How long does it take weeds to compost?

May, 2022
Darren Spalding

You can test your compost for weeds by placing it in a water-moistened bag in a warm place with a handful and see what comes to life. This won't kill seeds, but it's good for weeds with roots still attached that could potentially take root in your compost heap. A blooming compost heap should reach temperatures above 140 degrees and effectively clean your future compost humus from any trace of weeds. And when you compost them, you can not only make more compost, but you can also make a compost that's more balanced and nutritious.

Is it okay to compost weeds?

If you follow the general weed advice and remove them at a young age, the weeds will decay and quickly form excellent compost. I find that these green bags are slowly breaking down and suggest lining a compost bin with paper to keep the sides mostly clean. That's what I'm doing here. If your compost heap is getting a lot of heat and steaming, weeds can compost in just 6 to 8 months. That means I often buy bags and make my own compost with whatever is cut off in the garden.

Hello, I recently filled my compost bin and placed some grass clippings on it that form a black slimy cover.

Does composting kill weeds?

Unless you check the pH and temperatures of your compost heap daily, it's not recommended to place weeds or weed roots in your compost heap. To maintain biological activity and complete the active phase, temperatures should be monitored and compost moisture and aeration maintained. Even if something is germinated initially, the heat under the plastic will be so high that both the seedlings and any remaining seeds will soon be killed off, giving you weed-free compost that you can use as you please. When properly managed, a compost pile should easily reach 140°F, which breaks down all organic matter, including weed seeds.


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