What Happens When You Mow Over Weeds?

Into each garden some weeds must come, sooner or later. After all, short of erecting an impermeable barrier over your lawn and garden, weed seeds will end up on your property, while other undesirables will spread in from the edges that you don’t control.

While early detection and action can help keep your lawn and garden weed-free, it’s a problem that is never going to disappear. Weed control and eradication is an ongoing task.

Does Mowing Weeds Kill Them?

While you may not see immediate results after mowing weeds, over time regular mowing can have a great impact on weeds in your yard. Even perennial weeds with strong root systems need to expend precious energy to regrow whenever they get chopped down by your mower. They need green foliage for photosynthesis to survive and thrive, and if those leaves and shoots keep getting cut off, the plants will eventually die.

Japanese knotweed

We had an issue in our yard with Japanese knotweed, planted by the previous owners. While we tried heavy mulch, and even applied a chemical weedkiller (always a last resort), what really worked was a few years of continual mowing. Without any foliage to transform sunlight to food, the root systems have died.

Annual weeds are even easier to kill through mowing, as they do not have deep root systems to draw upon. Once they’ve been cut back, they’re going to die.

Does Mowing Weeds Spread Them More?

Done properly, mowing weeds will not lead to them spreading around your yard. Cutting your lawn regularly before the weeds flower and set seed is important, but if you end up with weeds gone to seed, use a mower bag to stop any seeds from blowing around the property.

Either dispose of the lawn cuttings in a compost pile that will heat up enough to kill the seeds, or bag them for pick-up by the municipality.

Mow Weeds Before They Can Spread their Seeds

Mow Weeds Before They Can Spread their Seeds

Persistent lawn weeds such as dandelions produce lots of seeds that spread easily through the air. That’s why it’s important to cut them off before the seeds have a chance to take flight.

However, don’t cut them too fast, as the plants will be weakened the most when cut down just after they’ve bloomed, but before the seeds are ripe. That way, pollinators that need early spring blooms can feed off them, and then you can eliminate their further spread.

Is it Best Practice to Remove Weeds Before Mowing?

If you have a large lawn, removing weeds by hand may be an overwhelming task, unless you’ve maintained a thick, healthy turf with relatively few weeds. In a small patch, getting out a trowel and digging out weeds can be an effective way to eliminate weeds before they have a chance to spread. 

Removing the weeds before you mow is not always realistic, consider how many weeds there are and go from there. It may be better to just mow them and apply your treatment of choice, which I go over both options below in more detail.

What’s the Best Way to Remove Lawn Weeds Without Them Spreading?

1. Manually Removing Lawn Weeds

Manually Remove Weeds

If you decide to dig out weeds by hand, this is easier to do when the soil is wet, so either wait for a good rainfall to soak the ground, or run the sprinkler for a few hours prior to weeding.

Use a small, sharp trowel to dig down all around the root, and make sure you’re getting as much of the root system as possible, because many weeds will simply regrow from the roots. You can use a stand up weed puller tool to help with the process too. 

Gather up all the weeds and dispose of them in such a way that they can’t grow again.

Just throwing them in a heap at the back of your yard almost guarantees a new problem spot on your property, but you do have other options. If your municipality collects waste in green bins, throw them in there. If you want to compost them yourself, and you’re not sure that your compost will run hot enough to kill the weeds, consider boiling them first.

You can also pile the weeds separately, on a hard surface or tarp, and leave them to dry out thoroughly before adding them to your compost or burning the dry plant material. Just be sure you’re not burning poison oak or ivy, which can create dangerous fumes!

2. Organic Options

Green Gobbler 20% Vinegar Weed & Grass Killer | Natural & Organic | Concentrated | 1 Gallon Spray | Glyphosate Free Herbicide

If you don’t want to dig up all your weeds, try some environmentally-friendly methods to eliminate them from your lawn. A favorite natural cleaning solution for inside the house can also work wonders on your pesky weeds outside!

Horticultural vinegar is much stronger than ordinary culinary vinegar, with 20% acetic acid, as opposed to 5%. This makes it a powerful tool for killing weeds. Be sure that you’re applying it carefully, as it will also kill the grass you want to keep. However, a targeted spray on weeds can kill them in a matter of hours. Even the 5% solution will work if you add 1 oz of dish soap to a gallon of vinegar.

A great vinegar for killing weeds that I have used before is the Green Gobbler 20% Vinegar Weed Killer.

Flame weeders are another non-chemical option that can take care of your weed problem. Powered by butane or propane, a long wand allows you to walk upright and easily fry any weeds you come across.

3. Chemical Lawn Treatments

Chemical Lawn Treatments

Chemical fixes for eliminating weeds should always come after you’ve tried everything else, as they can have a detrimental effect on other living things and the environment in general.

Glyphosate-based weed killers such as Roundup should absolutely be your last resort. However, if your lawn is heavily infested with broad-leaf weeds, an application of a glyphosate weedkiller will target the weeds and leave your grass alone. 2,4-D is another weedkiller that will spare your grass but kill the weeds.

How Do You Prevent Lawn Weeds from Growing Again?

Obviously, it’s better to prevent weeds from taking root rather than having to get rid of them once they’ve turned up in your yard. If you work at making your lawn as thick and healthy as possible, you will have fewer weeds to worry about.

Start with regular feeding, to encourage, thick, lush growth. Don’t reach immediately for a chemical fertilizer; there are now many good organic lawn fertilizers on the market that will give your lawn the nutrients it needs without harming the environment. Aim to apply the fertilizer 3 or 4 times throughout the growing season.

You may think that cutting your grass short would discourage weeds, but you would be wrong! Setting your mower blades to 3.5 to 4 inches (9-10 cm) will keep weed seeds from sprouting. As a bonus, this longer grass is more resistant to grubs, so you have less need for pesticides.

If a bare patch develops in your lawn, don’t let it stay that way, or nature will move in and populate with weeds! Fill it in with sod, or sow it with grass seed as soon as possible.

Finally, keep your lawn well-watered for optimal healthy growth to crowd out weeds. Instead of daily light waterings, water it deeply 1 or 2 times a week for about 20 minutes, and only if there hasn’t been any rainfall to take care of it for you.

While some homeowners don’t mind the imperfections of a few weeds, they can get out of control and end up taking over. Mowing will often take care of any problems, as long as you catch the weeds before they set seed.

If nothing is working for you and you are just fed up with the constant weed maintenance, you can always try growing a ground cover that is designed to prevent weeds. Ground covers are growing rapidly as a lawn alternative and they require less overall maintenance, especially with weeds.  

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