Grass, garden plants and wild forage for guinea pigs: what is safe, by season

Quick answer

Everything a guinea pig eats is raw plant material. The safety question is not raw or cooked; it is which plant, how much, and picked from where.

Guinea pigs are strict herbivores. Grass, herbs and leaves are their natural diet, and fresh forage is genuinely good for them: fibre, moisture, vitamin C and something to do.

The risks are specific rather than general. Lawn mower clippings can kill. New spring grass introduced too fast destabilises the gut. And a short list of common garden and hedgerow plants is seriously toxic, several of them at small doses.

• Never feed lawn mower clippings, at any time, however fresh they look.
• Introduce grass gradually over weeks, starting with minutes rather than handfuls.
• Identify every plant before you pick it. If you are not certain, do not pick it.
• Guinea pigs cannot vomit, so anything harmful that is eaten stays in.
• Avoid verges beside roads and paths, sprayed lawns, and anywhere dogs walk.

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Lawn mower clippings kill guinea pigs.

Cutting bruises and heats the grass, and fermentation starts within minutes of it landing in the box. By the time clippings reach the enclosure, the material is already fermenting, and it continues doing so inside a gut that cannot vent gas quickly.

The result is rapid gas production, bloat and, frequently, death. Clippings also collect fuel and oil residue from the mower, are cut close to the ground where wildlife has toileted, and are usually taken from lawns that have been treated.

There is no safe version of this. Freshly mown, organic, from your own lawn, collected immediately: all of it is still clippings. Pick grass by hand instead.
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Decide in 60 seconds

Why grass is different from a bowl of vegetables

A guinea pig's gut runs on continuous long fibre fermented in a large caecum by a bacterial population that adapts slowly. Anything that changes the substrate arriving in that caecum changes the fermentation, and rapid change is what causes trouble.

Fresh spring grass is a substantial change. It is high in water and in soluble sugars, and low in the structural fibre that hay provides. Delivered in volume to a gut that has spent the winter on hay, it produces a burst of fermentation, gas, and a shift in the bacterial population.

That is why the same grass that is entirely healthy in July causes problems in April, and why the amount matters more than the plant.

The correct approach is boring and effective. Start with a few minutes of grazing, or a small handful, once a day. Add a few minutes every couple of days over two to three weeks, watching droppings and appetite throughout. Any softening of the droppings means step back to the previous amount for several days.

The same applies at the other end of the season. A guinea pig that has grazed all summer and then has no grass for months needs reintroducing gradually the following spring, not resuming where it left off.

Plants that are safe and worth picking

These are widely eaten by guinea pigs and are straightforward to identify once you know them. Pick from clean ground, wash, and offer variety rather than a lot of any one thing.

Dandelion.
Leaves and flowers. Very well liked and a good source of vitamin A precursors. It is also relatively high in calcium, so rotate it rather than feeding a bowlful daily.

Ribwort and broadleaf plantain.
Common in lawns, easy to identify by the parallel veins in the leaf, and well accepted.

Chickweed.
A soft, sprawling low plant. Popular and gentle, and one of the safest introductions.

Bramble leaves.
Blackberry leaves are a genuine favourite and the thorns are not a problem for a guinea pig. Pick from away from paths where dogs walk.

Raspberry and strawberry leaves.
Safe and well liked, and easy to grow on purpose.

Cleavers.
The sticky climbing plant, also called goosegrass. Safe and enjoyed.

Yarrow, sow thistle and shepherd's purse.
All commonly fed once you are confident identifying them.

Nettle.
Best wilted or dried, at which point the sting is gone. Nutritious and readily eaten.

Hawthorn, apple, pear, willow and hazel.
Leaves and small branches from these trees are safe and provide chewing as well as food. Avoid stone fruit trees such as cherry and plum.

Herbs from the kitchen garden.
Coriander, basil, dill and mint are all safe. Parsley is safe but high in calcium, so it should be occasional rather than daily.

Plants to avoid

This list is not exhaustive, which is the point: the working rule is that you feed only what you can positively identify as safe, not everything you cannot identify as dangerous.

Ragwort.
Contains alkaloids that damage the liver cumulatively. It stays toxic when dried, so it is a risk in poorly harvested hay as well as in a field.

Groundsel and other Senecio species.
Related to ragwort and containing the same class of alkaloids. It appears in older forage lists as safe and should not be fed.

Foxglove.
Contains cardiac glycosides. Seriously toxic in small amounts.

Yew.
Extremely toxic, including the clippings and the dried plant. Every part except the fleshy red aril is dangerous.

Rhododendron and azalea.
Contain grayanotoxins. Toxic in small quantities.

Bracken.
Contains an enzyme that destroys thiamine, and other harmful compounds.

Buttercup.
Irritant to the mouth and gut when fresh.

Nightshades.
Deadly nightshade, woody nightshade and bittersweet, and also the green parts of potato and tomato plants.

Bulb plants.
Daffodil, tulip, hyacinth, bluebell, crocus, snowdrop. Toxic in leaf and bulb, and a spring hazard because the leaves come up in lawns.

Hemlock, lords-and-ladies, lily of the valley, monkshood and laburnum.
All seriously toxic.

Ivy, privet and most evergreens.
Including conifer trimmings, which is a winter hazard when gardens are being tidied.

Rhubarb leaves.
High in oxalates.

Avocado, onions, garlic, leeks and chives.
Not forage, but frequently offered from a kitchen and all unsuitable.

Acorns, conkers and most tree seeds.
An autumn hazard where guinea pigs have outdoor run access.

Any houseplant.
Assume unsafe unless you have specifically confirmed otherwise.

Weigh weekly through the grazing season. A guinea pig that is losing or gaining while the diet changes is telling you something.

The seasonal calendar

Early spring.
The highest-risk period. Grass is lush, sugary and low in structural fibre, guinea pigs have had a winter on hay, and bulbs are pushing up through lawns exactly where you would pick. Introduce grass in minutes, not handfuls, and check lawns for daffodil, bluebell and crocus foliage before letting a guinea pig graze.

Late spring and early summer.
Peak forage season and the best variety. Two new risks arrive: heat, because guinea pigs have very little tolerance for it and an outdoor run in the sun is dangerous, and herbicide spraying on lawns, verges and farmland. Grazing should be in shade, supervised, and never in the middle of a hot day.

Midsummer.
Grass seed heads and awns can lodge in eyes, ears and skin. Check the coat and eyes after outdoor time. Flies are also a risk to any guinea pig with a soiled rear end.

Autumn.
Windfall fruit ferments where it lies and attracts wasps, so it should not be within reach of a run. Fallen leaves accumulate and some are toxic. Acorns and conkers are a specific hazard. Grass growth slows and the sugar profile changes with cold nights.

Winter.
Very little safe forage. Frosted and frost-damaged grass, mouldy fallen material and evergreen trimmings from garden tidying are the hazards. This is the season to rely on hay and a consistent vegetable portion, and to accept that outdoor grazing is largely over.

Picking safely

Identify first.
Use a plant identification book or app, and confirm with a second source before feeding anything new. Learn a small number of species properly rather than a long list vaguely.

Choose the location, not just the plant.
Avoid road verges, car parks, footpath edges and anywhere dogs are walked, because of exhaust residue, dog urine and faeces, and the parasites they carry. Avoid field edges next to arable land because of spray drift, and avoid any lawn that has been treated.

Pick by hand.
Scissors are acceptable if the grass goes straight to the guinea pigs. What matters is that the material is not bruised, heated and left in a heap.

Do not bag and store.
Grass carried home in a sealed plastic bag heats and begins fermenting within a short time. Use a loose open container, carry it home quickly, and feed it fresh. Do not save the leftovers for tomorrow.

Wash and inspect.
Rinse in cold water, and look for slugs and snails, which carry lungworm, and for insects and bird droppings.

Feed it fresh, and remove leftovers.
Fresh forage left in the enclosure wilts, ferments and attracts flies.

Assess hay and forage by smell as well as sight. Sweet and green is right; musty, dusty or sour is not.

Grazing outdoors safely

An outdoor run is the best way to feed grass, and it introduces its own list.

Secure the run against predators from above as well as from the sides, including birds of prey, and never leave guinea pigs unsupervised in one.

Provide shade over at least part of the run at all times, and do not use it during the hottest part of the day. Guinea pigs overheat quickly and cannot cool themselves effectively.

Move the run so the animals are not repeatedly grazing ground fouled by their own droppings, and check the area for cat and fox faeces before use.

Check the ground for toxic plants, mushrooms and slug pellets before every session, not just the first time.

Keep water available in the run.

Check the coat, eyes and ears afterwards for grass seeds, and check the rear end for soiling.

Recognising the emergencies

Bloat.
A tight, drum-like abdomen, a hunched posture, reluctance to move, not eating, and sometimes drooling. It is painful and progresses fast, and it is the classic outcome of clippings or a sudden volume of fermentable material. This is an immediate emergency.

Gut stasis.
Reduced or absent droppings, refusing food, a hunched posture and teeth grinding. Also urgent.

Diarrhoea.
Watery, unformed faeces with a soiled rear. In a guinea pig this is serious rather than routine.

Suspected poisoning.
Drooling, tremors, weakness, collapse, or a sudden change after outdoor access. Take a sample of the plant with you.

In every case, keep hay available, keep the animal warm, do not fast it, do not give human medication, and go.

What the vet will ask for

• Exactly what was eaten, and how much, and when.
• A sample of the plant, or a clear photograph of it in situ, if poisoning is suspected.
• Whether the grass was mown or hand picked.
• Whether the lawn or field has been treated, and when.
• What the droppings have looked like over the last few days.
• Current weight and the recent trend.
• Whether hay intake has changed.
• Whether more than one animal is affected.
• Whether the guinea pigs have had outdoor access, and to what ground.

What never to do

Do not feed mower clippings.

Do not feed anything you cannot positively identify.

Do not increase grass quickly because the guinea pigs enjoy it.

Do not store picked grass, or feed grass that has been sitting in a bag.

Do not pick from road verges, treated lawns or dog-walking areas.

Do not feed evergreen or conifer trimmings.

Do not leave guinea pigs unsupervised in an outdoor run.

Do not graze in full sun or during the hottest part of the day.

Do not reduce hay because the guinea pigs are eating grass.

Do not wait to see whether bloat settles.

Normal droppings, a steady weight and continued hay eating are the three signals that a forage plan is working.

When to get help

Go immediately for a tight distended abdomen, a hunched guinea pig that is not eating, no droppings, drooling, tremors, weakness or collapse, and for any suspected toxic plant ingestion.

Go the same day for diarrhoea, markedly softer or fewer droppings, or a guinea pig that has become quiet after outdoor access.

Book within a few days for weight loss over consecutive weeks, repeated soft droppings when grass is offered, or grass seeds you cannot remove from an eye or ear.

Bring the plant or a photograph, the timeline, the weight record and the dropping history. In forage cases the identification of the plant changes the treatment completely, and it is something only you can supply.