Can You Compost Weeds?

weeds in a homemade compost area

If you’ve ever wondered if you can compost weeds, the answer is yes – but with restrictions. You have to consider the kinds of weeds, whether they have seeds, pests, diseases, and your local regulations.

Is it possible to compost weeds?

close-up of smooth crabgrass (Digitaria ischaemum)
F. D. Richards | Flickr | CC BY-SA 2.0

You can compost weeds as long as you familiarize yourself with the process and have the right conditions.

Although weeds compete with grass or plants, can be difficult to eliminate, harbor pests and diseases, and ruin curb appeal, they can also benefit your soil, plants, and the environment: 

  • Nutrient boost: Puts macronutrients such as nitrogen, phosphorus, and potassium back into the soil, helping future plants grow healthy and reducing the need for synthetic fertilizers.
  • Less landfill waste: Keeps waste out of landfills, reducing harmful emissions and contributing to a sustainable waste management system. By doing it on site, you help maintain a closed-loop system where garden waste is reused within the garden.
  • Better soil health: Improves soil structure, promotes better water retention, and helps with root development. It also adds organic matter that supports microbial activity beneficial for soil health.
  • Lower maintenance cost: Eliminates the need to pay for weed removal and disposal. As you produce your own compost, you also save money that you would otherwise spend on commercial compost or soil amendments.
  • Environmental benefits: You need fewer pre-emergent and post-emergent herbicides for weed control, which is better for the environment and local ecosystems. Anytime you compost organic matter, you help reduce carbon emissions and mitigate climate change.

When can you compost weeds?

Woman hand clearing, pulling out some weed form her garden, using garden equipment
Khaligo | Adobe Stock Free | License

You can compost weeds under the following conditions:

If the weeds are annuals

Annual weeds, which only live for one year, are easier to compost because they don’t have deep roots. Perennial weeds, however, can regrow from roots or rhizomes, making them more challenging. Also, watch out for invasive species. Seeds, roots, or runners can survive composting if the pile doesn’t get hot enough, possibly causing new infestations. 

If the weeds are not seeding

To prevent weed composting issues, your compost pile must get hot enough to kill any potential seeds. This is possible with hot compost, but the method requires regular pile turning and temperature monitoring. According to the Texas A&M AgriLife Extension, the ideal temperature is between 130 and 170 degrees Fahrenheit. 

Cool compost is less labor-intensive but doesn’t generally kill weed seeds or perennial roots.

Ultimately, it’s always safer to compost young or non-seeding weeds.

If the weeds are disease- and pest-free

Some weeds may carry diseases that can survive composting if the pile is cool. If you think a weed is diseased, dispose of it. Weeds can also attract pests, so balance your compost with green and brown materials and aerate it regularly.

When can’t you compost weeds?

poison ivy in mulch
cygnus921 | Flickr | CC BY 2.0

At times, you may not be able to compost weeds. Some reasons for that:

If the weeds are poisonous

Steer clear of poisonous weeds in your compost pile – even if it’s hot compost. Certain weeds contain toxins that can survive the composting process, contaminating the pile and harming surrounding plants, animals, or humans that come into contact with them.

Some examples of poisonous weeds include:

  • Poison ivy
  • Poison hemlock
  • Poison oak
  • Wild parsnip
  • Giant hogweed
  • Stinging nettle

If you don’t have the right compost balance

When you compost the wrong weeds or don’t balance greens and browns correctly, you contribute to a nutrient imbalance, which can harm plant growth. It can also cause unpleasant odors, especially if the compost pile lacks proper aeration or you add too many fresh, green weeds at once.

If there are local limitations to composting weeds

Some municipalities or homeowner associations restrict composting certain weeds to avoid spreading invasive species or pests. If the process doesn’t kill all the seeds and roots, you risk making things worse.

FAQ about composting weeds

Which weeds can I compost?

You can compost any of the following weed types:

Which weeds shouldn’t I compost?

Skip composting invasive weed species, including:

  • Bindweed
  • Bittercress
  • Canada thistle
  • Common knotweed
  • Creeping Charlie
  • Japanese knotweed

How can I ensure my hot compost pile is hot enough to kill weed seeds?

You need to monitor the pile’s temperature and conditions. Try the following:

  • Insert a compost thermometer into the center of the pile to measure the internal temperature. The pile should hold a temperature of 130 degrees to 170 degrees Fahrenheit for around seven days to effectively kill weed seeds. 
  • Turn the pile regularly to mix the materials and distribute heat evenly. This also prevents the formation of cold spots that won’t kill weed seeds. 
  • Look for steam rising from the compost pile, especially on cooler mornings. It indicates that the pile is generating heat.
  • Replenish the pile to help maintain heat. The larger the pile, the higher the temperature. Ideally, it should be at least 3 feet x 3 feet x 3 feet, but a 3- to 5-foot square is best, says the Maryland Department of the Environment.
  • Test a small sample of compost for weed seeds. Place it in a separate container, keep it moist, and see if weed seeds germinate.

A pro can lend a hand

If DIY weed composting sounds overwhelming, don’t worry. A local weed control expert can guide you through the entire process to make it easier.

Plus, Lawn Love can connect you to a lawn care pro nearby who can mow, aerate, fertilize, overseed, and dethatch your lawn. Relying on an expert is a great way to keep your garden healthy and weed-free.

Main Photo Credit: Ciarán Mooney | Flickr | CC BY-SA 2.0

Andie Ioó

In my free time, I enjoy traveling with my husband, sports, trying out new recipes, reading, and watching reruns of '90s TV shows. As a way to relax and decompress, I enjoy landscaping around my little yard and DIY home projects.