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Geranium fertiliser buying guide: form, NPK and pack

Updated: October 2026

You have a tray of bedding geraniums, a window box, or a few patio pots, and the amazon.co.uk shelf offers two Cultivers analyses plus one Osmocote tub that does not print an NPK in the product data. This geranium fertiliser buying guide is the decision, not the product table. Name the plant, then choose a form you will actually repeat, then match the pack to the number of containers. The [geranium fertiliser comparison](/hub/fertiliser-soil-and-bark-mulch/geranium-fertiliser) lines the eight ASINs up. A qualifying purchase can earn us a commission at no extra cost to you.

You have a tray of bedding geraniums, a window box, or a few patio pots, and the amazon.co.uk shelf offers two Cultivers analyses plus one Osmocote tub that does not print an NPK in the product data.

Our top picks

Cultivers Cultivers organic geranium and flowering plant fertiliser 250 g

Best overall

Cultivers Cultivers organic geranium and flowering plant fertiliser 250 g
10.0/10about £11.62
View offer
Fertiligène Fertiligène Osmocote Max geranium fertiliser 700 g

Alternative

Fertiligène Fertiligène Osmocote Max geranium fertiliser 700 g
9.4/10about £23.00
View offer
Cultivers Cultivers organic geranium and flowering plant fertiliser 1 kg

Best value

Cultivers Cultivers organic geranium and flowering plant fertiliser 1 kg
8.8/10about £15.53
View offer
On this page
  1. 1.What you are feeding
  2. 2.Liquid 4-1-7, the 8-1-5 line, or the tub with no NPK
  3. 3.Pack size and the price per litre
  4. 4.Claims to leave on the label

What you are feeding

The plant most UK shops call a geranium is a pelargonium. The RHS keeps Geranium for hardy cranesbills and Pelargonium for tender plants. A cranesbill in ordinary soil usually needs no routine fertiliser. A pelargonium in a pot uses up the compost. If you are unsure, read pelargonium or hardy geranium before you spend about £12. Outdoor planting often waits until the end of May in much of the UK, and until early or mid June in Scotland.

Liquid 4-1-7, the 8-1-5 line, or the tub with no NPK

Cultivers liquids state NPK 4-1-7: 250 ml about £13.51, 1 litre about £15.86, 5 litres about £35.29, 10 litres about £54.59. No liquid prints a dilution. When to repeat a feed sits on how to feed geraniums. The 8-1-5 line states 74% organic matter. Only the 250 g listing, about £11.62, states granules. The 1 kg pack, about £15.53, and the 20 kg pack, about £60.42, do not. On 20 kg the bullets say 8-1-5 and one Spanish review says 8-7-5. Osmocote Max, 700 g at about £23.00, claims one year and 3 to 6 g per pot, with no NPK in the product data.
Cultivers Cultivers organic geranium and flowering plant fertiliser 250 g

Testsieger

Cultivers Cultivers organic geranium and flowering plant fertiliser 250 g
10.0/10about £11.62
View offer

Pack size and the price per litre

About £12 to £16 covers the 250 g, 250 ml, 1 kg and 1 litre packs. The 250 ml bottle is about £54 per litre. The 10 litre can is about £5.46 per litre at 12.5 kg. The 20 kg sack is about £3.02 per kilogramme. Three pots do not need 10 litres or 20 kg. The 1 kg pack costs about £4 more than the 250 g pack and holds four times the mass.

Claims to leave on the label

Organic, vegan and pet-safe lines are manufacturer or seller claims. No Cultivers listing names a UK organic certifier. Where the law says UK fertiliser, that is a route under the Fertilisers Regulations or assimilated Regulation (EC) No 2003/2003, not a flowering medal. Labels were not inspected. The 5 litre bullets say the liquid is harmless to animals. The pet question on the 250 ml page has no answer. If a child or a pet swallows concentrate, use NHS 111. This page gives no doses.

Common questions

Is 4-1-7 or 8-1-5 the one to buy?
Buy 4-1-7 liquid if you want the potassium-leaning ratio printed on the Cultivers bottles and you will repeat a feed. Buy the 8-1-5 line if you want the listing that prints more nitrogen, 74% organic matter, and humic acids. Neither ratio is an RHS recipe. Once flowers form, the RHS points pelargoniums to a high-potassium liquid such as a tomato feed. The 20 kg product data also contains a review saying 8-7-5, so do not treat 8-1-5 as settled on that sack.
Liquid or granules for a few pots?
A few pots suit the 250 ml liquid or the 250 g granules, not a 20 kg sack. Liquids are a habit you repeat. The 250 g listing is the only 8-1-5 ASIN that states granules. The Osmocote tub is granules with a printed 3 to 6 g pot dose, if you would rather feed once and you can accept that its NPK is not in the product data.
Why is 250 ml so expensive per litre?
The 250 ml bottle is about £13.51, about £54 per litre. The 1 litre bottle is about £15.86 for the whole litre, and the 10 litre can is about £5.46 per litre. You pay for a small pack you can finish. The saving on the large can is real only when you have enough baskets to use it.
Does organic on the title mean a UK scheme?
No certifier is named on these Cultivers listings. 100% organic, natural, and vegan origin stay as words on the amazon.co.uk page. They are not evidence of a UK organic scheme. The same limit applies to a bullet that says the 5 litre liquid is harmless to animals.
Can I pick the Osmocote tub for its NPK?
Not from this comparison. The product data for B09MSK5XVM has no N-P-K numbers. You can pick it for the gram dose, the February to June window, and the one-year claim, all of which are listing text. You cannot quote a ratio until the product data prints one.
Is a 20 kg bag sensible for a balcony?
No. At about £60.42 it is the cheapest per kilogramme, and it is still the wrong object for window boxes. Form is not stated, the star line is 3.2 from two reviews, and the NPK is in conflict between the listing and one Spanish review. A 250 g or 1 kg pack matches a balcony if you want the 8-1-5 line.
What must a GB fertiliser label show that Amazon bullets skip?
The RHS says a pack should declare the nutrients, the manufacturer, and the weight. Bullets often skip the full panel, the dilution, and whether phosphorus and potassium are oxides. Great Britain's UK fertiliser route is a legal designation, not a quality prize. We did not inspect the cartons behind these ASINs.

Related pages

Best geranium fertiliser

Geranium fertiliser

How to feed geraniums in spring, summer and winter

Pelargonium or hardy geranium: which plant to feed

Geranium fertiliser for pots, window boxes and baskets

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the eight amazon.co.uk listings captured on 19 October 2026. Organic, vegan and pet-safety lines are listing claims. The one-year granule line is the listing's claim, not a laboratory result. French, Spanish and Belgian reviews are not British comments.

  1. RHS, How to grow pelargoniums (retrieved 19 October 2026)
  2. RHS, How to grow geraniums (retrieved 19 October 2026)
  3. RHS, How to feed plants (retrieved 19 October 2026)
  4. RHS, Fertiliser labels explained (retrieved 19 October 2026)
  5. GOV.UK, Manufacturing and marketing fertilisers (retrieved 19 October 2026)
  6. legislation.gov.uk, Regulation (EC) No 2003/2003 Title I (retrieved 19 October 2026)
  7. RHS, Storing and disposing of chemicals safely (retrieved 19 October 2026)
  8. amazon.co.uk listings for the eight compared packs (retrieved 19 October 2026)