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How to grow cat grass: sow, water, and avoid mould

Updated: 21 October 2026

You have either a Webbox carton on the counter or a posted pot that looks tired after the van, and the cat is already interested. The next fortnight is the part that goes wrong: too much water on a seed tray, harsh sun on young cereal, or a Zumula left to dry out because you treated it like wheatgrass. That is how to grow cat grass. Which product to buy sits on the [cat grass plant comparison](/hub/houseplants/cat-grass-plant) and on the [buying guide](/hub/houseplants/cat-grass-plant/sub/cat-grass-plant-buying-guide). Peter F. checked the listings. This is not a lab test. A qualifying amazon.co.uk purchase can earn us a commission at no extra cost to you.

You have either a Webbox carton on the counter or a posted pot that looks tired after the van, and the cat is already interested.

Our top picks

Webbox Webbox wheatgrass kit

Best overall

Webbox Webbox wheatgrass kit
8.8/10about £6.10
View offer
Cat Mommy Cat Mommy one 12 cm pot

Rank 2

Cat Mommy Cat Mommy one 12 cm pot
7.6/10about £10.99
View offer
Carbeth Plants Carbeth Zumula 13 cm pot

Alternative

Carbeth Plants Carbeth Zumula 13 cm pot
7.8/10about £11.49
View offer
On this page
  1. 1.Start with what arrived
  2. 2.Sow the Webbox kit
  3. 3.Keep a posted cereal pot
  4. 4.Keep Zumula moist, not sun-baked

Start with what arrived

Name the object before you water it. The Webbox 120 g kit is seeds, and the listing does not print the four steps it mentions, so the sequence below is the brand page, not a trial. A Cat Mommy or generic cereal pot is already grown. Cat Mommy states no light level. The generic bullet says a sunny spot, which clashes with grower pages that keep young cereal out of direct sun. Zumula is a sedge in a 13 cm pot. The one-pot listing wants bright indirect light, moist soil and lists a 30 cm height. The RHS profile for Cyperus alternifolius is not a size for this cultivar. A yellow cereal pot is a delivery complaint. Photograph it and tell the seller.

Sow the Webbox kit

Webbox's page says six drainage holes, seed mixed with the mineral soil, and about 500 ml of water. Shoots in three to four days, and about 4–5 cm in seven to ten days, kept damp and out of direct sun. The amazon.co.uk description, checked on 19 October 2026, says about 400 ml. Follow a volume printed in your leaflet. If none is printed, do not average the two figures. The brand names mould when the tray is waterlogged. My Cat Grass says indirect sun at 16–19°C. That is shop guidance. For young cereal, follow the grower pages rather than the generic sunny-spot bullet. Do not stand this tray in a deep water bath. That habit is for umbrella sedge.
Webbox Webbox wheatgrass kit

Testsieger

Webbox Webbox wheatgrass kit
8.8/10about £6.10
View offer

Keep a posted cereal pot

A ready mix of wheat, barley, rye and oats has already grown elsewhere. The generic seller says up to two weeks. Cat Mommy reviews describe drying within days, and one buyer replaced pots every 12 to 14 days. Do not plan a season from a 12 cm pot. Firm spilled compost without leaving a puddle. Fruit flies appear in the three-pot reviews, including a pot dead within 48 hours. Mites appear on a repurchase in the shared generic reviews. Bag a fly-blown pot, and tell the seller about heat damage while the photo still matches delivery. Water will not revive grass that arrived dead. When the blades are brown and nothing new appears, throw the pot away. Lawn seed is not the refill. PDSA and Cats Protection warn that seed can lodge in an ear, an eye or a paw.

Keep Zumula moist, not sun-baked

Zumula wants moist compost, not a waterlogged seed tray. Carbeth's one-pot line says bright indirect light, soil kept moist and older shoots trimmed. The sunlight field says partial shade. The RHS species profile allows a shallow water tray for umbrella plant. That is not permission to drown a Webbox kit, and it is not a height for 'Zumula'. The two-pot listing only says simple watering. Both plants still need compost that does not dry out. Zooplus Magazine says the blades can cut the mouth or lodge in the throat. The soft-cereal alternative is on wheatgrass versus Zumula. A blade in the nose, a seed in the ear, eye or paw, continued vomiting, or any suspicion of a lily needs a vet. PDSA treats a gut blockage as urgent.

Common questions

How long until a kit is ready to nibble?
Webbox's site says shoots in three to four days and about 4–5 cm in seven to ten days. Amazon reviewers often say growth within days, and some say ready around five or six days. Those are different clocks for different stages. Shoots are not a finished chew. Keep the cat off the tray until there is a short blade, and keep the compost damp rather than flooded.
How much water does the Webbox tray take?
The brand page says about 500 ml. The amazon.co.uk description has said about 400 ml. The amazon.co.uk listing does not print a figure, and the special-features line only promises four steps without listing them. Follow a volume printed in your own leaflet. If nothing is printed, do not average the two public numbers into a third. Stop before the tray sits waterlogged, because that is when the brand says mould appears.
Why did the grass go mouldy?
Webbox names waterlogging as the cause on a kit: drainage holes blocked, or the tray left standing in water. A cereal pot can also arrive already tired and then grow flies if the compost stays wet and the blades are dead. Mouldy or sharp grass is not a snack. Bin a fuzzy tray. Do not feed grey growth to the cat and call it fibre.
How do I water Zumula?
On the one-pot Carbeth listing, keep the soil consistently moist and do not let it dry out, in bright indirect light, and trim older shoots. The RHS species profile for umbrella plant adds a shallow tray of water and filtered light. That shallow tray is for the sedge, not for a wheatgrass kit. The two-pot listing is vaguer, so use the one-pot care line rather than a splash when you remember.
The pot arrived yellow. Is that how I grow it?
No. Yellow cereal grass and yellow Zumula after a dark or hot journey are review complaints about delivery, not a target. Photograph the pot and tell the seller while it still looks like the delivery. You can try indirect light and careful water on a plant that is still alive. You cannot grow a satisfactory plant out of compost that arrived dead.

Related pages

Cat grass for indoor cats

Cat grass plant

Best cat grass plant in the UK: top pick and value

Cat grass plant buying guide: a kit, pot, or Zumula

Wheatgrass vs cat grass plant: soft blades or sedge

Sources

Public UK sources named below. amazon.co.uk prices, stars and review counts on these seven listings are the snapshot in the comparison files. A live check on 19 October 2026 had the Webbox kit nearer £6.58. Page updated 21 October 2026.

  1. PDSA, weird things cats do (retrieved 19 October 2026)
  2. PDSA, vomiting in cats (retrieved 19 October 2026)
  3. Blue Cross, why cats eat grass (retrieved 19 October 2026)
  4. Cats Protection, why cats eat grass (retrieved 19 October 2026)
  5. Cats Protection, keeping your cat safe (2025) (retrieved 19 October 2026)
  6. GOV.UK pet food (retrieved 19 October 2026)
  7. Consumer Rights Act 2015, section 19 (retrieved 19 October 2026)
  8. Zooplus Magazine, cat grass (retrieved 19 October 2026)