Carpetgrass is like Jekyll and Hyde. If you’re dealing with its dark side, this guide gives you several options to get rid of carpetgrass as a weed so you can vanquish the villain from your yard for good.
To learn more about the Hyde side — what makes carpetgrass a good choice for some lawns — see our article about carpetgrass as a turfgrass.
- 9 Ways to Get Rid of Carpetgrass
- How to Prevent Carpetgrass
- How to Identify Carpetgrass
- FAQ About Carpetgrass
- How to Keep Your Lawn Healthy and Weed-Free
9 Ways to Get Rid of Carpetgrass
One thing that makes carpetgrass so annoying for homeowners is that it’s perennial. Perennial weeds don’t die in winter. They go dormant and come back again to haunt you the next year … and the next year … and the next year. Basically, perennial weeds like carpetgrass will never go away unless you kill them, roots and all.
Try these methods to kill the carpetgrass in your lawn sooner rather than later.
1. Parch the Carpetgrass
Carpetgrass loves moist soil. Without moisture, it will eventually die of natural causes. So, one of the easiest ways to get rid of carpetgrass is to stop watering it. Wherever you see carpetgrass in your yard, don’t water that spot until the weeds die and turn brown. Once they’re dead, remove them from the lawn with a rake.
This method is simple, but it can be problematic. For one thing, you can’t control the rain. If Mother Nature provides enough moisture for the carpetgrass, it won’t die just because you stopped watering it.
Another issue is that when you deprive the carpetgrass of water, you’re also depriving your actual lawn grass. Parching the carpetgrass is only a viable solution if you have a drought-tolerant grass type such as Bermudagrass, St. Augustinegrass, or Zoysiagrass.
2. Fertilize Your Soil (To Kill the Carpetgrass)
Counterintuitive though it may seem, carpetgrass thrives on low-fertility soils, or, in other words, soils lacking in essential plant nutrients. What does this mean? Adding those nutrients to your soil in the form of fertilizer or another soil amendment may be enough to kill carpetgrass. Fertilizer also helps your lawn grow thicker, so it can crowd out all kinds of weeds.
Before adding anything to your soil, get a professional soil test from a lab online or from your local university extension program. The soil test will tell you which nutrients (such as nitrogen, phosphorus, and potassium) your soil is missing. From there, you can choose the right nutrient supplements.
3. Raise Your Soil’s pH
Your soil test results will also tell you your soil’s pH level. An acidic pH of 5 – 6 is the ideal range for carpetgrass. If you make your soil more alkaline by raising the pH to about 7.5, your yard will become inhospitable for the weed, and carpetgrass will eventually die out.
Raising soil pH sounds complicated and scientific, but it’s actually pretty easy. All you need to do is work a soil amendment called agricultural lime into your topsoil. You can purchase agricultural lime (sometimes called “gardening lime” or just “lime”) at most garden supply centers or online. A rate of 2 pounds of lime per 1,000 square feet should do the trick to get rid of carpetgrass.
4. Water with Saltwater
Carpetgrass can’t survive with an excess of salt in the soil. Watering with saltwater is an easy way to make your soil saltier.
First, mix 2 cups of table salt into 7 – 10 gallons of water and wait for the salt to dissolve completely (which may take a while). Once the mixture is complete, put some of the saltwater in a watering can and douse the spots in your lawn where carpetgrass has taken over. Water when there’s no rain in the forecast for at least three days because rain could wash the salt away.
WARNING: Excess salt in the soil may harm your lawn grass if you don’t have a salt-tolerant grass type, such as Zoysiagrass or St. Augustinegrass. Salt is bad for many plants, too, so be careful not to get any of the saltwater on sensitive flowers or other landscape plants.
5. Douse with Vinegar (Carefully)
Vinegar is one of the most common alternatives to chemical herbicides, and it kills pretty much any weed, including carpetgrass. Simply douse any patches of carpetgrass with undiluted white vinegar to kill them.
WARNING: Vinegar kills all plants, not just weeds. DO NOT pour vinegar on your lawn or other plants you want to keep alive. Vinegar is mostly for carpetgrass in isolated areas, like the cracks in your driveway.
6. Apply Arm & Hammer Powder Laundry Detergent
Arm & Hammer powder laundry detergent (available just about anywhere) kills carpetgrass weeds without harming your lawn grass or other plants. Mix 2 scoops of Arm & Hammer powder with a gallon of water. It will form a paste-like consistency. Pour this mixture over the carpetgrass to kill it.
WARNING: Be careful where you apply Arm & Hammer. If pets or small children eat the grass after you treat it, they may get sick.
7. Sprinkle Baking Soda
Baking soda is another household item that can kill carpetgrass. For this method, wet the carpetgrass first with a hose, watering can, or sprinkler. You want the soil to be sufficiently wet, but not soaking. Then, sprinkle a good helping of baking soda over the weeds.
WARNING: Baking soda may cause stress to your grass and other plants, but it likely won’t kill them outright. Of course, that depends on how sensitive your grass type and plants are, so use caution.
8. Scatter Borax over Carpetgrass
Borax, sometimes called sodium borate, is a powder form of boric acid. It can kill carpetgrass without harming most other types of grass. Take a handful of the powder and scatter it over the carpetgrass like fertilizer. After about 10 days, the weeds should be dead or nearly dead, and you should be able to rake them out of your lawn easily.
Carpetgrass may grow back after one borax application, but it should be weaker and thinner. Keep applying borax every 6 – 8 weeks or so, and the carpetgrass will get weaker and weaker each time it comes back, until eventually it stays gone for good.
9. Get Tough with Chemical Herbicides
When gentler and more eco-friendly methods fail, you can resort to the most potent form of weed control: chemical herbicides. Look for a post-emergent herbicide that works on grassy weeds.
Herbicides that kill carpetgrass include:
Always check the product label before purchasing a herbicide to see if carpetgrass is on the list of weeds controlled. Also, note that some chemicals may require a license for use in some states.
For application instructions and how often to apply the herbicide, see the label on the specific product you buy. Each product is a little different.
Note: Pre-emergent herbicides can prevent weeds but won’t do anything to carpetgrass that’s already there. And some herbicides are made to kill broadleaf weeds only, not grassy weeds.
How to Prevent Carpetgrass
The best way to keep carpetgrass out of your yard in the first place is to maintain your lawn so that it grows thick and healthy. Dense lawns crowd out weeds on their own.
To keep your lawn healthy so it resists the invasion of carpetgrass:
- Don’t over-water. Only water when your grass shows signs of drought stress, such as fading color or leaf curling. Watering too frequently leads to overly moist soil, which leads to carpetgrass.
- Mow to the right height for your grass type. Each type of grass has specific mowing requirements to keep it as healthy and thick as possible. Know your grass type and adjust your mower height accordingly.
- Fertilize your grass on the right schedule. Research your grass type to find out how many fertilizer applications it needs each year to grow its best. In general, you should fertilize at least three times per year.
- Improve soil drainage. If your soil has poor drainage, your lawn’s roots will become weak, which will lead to weaker grass in general. Plus, poor drainage means wet soil, which is a breeding ground for carpetgrass. You can improve soil drainage by aerating the lawn or adding soil amendments such as compost.
Prevent carpetgrass in flower beds and gardens by spreading mulch. Mulch blocks weeds from growing and has many other benefits for your plants.
If you’ve had problems with carpetgrass in the past, you may also want to apply a pre-emergent herbicide just to be safe. Pre-emergent herbicides prevent weeds from ever sprouting. Again, look for pre-emergents labeled for use on carpetgrass. For them to be effective, you have to apply pre-emergents in the early spring before carpetgrass’s growing season.
How to Identify Carpetgrass
Many grassy weeds look similar. Make sure carpetgrass is the one in your lawn before treating it. Methods that work for one grassy weed don’t necessarily work for all of them.
There are two types of carpetgrass, and they look a little different from each other.
Narrowleaf carpetgrass (Axonopus affinis or Axonopus fissifolius) has thinner leaf blades and is pale green in color.
Broadleaf carpetgrass (Axonopus compressus) — not to be confused with broadleaf weeds in general, as this is still a grassy weed — has wider leaves that are darker green and shiny.
These are some identifying features of both types of carpetgrass that you can use to tell them apart from other grassy weeds:
- Grows in a carpet-like mat (hence, the name)
- Spreads aggressively
- Produces seed stalks in summer; seed stalks can reach up to 12 inches tall and have Y-shaped seed heads at the top, sometimes with a third seed head just below the “Y”
- Grass blade tips are “boat-shaped”
- Open/split grass sheath with hairs along the edge (see this illustration of what a grass sheath is and what the different types look like)
Check North Carolina State University’s Carpetgrass page for detailed descriptions and photos of each individual part of carpetgrass.
FAQ About Carpetgrass
Poor soil conditions and wet environments are the most common causes of carpetgrass.
Other common names for carpetgrass include flatgrass, Louisianagrass, and petit gazon. If you see any of these names on a product label, they mean carpetgrass.
Carpetgrass and centipedegrass look similar and both spread by above-ground stems called stolons, so they’re often confused for each other. In fact, if you have centipedegrass, you might not even realize carpetgrass has encroached on your lawn until the seed stalks shoot up in the summer months. Carpetgrass seeds are even included in some centipede seed mixes.
Aside from the seed stalks, you may be able to tell the difference because centipedegrass has little hairs along the edges of its leaf blades, while carpetgrass doesn’t.
Crabgrass is another common grassy weed that looks like carpetgrass and produces similar seed stalks in summer.
Some features of crabgrass that can help you tell it apart from carpetgrass:
Star pattern: As it sprouts, crabgrass stems grow outward from the center of the plant in a star-like pattern.
Earlier sprouting: Crabgrass is one of the first weeds to sprout in spring, while carpetgrass doesn’t usually appear until later in the season when temperatures are warmer.
Color: Crabgrass can vary in color from medium to dark green and sometimes has purplish streaks along its stems.
Carpetweed is a summer annual weed with small white flowers, and it isn’t related to carpetgrass except that their names are similar. If you see carpetweed on a product label, it doesn’t mean carpetgrass.
How to Keep Your Lawn Healthy and Weed-Free
The best defense against any weed — carpetgrass included — is proper lawn care. Learn the best schedule for watering, mowing, and fertilizing your grass type, and stick to it. Your grass will be more attractive in general in addition to having fewer weeds.
Mowing the lawn at least every two weeks (preferably every week) is one of the most important things you can do for your grass, but it’s also one of the most time-consuming. When you don’t have time to mow your grass, LawnStarter’s local lawn care pros can take care of it for you, so you can have a healthy, weed-free lawn without all the work that goes into it.
Main Photo Credit: Harry Rose / Flickr / CC BY 2.0