Updated 23 September 2026. This post used to tell you that chickens could have small amounts of onion in moderation, and it gave a list of tips for feeding it to them. That was wrong, and I have rewritten it. The extension service I check feeding questions against tells keepers to avoid onions altogether, and nobody publishes a safe amount for a hen. Tomatoes are a different story, and the ripe fruit is still fine.
The short answer: ripe tomatoes yes, as a treat. Onions no — not raw, not cooked, not powder, not the green tops. Colorado State University Extension puts onions on its list of things to avoid feeding a backyard flock, alongside rhubarb and raw or dried beans. Ripe tomato fruit is not on anybody’s avoid list; the tomato plant is. If you are standing there with something else in your hand, the free Can Chickens Eat It? checker will tell you what the sources say about it and how much your flock can have today.
Why I changed my mind about onions
I wrote the old version of this page from what everybody says, and everybody says a bit of onion is fine. When I went back through it against the sources I now use for every feeding answer on this site, it did not hold up.
Here is what those sources actually say.
- Colorado State University Extension, writing about feeding backyard poultry, lists what not to feed: avoid undercooked or dried beans, onions, and rhubarb. No quantity, no “in moderation” — just avoid.
- The Merck Veterinary Manual has a page on onion and garlic — the Allium family, which also covers garlic, leeks and chives. Eaten raw, cooked, dried or granulated, they cause a particular kind of anaemia — the sulphur-containing oxidants in Allium are, in Merck’s words, “thought to be responsible” for it. Merck names dogs and cats, and says toxicosis has been reported in production animals after feeding them onions. It does not name poultry, and I am not going to pretend it does.
- What nobody publishes is a safe amount for a chicken. Not the extension services, not the veterinary manual. The old version of this page had “1–2 slices per chicken” and “no more than 2–3% of the feed” in it. I made those numbers up from the general advice floating around, and that is exactly the kind of made-up precision I try to keep off this site.
So: an extension service says avoid them, a veterinary reference documents real harm from the same plant family in other animals, and there is no published figure to feed by. “No onions” is the only answer that cannot cost you a bird, and the cost of getting it wrong in the other direction is an onion going in the compost instead of the run.
That means all of it: raw onion, cooked onion, fried onion, onion powder and onion salt, onion rings, pickled onions, the papery skins, the green tops and the trimmings from the bottom of the veg drawer. If a scrap has onion through it — sauce, stuffing, a takeaway carton — it is a compost scrap, not a chicken scrap.
What to do with onion scraps instead
Compost them, or bin them if your compost is somewhere the flock can reach. Chickens will eat things that are not good for them if the things are there, so the answer is not to rely on them being sensible — it is to keep the onions out of the run. If you empty a kitchen caddy into the compost, empty it where they cannot get at it, and turn it in.
The same goes for the pile of scraps you mean to sort through later. I keep two containers on the counter: one for the flock, one for the compost, and onion goes in the compost one straight away rather than being decided later.
Tomatoes: the ripe fruit is fine, the plant is not
Ripe tomatoes are one of the better things to come out of a summer garden as far as a flock is concerned. They are wet, they are sweet, and hens go for them. Nothing in my sources puts ripe tomato fruit on an avoid list, and Colorado State suggests fruit and vegetable scraps of exactly this kind as treats.
The part that is not fine is the rest of the plant. UC Davis’s own feeding guide for backyard flocks lists the leaves of tomato, potato, pepper and eggplant plants, and nightshade plants generally, among the things that can be toxic. So:
- Ripe fruit only. On unripe green tomatoes my sources say nothing either way, so I do not feed them — ripe is easy to judge and costs nothing to stick to.
- No leaves, no vines, no stalks. When you clear the plants at the end of the season, that lot goes in the compost too, not over the fence.
- Nothing mouldy. Colorado State is explicit that scraps must not be mouldy. A tomato that has gone furry in the bowl is not a chicken treat.
- Chop the big ones. Cherry and grape tomatoes can go in whole; a beefsteak is worth quartering so nobody tries to run off with the lot.
- Scatter rather than pile. Spread them about and the whole flock gets some instead of the two birds at the top of the pecking order.
If your hens free-range and your tomato bed is in reach, fence the bed rather than the birds. They will strip the fruit they can reach, and they are not careful about which leaves they take on the way past.
How much of anything is a treat?
This is the number that actually matters, and it applies to tomatoes as much as to anything else.
Alabama Extension puts a laying hen’s feed at 100 to 150 grams a day — roughly a quarter of a pound. Colorado State caps treats at 10% of the daily diet. Put those together and a hen’s treat allowance is about 10 to 15 grams a day, or half an ounce, for everything that is not feed. For six hens that is a couple of handfuls of chopped tomato, not a colander full.
If you would rather go by the clock, the two sources disagree and it is worth knowing both: Colorado State says feed no more than they can clear in 5 to 10 minutes, while the University of Kentucky says no more than they can finish in 20 minutes. Either way, the reason is the one UC Davis gives plainly — the feed is balanced and the scraps are not, and a flock filling up on scraps is a flock short of the protein and calcium that go into eggs. You see that first in thin shells and fewer eggs.
The free food checker works this out for your own flock size, and it will give you the verdict and the source for any other scrap you are holding.
Growing and storing tomatoes for the flock
Tomatoes for the flock are the ones you would not put on a plate: the split ones, the ones a slug got to first, the ones that ripened while you were away. Pick them when they are fully coloured and firm, twist them off rather than pulling the truss about, and keep them at room temperature until you use them — a fridge turns the texture mealy and the hens do not care, but you may want the good ones back.
If you have a glut, they freeze. Blanch, skin, and freeze the pulp in portions; a frozen tomato broken up over the run on a hot afternoon goes down very well. What I no longer do is store onions with the flock in mind, because they are not going to the flock at all.
What I give instead
The scraps that do the job without any of this doubt, all of them things my sources either name as suitable or leave off every avoid list:
- Leafy greens — lettuce, kale, chard, cabbage. Colorado State names leafy greens first among suitable scraps.
- Cucumber, courgette and melon, especially in heat, because they are mostly water.
- Pumpkin and winter squash, seeds and all, which is the easiest autumn treat there is.
- Berries and chopped apple, minus the core and seeds.
- Cooked rice, plain pasta, plain bread and oats — Colorado State lists bread products among suitable scraps. Plain, not buttered, not salted.
- Mealworms, which count toward the 10% like everything else because they are rich, not because they are bad.
And the things I keep out of the run altogether, because a source names them: avocado skin and pit, chocolate, anything mouldy or rotten, salty or greasy food, raw or dried beans, rhubarb, green potato and potato peelings, the leaves of the nightshade family, and onions.
Sources
- Colorado State University Extension — Raising Poultry the Organic Way: Disease Control and Feeding (Howard Enos, December 2019, reviewed August 2025): the avoid list, the 10% treat cap and the 5–10 minute rule.
- UC Cooperative Extension / UC Davis School of Veterinary Medicine — Feeding your Flock (Dr Maurice Pitesky and Dr Nancy Reimers): the nightshade leaves, and treating scraps as a treat rather than the main course.
- Merck Veterinary Manual — Garlic and Onion (Allium spp) Toxicosis in Animals (Cristine Hayes DVM, last updated September 2024): what Allium does to red blood cells, and the species it has been reported in.
- Alabama Cooperative Extension System — Feeding the Laying Hen (Pacheco, Gulizia & Downs, August 2022): 100–150 g of feed a day.
- poultry.extension.org — Feeding Chickens for Egg Production in Small and Backyard Flocks (Dr Jacquie Jacob, University of Kentucky): the 20-minute rule.
Sources checked 22 September 2026. I keep chickens; I am not a veterinarian. If a bird has eaten a pile of onion and is off her food, weak or sitting fluffed up, ring an avian vet rather than working from a web page — including this one.
Related read: How to Raise Chickens for Eggs — Instant PDF download. Secure checkout by Stripe
