Kill existing Lawn Weeds with a liquid post emergent herbicide that targets weeds, not your grass.
There are two main types of weeds that are commonly found in lawns. Broadleaf weeds, and Grassy weeds.
- Broadleaf weeds are more obvious. Their leaves aren’t grass like, instead they take on different shapes and textures that stand out in your grass. There are tons of broadleaf weeds but some of the most common are dandelion, clover, chickweed, plantain, and wild violet.
- Grassy weeds are a little harder to identify in your lawn since most of them are actual grasses, just not ones we wish to have in our lawns. These grassy weeds include crabgrass, nutsedge, poa annua, poa trivalis, and many more.
The best way to kill existing lawn weeds is with a liquid, lawn safe, post emergent herbicide. That sentence might scare you but it’s really simple. Spray lawn weeds with a liquid herbicide that will kill the weeds without killing your grass.
Liquid post emergent herbicides work so much better than granular post emergent herbicides.
Spot Treat Using Liquid Herbicide to Kill Lawn Weeds
Spot treating means going around your lawn with a liquid herbicide and spraying just the weeds. There are a lot of products that are safe to use on your lawn. A lot of these products even come with an applicator. The best products to use depend on whether you have cool season grass or warm season grass:
For Cool Season Grass:
There are several great products to choose from and sometimes you’ll want to change products depending on the weed you are trying to kill. But there are 2 products I recommend that will cover most weeds you’ll encounter in your cool season grass:
1. Ortho Weed B Gone Plus Crabgrass Control for spot treating lawn weeds. What’s great about this product is it’s ready to use (RTU) and doesn’t require any mixing. This is great it you have less weed pressure in your lawn or if you new to lawn care.
If you have a lot of weeds consider buying the concentrate here to save some money: Ortho Weed B Gone Concentrate. The concentrate is meant to be mixed with water in a tank sprayer, or hose end sprayer. Personally I’m not a fan of hose end sprayers since the mixing instructions can be confusing. I highly recommend a tank sprayer instead.
For tank sprayers you can either get a small 1-2 gallon tank or a larger 4 gallon tank. The 1-2 gallon tank is usually fine for spot treating: 1 Gallon Tank Sprayer
To treat your lawn, I recommend walking your lawn frequently (every week) and spraying any lawn weeds you see. This will help you stay on top of weeds and will prevent them from spreading. Many broadleaf weeds require a follow up treatment.
Also, it is highly recommend you mix a little Surfactant in with the Ortho Weed B gone, or any other liquid post emergent herbicide. The Surfactant helps the herbicide stick to the leaf of the plants. When broadleaf weeds are established they can get a waxy coating on their leaves that makes the herbicide hard to stick to. If you’ve ever been unsuccessful with liquid post emergent herbicides it’s likely this was the problem. Mixing in a little Surfactant can make a big difference. You can purchase Surfactant here: Surfactant
2. Another great post emergent liquid herbicide is Tenacity. The active ingredient in Tenacity is Mesotrione. Mesotrione kills a lot of tough grassy weeds that other herbicides don’t. Some of these include Creeping Bentgrass, Nimblewill, and can even knock back Poa Annua. These weeds can be a nuisance in cool season lawns and Tenacity is the best selective herbicide to kill them.
Another bonus of Tenacity is if you’re planning on seeding areas of your lawn or planning on a lawn renovation this is a safe product to use. Many other liquid herbicides recommend pausing applications at least a month before seeding. With Tenacity you can apply leading up to your renovation. You can even treat weeds at the same time as seeding (exception with fine fescue, and some other grass types, always read label).
Tenacity does have a couple of drawbacks. For starters it takes awhile to see results. It could take up to 2-3 weeks before weeds die back. Also, because it works by blocking photosynthesis in weeds, you’ll see the weeds turn a bleached white color. This will make weeds stand out as they are dying back. Lastly, you might see some temporary bleaching of your grass. This is usually temporary and grass will eventually green back up.
Mixing Surfactant with the Tenacity will help the herbicide stick to the weed.
For Warm Season Grass:
For warm season grass there are 2 liquid herbicides I recommend mainly because they treat a lot of different weeds and can also be used on several types of warm season grass. Unlike cool season grasses, warm season grasses can have different herbicide tolerances between species so always check labels.
1. For warm season lawns my favorite all around post emergent liquid herbicide is Image Southern Weed Killer. The label says for use on St. Augustine and Centipede grass but it can also be used on other warm season grasses such as Zoysia and Bermuda. This product is a concentrate and should be mixed with water in a concentrate. It will kill a lot of common weeds such as Dandelion, Clover, Chickweed, Dollarweed and many others.
2. The one downside to the Image Southern Lawn Weed Killer is it’s not the best choice for killing some of the tougher weeds such as Crabgrass, Doveweed, Dallisgrass, and others. If you have these weeds then I’d suggest using Celsius WG. You might have some sticker shock when you see the price of this product but keep in mind it is a concentrate that gets mixed with water so you get a lot of mileage out of it. Chances are this product will last you several seasons.
There is a cheaper option for Celsius WG which comes in a packet in granular form. This can be used to treat a smaller area. To treat your lawn with either of these products, I recommend walking your lawn frequently (every week) and spraying any lawn weeds you see. This will help you stay on top of weeds and will prevent them from spreading. Many broadleaf weeds require a follow up treatment. Both products benefit from adding a little Surfactant.
Blanket Spray If There’s a Lot of Lawn Weeds
What if you have so many weeds that spot treating isn’t an option?
If you have a lot of weeds mixed in with your lawn it might seem ridiculous to go around and spray each individual weed.
Instead, you’re better off blanket spraying your entire lawn with your lawn safe liquid herbicide. Blanket spraying usually requires a larger 4 gallon tank sprayer with a handle for pumping: 4 Gallon Tank Sprayer
You simply mix the liquid herbicide with water (according to the blanket application instructions on the label) and walk your entire lawn while spraying. I like to go up and down in rows, usually following my mowing lines.
Prevention with Pre-Emergent Herbicides
Prevention, using pre-emergent herbicides, is the best way to limit weed problems in your lawn. I strongly recommend using pre-emergent herbicides at 3 specific times during the year. Check out my custom lawn care program to see what pre-emergent to apply and when.
Pre-emergent herbicides prevent crabgrass, as well as other grassy, and broadleaf weeds from growing. Weed prevention is an important part of a solid lawn care program.
Chemical Free Ways to Kill Weeds in Lawn
There’s always the manual way, which is very effective if you don’t have that many weeds. There is a great weed grabbing tool that many people use to pull weeds completely out of their lawn, including the weeds root system.
It is especially effective for removing dandelions since dandelions have a long tap root that can be hard to rip out.
Renovate Lawn to Combat Weeds
If your lawn is overwhelmed with weeds you might be convinced you have to rip everything out and start over. Before doing so, consider core aerating and overseeding. Core aerating and overseeding, can drastically improve your lawn.
If you want to go a step further, top dressing your lawn, in addition to core aerating and overseeding is the ultimate lawn renovation.
As usual the best recommendation I can give for combating lawn weeds is sticking to a good lawn care program and maintaining a healthy lawn.
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