For hot composting to fully kill all weed seeds and roots, follow these tips:
A gardener who experiences such an explosion of volunteer weeds may well swear off composting altogether, or at least stop adding weed material to the compost pile. To be clear, there is no reason to stop composting weeds. With a slight adjustment to the composting process, you can ensure that weeds and their seeds will be killed completely and won’t be resurrected where you least want them.
Compost is a great way to recycle organic material in your garden. All those spent flower blossoms, fall leaves, dead plants, grass clippings—even non-meat kitchen scraps—can be transformed into a great soil amendment and nutritious mulch, simply by throwing them into a heap and allowing the refuse to decompose naturally.
This can actually be rather charming when the volunteers are tiny impatiens seedlings, tomato plants, or even pumpkins that volunteer because last Halloween/s jack o’ lanterns were added to the compost heap. It’s far less charming when the volunteer plants are hundreds of dandelions or tiny sprigs of bindweed or crabgrass that get into the garden via the compost you spread.
In an ideal compost heap, the temperatures generated by the breakdown of plant material can get quite warm, and if temperatures exceed 145 degrees Fahrenheit, pretty much all seeds and roots will be killed. However, if the temperatures do not get warm enough—or if a portion of the compost heap does not experience sufficiently high temperatures—seeds or perennial roots can survive the composting process. When these seeds or bits of root later reach your garden inside the compost, they can—and usually do—quickly germinate or take root again.
The classic method of composting—the method purists would call the “right” way—is known as hot composting. This simply means that you turn the pile regularly and allowing it to really heat up to 145 degrees Fahrenheit or more. 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.
Done correctly, composting creates a sterile organic material that does nothing but good things for your garden and the plants in it. However, nearly every gardener who practices composting has occasionally experienced “volunteer” plants sprouting up in the garden where the compost has been spread.
Preventing weeds from taking over your garden is the first step to a weed-free garden. Even in the best of cases, though, a few weeds get through and can be composted.
I like to call compost “black gold”. It is made up of decomposing organic matter which improves your soil, and keeps kitchen scraps and yard debris out of landfills.
The Concerns with Composting Weeds
3.) An easier method for me to take care of weeds with seeds, or with roots attached, is to ferment them in water. Place the weeds in a 5 gallon pail, cover with water, and allow them to rot and ferment for several weeks before adding to your compost pile. The water can be added to the pile, too, or use it fertilize your plants. Keep in mind that this can get pretty smelly.
Throwing weeds in the landfill means that you are throwing precious nutrients away. Instead, learn to compost them the proper way so that those nutrients can be returned to your garden soil.
It is possible to garden without ever having to dig. The best way to do this is to build a raised bed and fill the bed lasagna-style. A lasagna garden is built by layering organic materials which eventually decompose into wonderful garden soil.