You can compost weeds by combining them with food scraps, kitchen waste, or other plant materials to create a finished compost rich in nutrients. However, hot composting is recommended in order to destroy weeds effectively and avoid seeds from sprouting.
The cold compost pile heats up as plants inside break down. Weed seeds die when the temperatures are high enough. But the heap might not become hot enough to kill the weeds or may contain cooler pockets that are home to weeds.
Also, small home composting methods like using a trash can or plastic storage bin composter are not recommended as they cannot maintain consistent high temperatures.
However, there are still a few options available to you:
- If your compound is sizable and well-monitored, you can compost your weeds in a hot compost.
- Sun drying will destroy the weed seeds.
- Before putting them into your compost, give the weeds a good soak in water.
- Separately compost the weeds in black plastic bags.
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Are Weeds Green or Brown Material?
Weeds are considered green materials in their fresh state because of their high nitrogen content (2.53%).
You can compost them as brown material once they’ve dried because they’re high in carbon.
Check our video below on how to compost weeds while avoiding weed seeds in your compost pile.
How Long Does It Take for Weeds to Decompose?
Usually, weeds take six to eight months to break down fully.
Whether they are hot or, cold composted will determine how long it takes. Also, whether you use a compost tumbler, trash can, or heap will affect the decomposing time.
You can also try sun-drying weeds for 2 to 3 weeks or soaking weeds for 2 to 3 months; these processes will kill the weeds and their seeds, but it won’t break them down completely.
Weeds composted in a black plastic bag can take two years or fewer to decompose completely.
How to Compost Weeds
The different methods for composting weeds along with their seeds include:
1. Hot Composting
Hot composting entails turning your pile frequently and enabling it to reach a temperature of 145 degrees Fahrenheit.
If you can properly manage your hot compost pile, you don’t have to be concerned about the weeds reappearing in your garden since the high temperatures kill weed seeds and pathogens.
Follow these recommendations to ensure that hot composting destroys all seed heads and roots:
- Turn your pile frequently. Every compost heap has separate cool areas that take longer to decompose. Frequent mixing of the pile ensures that all the material reaches the required temperature to destroy the roots and seeds.
- Allow some time. When done correctly, hot composting includes fully decomposing an amount of material until it has completely broken down. Instead of continuing to add little quantities of more material to the pile, start a new one while the current heap is breaking down completely. Your compost is ready when you note that stirring the composted materials does not cause it to heat up.
- Weed your garden. If your garden has weeds, adding the fresh compost will only feed the weeds and your plants because it is so rich in nutrients. Therefore, before introducing the new compost to your garden soil, ensure it has been well weeded.
2. Cold Composting
Cold composting doesn’t require continuous mixing or temperature monitoring. While microorganisms or microbes work on the lower layers (decomposing them), gardeners can continuously add new material, like kitchen scraps, to the compost bin or heap.
Although it usually takes a little longer, cold composting is simple.
Below are a few pointers for keeping your cold compost weed-free:
- Keep noxious weeds out of your compost. It is preferable to leave some perennial weeds out of your cold compost pile entirely because you’ll need a lot of heat to destroy them. These weeds include oxalis buttercups, morning glory, bermudagrass, crabgrass, and quackgrass. Also, keep out of a cold compost pile garden plants that spread through runners, like raspberry canes or mint.
- Don’t compost weeds set to seed. If you feed annual weeds to a cold compost pile before they mature, they rarely cause any issues. But suppose you toss the dandelion flower heads into your heap after producing hundreds of seeds. You risk having a dandelion avalanche when the heap is eventually placed on the farm.
- Burn the weeds. Almost any plant can be made compost-safe by heating it to the point where the roots and seeds are destroyed. There are various methods for doing this. For instance, you may solarize the weeds by putting them in a black plastic bag and baking them in the sun. Other gardeners use a metal sheet placed in the sun to bake weeds, which are safe to compost because they have dried to a crisp.
Can You Compost Weeds Killed With Herbicides?
Weeds treated with herbicides should be kept out of your compost to protect your garden against poisons.
When you collect green and browns for creating your compost, persistent pesticides on the materials you use may still be present after the composting process.
If you still want to compost weeds treated with herbicides, compost them separately and use them on plants less susceptible to herbicides. Avoid using the resulting compost on food crops.