hot weather. As your desirable grass slows down, crabgrass accelerates. It grows quickly, stays bright green, and often becomes the tallest plant in the lawn within just a few days after mowing.
That contrast makes crabgrass much more noticeable than it would be during a typical Minnesota summer.
How to Identify Crabgrass
Crabgrass is fairly easy to recognize once you know what to look for. Common characteristics include:
- Bright lime green color compared to the surrounding lawn
- Rapid growth between mowings
- Wider leaf blades than Kentucky bluegrass
- Clumps that spread outward from a central point
- Most noticeable during July, August, and early September
Why Is It Showing Up Now?
The combination of prolonged heat and stressed turf has created ideal growing conditions for crabgrass.
Areas next to driveways, sidewalks, streets, and patios are especially vulnerable because pavement absorbs and radiates heat back into the lawn. Those areas often become significantly hotter than the rest of the yard.
As the desirable grass weakens from the extra heat, crabgrass takes advantage of the opening.
We’re generally see two different situations with crabgrass during the summer.
Situation 1: Crabgrass Along Driveways, Sidewalks, and Roads or Small Patches
This lawn has crabgrass along the curb edge. This is an example of situation 1.
This is by far the most common situation. Small patches appear where the lawn borders paved surfaces. The extra heat weakens the cool season grass while encouraging rapid crabgrass growth.
Fortunately, this is usually the easier situation to correct. If you notice these patches, simply let us know. We can spot treat those areas with a post emergent herbicide.
One thing to keep in mind is that crabgrass is more resilient during periods of extreme heat. It may require more than one treatment to achieve complete control. If you still see surviving plants after treatment, just contact us again and we will retreat those areas.
Once cooler weather returns, your desirable grass will begin growing again and can naturally fill many of the spaces left behind.
Situation 2: Crabgrass Throughout the Lawn
The right lawn has more widespread crabgrass. This visually shows situation 2.
Sometimes crabgrass isn’t limited to a few patches. Instead, it has spread throughout much of the lawn. When this happens, homeowners have a decision to make.
We can absolutely treat the crabgrass. However, it’s important to understand what that will look like afterward.
If a large portion of the green color you’re seeing is actually crabgrass, treating it means removing much of that green color. The lawn may temporarily appear much browner because the crabgrass has been eliminated while the desirable grass is still stressed by the summer heat.
For that reason, many homeowners choose not to treat widespread crabgrass during the hottest part of the summer. They would rather keep some green color in the lawn until cooler temperatures return.
There isn’t a right or wrong answer. It depends on your expectations and how you want your lawn to look over the next several weeks.
Regardless of which option you choose, we strongly recommend fall seeding. Fall is the best time to establish cool season grasses in Minnesota and Wisconsin. A thicker lawn leaves fewer open spaces where crabgrass can establish next year.
“I Had a Crabgrass Preventer. Why Do I Have Crabgrass?”
This is one of the most common questions we receive when crabgrass occurs in hot weather conditions. Crabgrass pre emergent herbicides are an excellent tool, but they are not perfect.
These products create a barrier near the soil surface that prevents newly germinating crabgrass seedlings from becoming established. In most years, they provide excellent control. However, no pre emergent herbicide provides 100 percent control.
Years with prolonged heat, can lead to higher soil temperatures. Higher soil temperatures can cause pre emergent barriers to break down more quickly than they would during a typical Minnesota and Wisconsin spring and summer thus reducing their overall effectiveness.
This means that while most crabgrass may be prevented, some plants can still emerge. That is why post emergent spot treatments are sometimes necessary, even when a pre emergent application was made earlier in the year.
The combination of a spring pre emergent followed by post treatments when necessary provides the best long term control.
Crabgrass after treatment
“If I Don’t Treat It, Will I Have Crabgrass Forever?”
Fortunately, no. Crabgrass is an annual plant. Every crabgrass plant growing in your lawn today will die after the first hard frosts this fall, regardless of whether it is treated. The plant itself does not survive the winter.
Even if your lawn has almost no crabgrass today, it almost certainly contains crabgrass seed. Birds, mowing equipment, shoes, pets, wind, and soil movement continually introduce new seed into lawns every year.
The goal isn’t to eliminate every seed. That simply isn’t possible. The goal is to grow a dense, healthy lawn that prevents those seeds from successfully becoming established.
What You Can Do Right Now
If you have just a few patches of crabgrass, let us know so we can spot treat them.
If crabgrass is widespread throughout the lawn, decide whether you prefer treating it now or waiting until fall. Both are reasonable options depending on your expectations.
Also continue good maintenance practices. Continue watering deeply to reduce heat stress on your cool season grass. Avoid mowing during the hottest part of the day whenever possible.
Plan for fall overseeding if your lawn has become thin. This is one of the best investments you can make to reduce crabgrass pressure in future years.
How bioLawn Can Help
Our agronomy team can help determine whether what you’re seeing is actually crabgrass or another grassy weed.
If the infestation is limited, we can provide targeted post emergent treatments to control it.
If crabgrass is widespread, we’ll help you determine whether treatment now or renovation this fall makes the most sense for your lawn.
Finally, we’ll work with you this fall to strengthen your lawn through overseeding and continue protecting it next spring with a crabgrass pre emergent application.
No lawn is completely free of crabgrass seed. The difference between a lawn with very little crabgrass and one with a lot of crabgrass is usually the health and density of the desirable grass.
By combining spring prevention, summer monitoring, and fall lawn improvement, we can greatly reduce crabgrass pressure and help your lawn stay healthier year after year.