You’ll find crabgrass in lawns, landscapes, vegetable gardens, orchards, vineyards, and many other home and agricultural areas. Crabgrass has other names including crowfoot grass, watergrass, and summer grass. It grows in most parts of the United States. Crabgrass seeds can germinate each year when soil temperatures reach over 55 degrees for 5 days. This “wakes up” all grass seed including crabgrass, and starts it on its process of growing. Effective control begins with a preemergent crabgrass preventer. Crabgrass must be stopped before the seed germinates.
When temperatures start to warm in the spring, the crabgrass seed “can” germinate at that point. Does not mean it will. If colder temperatures prevail, it will still take a while to germinate. Crabgrass is easy to manage using a variety of natural and chemical controls. Controlling and preventing crabgrass is important, because the seeds can remain viable for at least 3 years in soil.
So how can you tell when is the best time to apply a pre emergent crabgrass preventer?
When to Apply: There are guidelines to applying any crabgrass preventer.
- Remember “55 and 5” 55 degrees for 5 days in a row and its time to apply!
- Use your local soil temperature map
- Most states with cool season grasses should apply in early spring from early March to early May. This is usually the time that Forsythia blooms. Forsythia is usually the first flowering shrub that blooms in the spring. To be most effective, Crabgrass Preventer must be applied before forsythia is in full bloom.
- If you live in a southern state, follow our Southern Lawn Care Tips
- You must apply before the period of active growth begins
Periods of Active Crabgrass Growth
Grass Type Period of active growth
Cool Season Grasses
- Bentgrass March–June
- Bluegrass late February-early April
- Fescue early March–June
- Ryegrass late February–June
Warm Season Grasses
- Bermudagrass April–late September
- Dichondra April–October
- Kikuyugrass February–November
- St. Augustinegrass March–October
- Zoysiagrass April–October
This could mean an early March application in California or Florida, but late April in Ohio or New York.
- Apply crabgrass preventer in early spring to prevent crabgrass seeds from germinating.
- If you are planning to seed your lawn in the spring, do not use crabgrass preventer since it will not only prevent crabgrass seeds from sprouting, but also stop all grass seed from growing.
- Regular feedings, 2-4 times per year, provide the nutrients your lawn needs to grow thick to help crowd out crabgrass. Use Scotts Turfbuilder or Sta Green Weed and Feed products.
- Mowing at a height best for your lawn allows the grass to grow thick to help prevent crabgrass seeds from germinating by blocking sunlight’s access to the soil.
The key to crabgrass control is making sure the seeds cannot germinate. The most likely places to find crabgrass are sunny areas with low cut grass, heavy traffic areas or along the driveway or sidewalk. Crabgrass also is seen in flower and vegetable gardens where soil has been tilled or raked.
Apply the product when the ground temperature rises above 55 degrees. Since it’s difficult for most of us to know the soil temperature, use the 55 and 5 guideline. When you notice forsythia, shrubs blooming and trees budding, it’s time to apply the herbicide. Warm nights and periods of rainfall encourage crabgrass germination. If your weather fits this pattern, get the herbicide in place right away.
Crabgrass Prevention and Control : What works and how to apply.
Your main objective is to “prevent” crabgrass. That is sometimes easier said than done! Your other option is “controlling” crabgrass. It’s a lot of work either way, but can be done.
- Prevention is early application
- Control is during the season
Prevention: The two leading brands of crabgrass preventers are Scotts Halts and Sta Green Crab Ex.
- Scotts Halts active ingredient is Pendimethalin. Read the fact sheet here
- Sta Green Crab Ex active ingredient is Prodiamine. Read the fact sheet here
Control: You can control active crabgrass and other weeds through out the season with weed and feed products. You can use a weed and feed granule product, liquid or a weed only product like Ortho Weed B Gon.
Weed and Feed Products: During the season, you can help control weeds by using a weed and feed product to help build strong roots and thicker lawns. The two herbicides most commonly used in fertilizer and herbicide weed-and-feed formulas are the selective herbicides Trimec and Atrazine.
Trimec is a selective, contact, systemic herbicide that is a combination of three chemicals: 2, 4-D, dicambra and mecoprop, all of which are damaging to warm season grass. This chemical is commonly found in weed and feed products for cool season grasses. Applied to a wet lawn, the granules of Trimec stick to the wet weeds and effectively kill them.
Atrazine, commonly used in weed and feed formulas for warm season grasses like St. Augustine, is a selective herbicide that kills systemically through interruption of photosynthesis. The weeds absord the atrazine through its roots. That stops the weeds ability to absord energy from the sun and they die. Any atrazine based product needs to be applied to a dry lawn. When weeds are present, spread the granular compound on dry grass and water in and make a maximum of two applications each year.
Cautions/Instructions: All crabgrass products and weed and feed products contain dangerous chemicals. Read the label carefully for the the brand you have selected. Always apply the product according to the directions on the label. Remember, pre emergent products like Scotts Halts and Sta Green Crab Ex, will also kill germinating grass seeds.
What to do with any remaining product? Any left over granular or liquid product should be good to use for up to a year. Just keep it dry and of course keep liquids from freezing. If you don’t want that bag of crabgrass killer sitting in the garage all summer, you can still use it during the season. It still contains fertilizer that will help your lawn, but will not do anything for crabgrass during the growing season. I usually have at least a half a bag left and just mix it in with my summer to fall lawn feedings. This way it gets used up and its one less piece of clutter in the garage.
By Victoria Stone