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How to use tomato fertiliser without doubling the dose

Updated: October 2026

Knowing how to use tomato fertiliser starts with timing, not the cap. Seedlings and newly planted tomatoes do not need an immediate high-potassium feed. Wait until fruit begins to set at the stage on your label, water the compost, then measure the correct product dose. A concentrate goes into a watering can; a ready-mixed bottle does not. Our [tomato fertiliser comparison](/hub/fertiliser-soil-and-bark-mulch/tomato-fertiliser) distinguishes those formats. The bottle in your hand takes priority, because marketplace fields can be incomplete. Products Compared did not run a feeding trial. A qualifying purchase can earn us a commission at no extra cost to you.

Knowing how to use tomato fertiliser starts with timing, not the cap. Seedlings and newly planted tomatoes do not need an immediate high-potassium feed.

Our top picks

Doff Doff Tomato Feed 1 L

Best overall

Doff Doff Tomato Feed 1 L
9.2/10about £5.30
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Doff Doff Tomato Feed 2.5 L

Preis-Tipp

Doff Doff Tomato Feed 2.5 L
8.8/10about £12.18
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Doff Doff Tomato Pour and Feed 3 L

Alternative

Doff Doff Tomato Pour and Feed 3 L
7.8/10about £6.53
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On this page
  1. 1.When the first feed is due
  2. 2.How much goes into the watering can
  3. 3.Where to pour and how often
  4. 4.Mix only what you will use

When the first feed is due

Do not feed tomato seedlings with a fruiting feed to make them grow faster. Enriched compost usually contains nutrients for the establishment period. Levington says not to feed before two weeks after planting, while mainstream UK guidance starts high-potassium feeding once flowers have formed and fruit is beginning to set. Levington guidance starts greenhouse feeding from the first truss of small green fruits and outdoor feeding later. RHS guidance for containers is a high-potassium liquid every 10–14 days once the first fruits swell. These are not instructions to combine. More frequent watering does not mean every watering should contain feed. Soil enriched with compost or manure may already hold enough for ground-grown plants. If you are still choosing a format, use the tomato fertiliser buying guide.

How much goes into the watering can

First identify whether you have a concentrate. Levington's published Tomorite direction for tomatoes is 20 ml in 4.5 litres of water. Measure 20 ml, add it to the can and make the solution up to 4.5 litres. Do not use an unmarked cup, and do not assume every brand uses the Tomorite rate. Doff Pour and Feed is already mixed. Doff's page describes 100 ml at the base after watering, while the captured Amazon extract says 2.5 caps every 4–7 days. Use the pack you received. Pouring that bottle into 4.5 litres changes the intended application. The Tomorite twin pack has a marketplace field of 1:10, which conflicts with 20 ml in 4.5 litres. PowerGrow extracts in this comparison give no numeric rate. Never invent a dose from bottle size, NPK or another crop. Peppers and aubergines can have a different label rate even when one bottle names all three. If the instructions are unreadable, contact the manufacturer with the product and batch rather than guessing.
Doff Doff Tomato Feed 1 L

Testsieger

Doff Doff Tomato Feed 1 L
9.2/10about £5.30
View offer

Where to pour and how often

Water the root zone, not the leaves. If the compost is dry, give plain water first. Pour steadily around the base so the dose does not run down one channel. Containers can need daily water in a hot greenhouse, and that is not a daily feed. The RHS links blossom end rot with calcium movement disrupted by moisture fluctuation. A stronger feed does not repair a black, sunken end. If that is what you see, use the tomato blossom end rot guide rather than doubling the dose.

Mix only what you will use

Make up only the amount for that session. The RHS advises against storing diluted garden chemicals. A part-filled can can be mistaken for plain water. Keep the closed bottle in its labelled container, not a drinks bottle, and not beside food. The Topline listing includes a separate pest spray. Do not mix that spray into the watering can. If the label does not authorise the use, stop. To replace an unclear or leaking bottle, the best tomato feed UK guide matches packs to plant numbers. A leak is a product fault, not a reason to pour the contents into an unlabelled container.

Common questions

When should I start feeding greenhouse tomatoes?
Begin at the fruiting stage stated on your label. Levington guidance starts greenhouse feeding when the first small green fruits appear on the first truss. Do not use tomato feed on seedlings or automatically begin on planting day.
How often should I feed tomatoes in a grow bag?
Follow the product schedule. UK guidance ranges from weekly to twice weekly under glass for some programmes, while RHS container guidance gives every 10–14 days once fruit swells. Plain watering may be needed much more often.
How much Tomorite goes into 4.5 litres?
Levington's published tomato rate is 20 ml in 4.5 litres of water. Confirm that rate on your current bottle, because pack directions can change and other crops or products may use a different measure.
Do I dilute Doff Pour and Feed?
No. It is sold as ready to use. Apply the amount printed on your bottle at the base after watering. Do not treat its three-litre pack as three litres of concentrate.
Can I save leftover diluted feed?
Do not plan to store it. Mix only what you can use at the current feeding, and keep the concentrate closed in its original labelled bottle. A stored watering can creates identification and access risks.
What should I do if my bottle says 1:10?
Check the full pack directions and product identity rather than relying on one marketplace field. The Tomorite twin-pack listing contains 1:10, but Levington's published tomato rate is 20 ml in 4.5 litres. Contact the manufacturer if the label remains unclear.

Related pages

Tomato soil compared

Tomato fertiliser

Best tomato feed UK: the right bottle for your plants

Tomato blossom end rot: fertiliser is not the first fix

Tomato fertiliser buying guide: checks before you pay

Organic or standard tomato feed: what the label proves

Sources

Public UK and manufacturer sources used for this comparison; last accessed 15 October 2026.

  1. RHS: Tomatoes, grow your own (retrieved 15 October 2026)
  2. RHS: Blossom end rot (retrieved 15 October 2026)
  3. RHS: Storing and disposing of garden chemicals safely (retrieved 15 October 2026)
  4. GOV.UK: Manufacturing and marketing fertilisers (retrieved 15 October 2026)
  5. GOV.UK: Product regulations and UKCA and CE marking (retrieved 15 October 2026)
  6. HSE: Using pesticides in the garden and home (retrieved 15 October 2026)
  7. Levington Tomorite concentrated tomato food (retrieved 15 October 2026)
  8. Doff tomato feed concentrate (retrieved 15 October 2026)