Amongst the DIY lawn care community, Crabgrass is the most notorious and difficult to manage “weeds” out there. This common grassy weed is invasive and undesirable. And without the proper prevention in controlling crabgrass, it can quickly kill the good ornamental grasses in your lawn (KBG, Tall Fescue, etc.) and takeover in a matter of no time
What is the lifecycle of Crabgrass?
Crabgrass seeds are shed from the plant ever year. These hearty seeds lay dormant in the soil over winter and begin to germinate when the soil temperatures reach optimal conditions. This is usually when the soil temps are consistently 55 degrees or warmer, for five consecutive days. In Massachusetts, this is usually in early April.
As crabgrass seeds emerge in the spring through early summer weeks, the plant can thrive through midsummer when left intended. Crabgrass can grow virtually anywhere and anytime and easily out compete the desired turf grasses (KBG, Ryegrass, TTTF, etc.). Which is why you can see crabgrass surviving through hot dry conditions, poor soil quality, and what appear to be impossible conditions like sidewalk cracks and edges of driveways.
How to control Crabgrass in cool season lawns?
- Apply Prodiamine 0-0-7 granular or Prodiamine 65 WDG as soil temperatures start to hit 50 degrees (early April)
- Use our Prodiamine Calculator for help with your exact liquid rates
- Apply Dimension granular or Dimension 2EW liquid 8 weeks later at the full bag rate (early June)
- Use our Dimension Calculator to calculate the exact liquid mix rates
- Spot treat crabgrass through the spring with post emergent crabgrass killer
By applying a split application of pre-emergent herbicides that target crabgrass weeds will be your best approach. The seeds will begin to germinate in the soil as soil temperatures hit 55 degrees Fahrenheit consistently for five consecutive days. This timing of course may be different in each lawn – factors such as the amount of sunlight/shade that a section of a lawn gets may be different than others. Grass alongside sidewalks, driveways and concrete patios will also be much warmer than the middle of the lawn, and much warmer than areas of the lawn that get mostly shade.
For well-established lawns and turf, apply a full application of Prodiamine as soil temperatures start to approach 50 degrees consistently. It is better to be too early than too late, so aiming for the first week of April (in Massachusetts for example).
Prodiamine specifically has great efficacy. This product is more effective for longer periods of time, and can sit in the soil longer than other active ingredients such as Dimension or Pendimethalin. Be sure to read the labels on Prodiamine, though, as there are more strict maximum annual application rates.
The second application should be Dimension. Prodiamine can be used, but Dimension is best here as it has post emergent qualities that can kill crabgrass and dandelions up to the the three leaf stage. As previously mentioned, Prodiamine has better efficacy, so it may affect your fall overseeding. If applied too heavily or too late could prevent your new (good) grass seeds from germinating in September
How To Kill crabgrass?
The best way of getting rid of crabgrass in your lawn is to first prevent them from emerging from the soil. However, sometimes (due to many factors) prevention isn’t good enough. Whether you moved into a new home and inherited a lot of crabgrass, or are reading this too late into the season and didn’t apply a pre-emergent, then a post emergent herbicide to kill crabgrass is in order.
One of the best active ingredients to kill crabgrass is quinclorac. When used as directed, quinclorac is a post emergent herbicide that can kill and control many broadleaf and grassy weeds in your lawn.
If you have more than just crabgrass in your lawn, then you may want to choose another post emergent herbicide that can kill more broadleaf and grassy weeds. These products will include active ingredients such as 2,4-D, and Dicamba.
One of my favorite all-in-one post emergent weed killers is Speedzone which also includes Mecoprop-P. You can also head to your local big box store or hardware store and find decent “over the counter” products with similar ingredients/ratios like Bayer Advanced All-In-One.
Lastly, you can take a non-chemical approach to controlling crabgrass. A simple hand weed tool like this can do just the trick to dig out those few pesky remaining crabgrass plants. Be sure to pierce deep enough into the soil to pull out the entire crabgrass, including the taproot.
In short, control crabgrass and prevent crabgrass with a good pre emergent herbicide schedule (split app). First Prodiamine (liquid or granular)followed by a full application of Dimension (liquid or granular). Next, stay on top of existing crabgrass by killing the crabgrass with a post emergent herbicide.
Please share a comment below if this crabgrass prevention works for you!
Frequently Asked Questions
The best time(s) to apply crabgrass pre-emergents such as Prodiamine or dimension for cool season lawns is in early spring and later spring. An application of Prodiamine in early April as soil temperatures approach 55 degrees, followed by a full application of Dimension 6-8 weeks later as soil temperatures approach 70 degrees. A split application of pre-emergents will be your best course of action in preventing crabgrass every year.