Composting Weeds

Dos, Don'ts, and Things to Watch Out For

Compost bin in a backyard vegetable garden
David Freund/Photodisc/Getty Images

Composting is a great way to recycle in your garden. You turn all of those spent flower blossoms, fall leaves, dead plants, and grass clippings into something that will make every plant in your garden grow better. I wish we could get everyone on the composting bandwagon! So when I get an email like this, it's disheartening, because I hate to see people turned off of composting by something so preventable:

"I started my first compost pile a couple of years ago. While it's been nice not sending so much garbage to the landfill, I don't think I'll be doing much composting anymore. I spread my finished compost on my new vegetable garden, and it is now loaded with weeds such as dandelion and bindweed. I shouldn't have thrown all of those weeds in the compost. I wish I'd known that when I started!"

You do have to be a bit careful when composting weeds. The last thing anyone wants is to infest their garden beds with a plethora of weeds from their compost! Luckily, there are a few simple tips that will help you keep your compost weed-free, even if you're composting weeds.

1. Practice Hot Composting

Hot composting merely means that you turn the pile regularly and allow it to really heat up. A properly maintained hot compost pile will kill weed seeds, as well as many other pathogens, so you can compost weeds without having to worry about them popping up in your garden beds.

Many gardeners tend to compost in a more passive manner, also known as "cool" composting. The rest of the tips in this article are for you.

2. Don't Compost Weeds That Have Gone to Seed

If you are going to throw weeds into your compost pile, be sure that they haven't set seed, first. The email writer I referenced above-mentioned dandelions. Definitely, definitely, don't throw dandelions or anything else that has already set seed into your compost pile! Those weed seeds will just sit there happily in your compost until you spread them over a garden bed where they have access to light and air, and, wham! You've got a weed issue. If your weeds have already gone to seed, throw them in the trash. The sooner you can remove a weed from your garden, the better.

3. Avoid Composting Weeds that Spread by Runners

Mint, for example, will just laugh and merrily colonize your compost. Ditto raspberry canes, bindweed, dock, and switchgrass. If, when you're pulling it from your garden, you end up pulling one long root that attaches itself to other plants -- don't compost it, or you'll be pulling it out of your garden forever.

However, there is a trick for composting even these pesky weeds.

How to Compost Even the Most Invasive, Pesky Weeds Safely

If you're like me, you hate the idea of throwing anything green and "compostable" into the trash. So this tip is for you.

You know those weeds I mentioned above? The ones that spread by runners that you shouldn't put into your compost because they'll cause a mess? You can still compost them -- but you have to fry them first.

How to fry them, to ensure that they don't spring back to life and take over your compost (and, by extension, your garden)? Solarize them. Solarize merely means: seal them in a black plastic bag (no holes), put it in a sunny, out of the way spot in your garden. Wait a couple of months. Once the weeds in the bag are no longer recognizable, you can toss them in your ​compost pile.

I do another version of this in my garden. It might not work for everyone, but it works for us. You know those metal garden sheds? We have one of those back by our compost piles. Whenever we've spent some time weeding out anything invasive, we set the offending weeds on the metal roof of the shed. It gets HOT up there, especially in summer. We leave the weeds there for a few weeks, and then, once they're dry, crispy, and solidly dead, we go ahead and toss them into the compost.

So, you can compost weeds. And you should! You just need to take a few precautions to make sure that it doesn't end up causing problems for you later on.