Yes, chickens can eat kale and spinach, raw or cooked, as a treat. They just aren’t the same treat. Kale is the better pick for laying hens. Spinach is fine in a small handful, but it does next to nothing for eggshells.
This page used to say kale and spinach give hens calcium for solid eggshells. For spinach that was wrong, and it’s the main thing this rewrite fixes. Spinach is loaded with oxalate, and oxalate grabs calcium and holds on to it. In a study on people, only about 5 percent of the calcium in spinach got absorbed.
I rewrote this page from 19 sources, and they’re all listed at the bottom. The calcium facts come from two absorption studies and a review of oxalate in food. The egg facts come from three hen feeding trials and a yolk color study. The feeding rules come from Alabama Extension, Colorado State, UC Davis and the Merck Veterinary Manual. Where something is my own math or my own call, I’ll say so.
The short version.
- Both are fine for hens as a plain treat, raw or cooked.
- Kale is the pick for a laying flock. Its calcium is easy to absorb, and a Danish trial that fed fresh kale got heavier eggs.
- Spinach locks up nearly all of its own calcium. Feed it if your birds like it, but don’t count it as calcium.
- Both turn yolks a deeper color.
- A hen’s whole treat share is 10 to 15 grams a day. That’s about half to three-quarters of a cup of chopped kale.
- Shell calcium comes from layer feed and oyster shell. Greens are the side dish.
Kale and Spinach Aren’t the Same Treat
Most pages lump these two together, and on paper they look alike. USDA’s FoodData Central puts raw kale at 89.6 percent water and raw spinach at 91.4 percent. Both have a little under 3 grams of protein per 100 grams. Alabama Extension wants layer feed at “16% or more” protein. So either green has under a fifth of the protein in the feed bag (my math).
Where they split is calcium. Raw kale has 254 milligrams of calcium per 100 grams, and raw spinach has 99. The bigger difference is what comes along with that calcium.
Spinach is full of oxalate. A 1999 review from Lincoln University in New Zealand, by S. C. Noonan and G. P. Savage, says some spinach varieties “contain 400 to 600 mg/100 g, while others range from 700 to 900 mg/100 g”. Kale barely has any. The Oxalosis and Hyperoxaluria Foundation keeps an oxalate list for people with kidney trouble. It puts raw kale at 10 milligrams per 100 grams and boiled spinach at 567.
That one number explains most of this page.
Kale Is the Better Pick for Laying Hens
A 1990 study by Heaney and Weaver at Creighton University measured how much calcium 11 women absorbed from kale and from milk. Kale won. They absorbed 41 percent of the calcium in kale and 32 percent of the calcium in milk. Their summary calls kale “a low-oxalate vegetable” that “exhibits excellent absorbability for its calcium”.
That was people, not chickens. I couldn’t find the same test run on hens. Still, it’s the best measure I found of whether the calcium in a leaf is usable at all.
The hen side comes from Denmark. In organic egg production, the study notes, “forage material as part of the diet for laying hens is mandatory”. So two researchers at Aarhus University tried several kinds on 300 organic layers for 5 weeks. Every hen was offered organic feed plus 120 grams a day of forage, and for one group that forage was fresh kale leaves. The others got corn silage, some of it mixed with basil or thyme.
Here’s what they reported for kale. “Feed intake, forage intake and laying rate did not differ with treatment, but egg weight and egg mass produced increased significantly with the kale treatment”. Shell strength “tended to be higher” with kale. Yolks came out redder. A tasting panel found the kale eggs had “less sulphur aroma” and whites that tasted “more sweet and less watery”.
Don’t read 120 grams a day as permission to dump a bushel in the run, though. That was a planned trial with a full organic ration in front of the birds, and it ran five weeks. Kale’s good calcium is also a small amount. At 254 milligrams per 100 grams, it has about a twelfth to a sixteenth of the calcium in layer feed at 3 to 4 percent (my math).
One more thing in kale’s favor is winter. Massey University’s poisonous-plant guide says kale “used to be mainly a cold weather winter feed, as it is frost resistant”. That’s handy in the cold months, when the run’s gone to bare dirt and the flock has nothing green to pick at.
Spinach Locks Up Its Own Calcium
Two years before the kale study, the same Creighton team, with Recker added, ran spinach against milk in 13 adults. Each test meal carried 200 milligrams of calcium. They absorbed 27.6 percent of the calcium from milk and 5.1 percent from spinach. Their test spinach had a hair more oxalate than calcium, so they concluded “it is likely that all of the spinach Ca was effectively bound”.
Bound means locked up. As Noonan and Savage put it, “oxalates bind calcium and other minerals”. They sort foods by how much oxalate they carry for each unit of calcium. Spinach sits in their worst group, with a ratio over two, next to rhubarb, beet leaves and sorrel. Their verdict is blunt: “Rhubarb, sorrel, beet and spinach are not good sources of calcium despite their apparently high levels”.
They also say a food in that group carries “excess oxalate which can bind calcium in other foods eaten at the same time”. That sounds scary for a laying hen, so I ran the numbers. One oxalate ties up one calcium, which works out to about 0.44 milligrams of calcium per milligram of oxalic acid. A 10 to 15 gram spinach treat at 400 to 900 milligrams of oxalic acid per 100 grams has 40 to 135 milligrams of it. After it’s done binding the spinach’s own calcium, it could grab at most around 45 milligrams more. A day’s layer feed carries 3,000 to 6,000. (All of that is my math, from the sources above.)
So a handful of spinach isn’t going to rob a hen’s shells. It just doesn’t add to them. The trouble starts with big amounts. The Merck Veterinary Manual says the low blood calcium that soluble oxalate can cause “is more readily seen in livestock grazing large quantities of plants containing soluble oxalates”. And Noonan and Savage note that “Oxalic acid accumulates in plants especially during dry conditions”, so a garden row that’s been through a long dry spell isn’t the one I’d strip for the flock.
Both Turn Yolks a Deeper Color
Here’s where spinach pulls its weight. A 2021 Purdue University study puts it plainly: “Hens are not able to synthesize carotenoids”, so “the color of the yolk is derived from the carotenoid pigments present in their feed”.
Dark greens are packed with those pigments. FoodData Central lists 6,260 micrograms of lutein and zeaxanthin per 100 grams of raw kale. Raw spinach has 12,200, close to double.
Both show up in the trials. The Danish kale hens laid eggs with more lutein and beta-carotene and yolks that were redder and yellower. In a 2026 study from Türkiye, 180 Lohmann Brown hens, 86 weeks old, got 0.1 percent spinach leaf powder in their feed for 84 days. Egg mass and hen-day production went up, and the authors say spinach gave “the greatest pigmentation response”. Most shell traits and blood calcium didn’t change.
That 0.1 percent is tiny. In 100 to 150 grams of feed, it’s 0.1 to 0.15 grams of dried powder. Fresh spinach is about 8.6 percent dry matter, so that’s very roughly 1 to 2 grams of fresh leaf a day (my math, assuming the powder held little water). Small amounts can deepen a yolk, in other words.
A German study for organic farms got the same result from a mix of marigold flowers and spinach, three parts spinach to one part marigold. Yolks went from 4.7 on the Roche color fan with no added pigment to between 8.0 and 8.9 with the mix.
How Much Kale or Spinach a Hen Gets
Colorado State Extension says “Treats should make up no more than 10% of their daily diet”. Alabama Extension says a laying hen eats “between 100 and 150 grams of feed per day”. So her whole treat share is 10 to 15 grams a day, and that covers every treat, not just greens (my math).
In kitchen terms, USDA’s cup of chopped raw kale weighs 21 grams and a cup of raw spinach weighs 30. That makes one hen’s share about half to three-quarters of a cup of kale, or a third to half a cup of spinach (my math). For a flock of 10, that’s 5 to 7 cups of kale on a day with no other treats.
The old version of this page said 1 to 2 cups for 10 birds, two or three times a week. That works out to 2 to 4 grams of kale or 3 to 6 grams of spinach a bird. That’s well inside the share, so it wasn’t bad advice. It just had nothing behind it.
Going over the share is where greens cause trouble. Jacquie Jacob of the University of Kentucky warns that “excessive table scraps and greens can adversely affect egg production”. She lists “Regularly adding green chops, lettuce, or other low nutrition ingredients to the diet” as a common feeding mistake. Yuko Sato in the Merck manual says “birds should receive most of their diet from a balanced, nutritionally complete ration”. UC Davis puts it best: “treat the scraps like a treat not like the main course”.
Colorado State adds a timing rule I like. “Do not feed more than can be consumed in 5 – 10 minutes to not attract nuisance animals”. Greens left lying in the run overnight end up feeding more than chickens. Colorado also says to give birds “free access to grit and a calcium source like oyster shell or eggshells”, and that’s where the shell calcium really comes from.
Kale Is a Brassica. Should That Worry You?
If you read up on kale as livestock feed, you’ll run into two scary words: anemia and goiter. Both are real, and both come from animals grazing whole fields of it.
Massey University says a compound in brassicas, S-methylcysteine sulphoxide, “is responsible for kale anaemia”, and that “This only occurs in ruminants, usually after 1 – 3 weeks on brassicas”. A University of Kentucky sheet by Michelle Arnold and Jeff Lehmkuhler explains why. In the rumen, the compound “is converted to dimethyl disulfide”, which ends up damaging red blood cells. It says the anemia is worst in cattle that have grazed kale or other brassicas for one to three weeks.
Goiter works through the thyroid. Massey says brassica glucosinolates “block the production of thyroid hormone and can cause goitre”, and “Wintering ewes on kale can lead to severe goitre in lambs”. Kentucky says that’s “more of a concern with sheep and goats”.
A hen isn’t a ruminant, and none of the sources I read reported either problem in chickens. Kentucky’s own advice for cattle is that brassicas “should not constitute more than 70 percent of the animal’s diet”. A treat share is capped at 10 percent. And the Danish hens were offered 120 grams of fresh kale a day for five weeks with no change in laying rate. So as a treat, I don’t worry about it. If you planted a kale patch and let the flock graze it as most of their diet all winter, that’d be a different story, and I’d keep the feeder full.
Raw or Cooked, and What Stays Out
Raw is fine. If you cook it, cook it plain. Colorado State says kitchen scraps for the flock should not be “salty or have citrus or are moldy”, so skip the butter and salt you’d put on yours.
Cooking does pull some oxalate out of spinach. Weiwen Chai and Michael Liebman at the University of Wyoming found that boiling “markedly reduced soluble oxalate content by 30-87%”, and steaming only cut it by 5 to 53 percent. The oxalate didn’t vanish, though. They found “an approximately 100% recovery of oxalate losses” in the cooking water. If you boil spinach for the birds, pour that water down the drain (my call). Even boiled, spinach is still near the top of the oxalate list, so cooking doesn’t turn it into kale.
The bag of spinach that went slimy in the back of the fridge goes in the trash or the compost, not the run. Jacob says to make sure scraps “are not allowed to rot, or botulism might result”. UC Davis says scraps should be “still good quality”.
Garden greens need one more check. Vermont Extension says fertilizers, fungicides, pesticides or other chemicals “may be harmful to the chickens”, organic ones included. If the kale was sprayed, read the label for how long to wait before anyone eats it, and don’t hand the flock leaves sooner than you’d eat them yourself (my call).
Keep the Flock Out of the Greens You’re Growing
If you grow kale or spinach yourself, the flock will find it. Deborah Benoit at the University of Vermont Extension doesn’t sugarcoat it. “Once you’re ready to plant, ban them from the garden. They’ll eat newly sown seeds and emerging seedlings”. And “In the blink of an eye, they’ll defoliate young plants”.
Her fixes are simple. “Portable fences can discourage chickens, and row covers or bird netting can provide a barrier between chickens and a forbidden feast. Wire cloches can protect small plants”. For a bigger garden, she suggests “a double fence spaced about four feet apart around the garden”, so the flock can patrol the gap and catch bugs on their way in.
She also says to let the flock clean up “At the end of the growing season”, after you’ve pulled the plants that aren’t safe for them. A spent kale row is a good one to hand over. Until then, pick the leaves and carry them to the run. That keeps the treat share honest and keeps the plants alive (my call).
The Other Greens: Collards, Lettuce, Chard, Beet Leaves
If you remember one thing from this page, make it the oxalate list. Here’s how the usual garden greens fall, using the Oxalosis and Hyperoxaluria Foundation’s numbers per 100 grams raw.
- Collards sit with kale. They have 17 milligrams of oxalate and, per FoodData Central, 232 milligrams of calcium.
- Lettuce and green cabbage are low too, at 5 milligrams each. Noonan and Savage put both in their best group. Romaine is 94.6 percent water with 33 milligrams of calcium, though, so it’s mostly a drink. That’s the “low nutrition” lettuce Jacob warns about.
- Swiss chard sits with spinach. Green chard has 657 milligrams of oxalate and red chard has 1,167. Noonan and Savage’s review (they call it silverbeet) notes that “Spinach, orach and silverbeet are generally eaten after being boiled”.
- Beet leaves are in spinach’s group too. So is rhubarb, and Vermont Extension lists rhubarb among the crops “unsafe for chickens to consume”. Keep rhubarb leaves out of the run.
Purslane, the weed that pops up in garden cracks, is another high-oxalate green. I went through it on the purslane page.
What I’d do
- Pick kale over spinach for laying hens when you’ve got the choice.
- Feed spinach for the yolk color and because hens like it, a third to half a cup a bird at most.
- Keep every treat together under 10 to 15 grams a hen a day, and pick up what’s left after 10 minutes.
- Give it plain. Cooked spinach is fine, but pour off the cooking water.
- Toss anything slimy or moldy. Don’t feed sprayed garden leaves before you’d eat them.
- Leave layer feed and oyster shell out, since that’s where the shell calcium comes from.
Our can chickens eat it checker rates leafy greens as a treat, and that includes kale and spinach. For the foods that never go in the run, see what you shouldn’t feed chickens. And if you’re raising chicks, their greens go in chopped small with a dish of chick grit beside them, so read can baby chicks eat fruits and veggies first.
Sources
- R. P. Heaney and C. M. Weaver: Calcium absorption from kale (American Journal of Clinical Nutrition 51(4), 1990).
- R. P. Heaney, C. M. Weaver and R. R. Recker: Calcium absorbability from spinach (American Journal of Clinical Nutrition 47(4), 1988).
- S. C. Noonan and G. P. Savage: Oxalate content of foods and its effect on humans (Asia Pacific Journal of Clinical Nutrition 8(1), 1999).
- Oxalosis and Hyperoxaluria Foundation: Vegetables Oxalate.
- Weiwen Chai and Michael Liebman: Effect of different cooking methods on vegetable oxalate content (Journal of Agricultural and Food Chemistry 53(8), 2005).
- Renee D. Schmid, Merck Veterinary Manual: Houseplants and Ornamentals Toxic to Animals.
- M. Hammershøj and S. Steenfeldt: The effects of kale (Brassica oleracea ssp. acephala), basil (Ocimum basilicum) and thyme (Thymus vulgaris) as forage material in organic egg production on egg quality (British Poultry Science 53(2), 2012).
- Yonis Saab Najim and co-authors: Effects of spinach and Labada leaf powders with or without NSP-degrading enzymes on performance, egg quality, and yolk pigmentation in late-phase laying hens (Poultry Science 105(12), 2026).
- Angela Sünder and co-authors: Egg yolk colour in organic production as affected by feeding (Food Chemistry 382, 2022).
- Darwin Ortiz and co-authors: Biofortified orange corn increases xanthophyll density and yolk pigmentation in egg yolks from laying hens (Poultry Science 100, 2021).
- Massey University, Poisonous Plants: Cabbage and other brassicas.
- Michelle Arnold and Jeff Lehmkuhler, University of Kentucky: Forage-Related Cattle Disorders, Brassicas: Be Aware of the Animal Health Risks (ID-223).
- Deborah J. Benoit, University of Vermont Extension: Chickens in the Garden (2024).
- Jacquie Jacob, Poultry Extension: Feeding Chickens for Egg Production in Small and Backyard Flocks.
- Colorado State University Extension: Raising Poultry the Organic Way: Disease Control and Feeding.
- Wilmer Pacheco and co-authors, Alabama Cooperative Extension: Feeding the Laying Hen (ANR-2913).
- Maurice Pitesky and Nancy Reimers, UC Davis: Feeding your Flock.
- Yuko Sato, Merck Veterinary Manual: Management of Backyard Poultry.
- USDA FoodData Central: Kale, raw (FDC ID 168421), Spinach, raw (168462), Collards, raw (170406), Lettuce, cos or romaine, raw (169247) and Chard, swiss, raw (169991).
Sources checked October 27, 2026. The treat share, the cup sizes, the protein and calcium comparisons, the oxalate binding and the spinach powder conversion are my math from these sources. Choosing kale over spinach, pouring off the cooking water, the spray wait and keeping the flock out of a growing bed are my own calls. We aren’t vets. If a hen seems off after eating a lot of any green, call a vet who sees poultry.
Related read: How to Raise Chickens for Eggs — Instant PDF download. Secure checkout by Stripe
