can you compost hay?
Yes, but hay arrives with seed heads and a real chance of herbicide residue — it is the riskier cousin of straw.
breaks down in 3–9 months; spoiled hay breaks down fastest
C:N ≈ 30:1
which bins can take it?
- hot pile caution
- cold pile caution
- worm bin caution
- bokashi no
- tumbler caution
- curbside yes
- hot pile: Heat handles the seed but not herbicide residue — know the field history before that compost meets vegetables.
- cold pile: A cold hay pile grows its own crop; expect to weed the top of it all season.
- worm bin: Chopped weathered hay makes fine bedding, but fresh green hay heats and can drive worms out of the bin.
- tumbler: Cut it short or the stems bind the drum, and keep the load light so it still tumbles.
why?
Hay is whole forage cut green and dried, so every bale carries the plant's seed load and far more nitrogen than straw, sitting near 30:1 — close to the ideal pile ratio by itself. It lands on both sides of the green-brown line for that reason: the stems supply the carbon and the leaf supplies the nitrogen, so a bale can heat on its own rather than needing a partner material. That completeness is also the problem: grass and legume seed sprouts readily in a lukewarm pile, and broadleaf herbicides sprayed on hayfields pass through composting intact.
how to prep it
- Use spoiled or weathered hay when you can get it
- Wet every layer as you build
- Ask the seller whether the field was sprayed with a broadleaf herbicide
watch out for
- The killer-compost cases extension services have documented since 2008 trace back to hay and to manure from animals that ate it — the residue survives the animal, the pile, and the season.
- Hay costs far more than straw for the same structural job; buy it for compost only when it is spoiled and cheap.
- Seed heads mean a lukewarm pile will sprout a lawn across its own surface.
often confused with
- Straw — Straw is stalk only and nearly seed-free; when you want a brown for structure, it is the cheaper and safer buy.
quick answers
Why did my tomatoes curl after I used compost with hay in it?
That is the signature of pyridine-carboxylic-acid herbicide damage. Tomatoes, beans, peas, and potatoes show cupped, fern-like leaves at residue levels as low as one to three parts per billion — far below anything you could see or smell.
Is alfalfa hay different from grass hay?
Yes. Alfalfa is a legume running near 15:1, so it acts as a strong green and heats a pile quickly, while weathered grass hay behaves more like a mild brown.