can you compost weeds with seeds?
Only in a pile that truly runs hot — otherwise you are quietly reseeding your garden every time you spread compost.
breaks down in 1–3 months, though the real question is temperature
C:N ≈ 20:1
which bins can take it?
- hot pile caution
- cold pile no
- worm bin no
- bokashi no
- tumbler caution
- curbside yes
- hot pile: Works only if you turn the outside in at least twice and a probe thermometer reads 131°F or better.
- tumbler: Small tumblers rarely hold killing heat; treat the output as seed-contaminated unless a thermometer says otherwise.
why?
A seed is a dormant embryo inside a hard protective coat, and heat is what kills it: most common weed seeds die after roughly 30 minutes at 140°F. Some are far tougher — pigweed and lambsquarters seed has come through composting alive — and every pile has cool edges where nothing gets that treatment.
how to prep it
- Seal seed heads in a black plastic bag and leave it in the sun 4–6 weeks
- Or snip the seed heads off, trash those, and compost the rest of the plant
- Bury the material in the hottest core of the pile
watch out for
- A compost thermometer is the only way to know; piles smaller than about 3 feet cubed usually cannot hold heat long enough.
- Tomato, squash, and sunflower seeds survive cool piles too — volunteers sprouting in next spring's beds are the tell.
- Commercial facilities run windrows above 131°F for weeks, so curbside yard-waste collection is the dependable answer.
often confused with
- Weeds pulled before flowering — Pulled young and seedless, the very same plants are an easy yes in any pile.
quick answers
How hot does compost have to get to kill weed seeds?
131°F is the floor and 140°F is comfortable. The USDA National Organic Program standard of 131–170°F for 15 days with five turnings exists precisely because that combination reliably sterilizes seed and pathogens.
Does solarizing weeds in a bag actually work?
Yes. Sealed black plastic in full summer sun runs well past 140°F inside, and four to six weeks reduces seed heads to slimy dead biomass that is safe for any pile.