Best fertiliser for tomatoes UK — Tomorite & more

Best fertiliser for tomatoes UK — Tomorite and the alternatives

Walk down the garden aisle at B&Q, Dobbies, or Notcutts and you will see 20-plus products claiming to be "the best for UK tomatoes." The truth: most of them work. The difference between them is application convenience, organic vs synthetic, the size of your watering can, and your starting soil — not whether the tomatoes will grow. The single dominant UK product is Tomorite (the Levington / Westland brand has owned the British tomato-feed market for decades), and it is genuinely good — but it is not the only good option, and depending on your setup a granular slow-release like Vitax Q4 or a high-K crystal feed like Chempak Tomato Food may suit you better. The same high-potassium rhythm applies if you are also growing peppers the UK way or keeping a pot of British-grown basil as a companion crop.

This guide cuts the noise: which NPK ratio at which stage, with specific UK-stocked product names that work, and an honest look at when organic vs synthetic actually matters in a British garden.

Skip the guessing: Add your tomato variety and growing setup (greenhouse, polytunnel, growbag, allotment bed, patio container) to Growli and the app recommends a specific UK-stocked product, dilution rate, and application frequency based on your stage of growth and local conditions.

The NPK rule for UK tomatoes

Tomatoes need different nutrient ratios at different stages of British growth. The British growing season is shorter and cooler than the US one, which makes the stage-specific feed switch slightly more time-sensitive than in warmer climates.

N (nitrogen) drives leafy green growth. P (phosphorus) drives root and flower development. K (potassium) drives fruit set and ripening. Too much N produces leafy plants with few tomatoes — the single most common UK fertiliser mistake, particularly with allotment gardeners who use general-purpose Growmore or fish-blood-bone fertiliser straight through the season.

The UK greenhouse and growbag-dominant context matters too: container tomatoes have zero soil reserves and need higher-frequency feeding than in-ground plants, while peat-free growbag compost (the British standard) is generally pre-charged with 8-12 weeks of nutrient before you need to start feeding at all.

Specific UK products that work

Liquid concentrates (the British default)

Granular slow-release (allotment and raised bed)

Organic and natural options

Tomorite — why the UK default is genuinely good

Levington Tomorite has dominated the UK tomato-feed market for so long that many British gardeners have never used anything else. The reasons it works:

• NPK of 4-3-8 hits the right K-heavy ratio for fruiting tomatoes without overwhelming the plant with the very high K (30%+) of Chempak.
• Magnesium and seaweed extract included — magnesium prevents the yellow-between-veins interveinal chlorosis common in UK tomatoes, and seaweed extract feeds soil biology and provides trace minerals.
• Dilution is forgiving — the 10 ml per 1.5 L recommended rate is hard to over-apply, unlike Chempak crystals which can scorch roots if measured carelessly.
• Widely stocked at every UK garden centre — B&Q, Wickes, Dobbies, Notcutts, British Garden Centres, Wilko (when it existed, now closed), Amazon UK, and most supermarkets in spring/summer.

The honest weakness: at high yields under polytunnel cover with heavy-cropping varieties, Tomorite's relatively moderate K can become limiting in the final 6 weeks of the season — that is when serious UK growers switch to Chempak or Westland Big Tom. For most allotment and patio growers it remains the right product.

Organic vs synthetic — which works better in the UK?

Both work. The honest UK trade-offs:

• Synthetic (Tomorite, Chempak, Westland) acts fast (days), is precise on NPK, and is easier to over-apply and burn roots. Best for container and growbag tomatoes where the compost has no living soil to convert organic matter.
• Organic (Maxicrop, Vitax Organic, comfrey tea, worm castings) acts slow (1-3 weeks), feeds the soil biology, is much harder to burn plants with, but needs higher application frequency. Best for in-ground allotment beds and raised beds where you are building soil fertility year over year.

For UK container and growbag tomatoes (the dominant British setup), synthetic Tomorite is usually easier — growbag compost is a sterile peat-free or peat-reduced mix with no living microbiome to convert organic feed. For UK allotment beds, organic is preferable long-term because it builds soil fertility and structure.

Natural and homemade UK options

Three that genuinely work in British conditions:

1. Comfrey tea — the UK allotment classic. Cut comfrey leaves (Symphytum officinale or 'Bocking 14'), pack into a bucket with a lid, weigh down with a stone, leave 4-6 weeks. The resulting black smelly liquid is roughly 1-0-4 NPK. Dilute 15:1 with water and apply weekly during fruiting. Free if you grow comfrey.
2. Worm castings — mix 2 handfuls into the planting hole and top-dress monthly. Gentle, slow-release, near-impossible to over-apply. Available from UK wormeries (Wiggly Wigglers, Original Organics) or your own worm bin.
3. Nettle tea — same method as comfrey but with stinging nettles. Higher in N than comfrey (roughly 4-1-2) — use early in the season for leafy growth, then switch to comfrey or Tomorite at flowering.

Things UK gardeners try that do not work well: coffee grounds (too acidic in quantity, also a slug attractant in damp British conditions), banana peels (potassium is there but takes weeks to break down), and Epsom salt as a "fertiliser" — it is a magnesium supplement, not a fertiliser, useful as a one-off drench for interveinal chlorosis but not a standalone feed.

When to switch products

Do not switch products mid-season unless something is going wrong. Consistency matters more than choosing the "best" product. The two UK reasons to switch:

1. Lots of leafy growth, few flowers. Drop the nitrogen. Switch from a balanced feed to Tomorite or a higher-K organic. Common UK problem when allotment gardeners use Growmore (7-7-7) straight through the season.
2. Yellowing leaves with green veins despite regular feeding. Magnesium deficiency — the classic interveinal chlorosis pattern. Add 1 tablespoon Epsom salts per 4 L of water as a one-off drench. Does not replace your regular feed.

UK feeding schedule by setup

Greenhouse or polytunnel tomatoes (the British standard)

• Weeks 1-3 after transplant: no feed; let establish in fresh growbag/compost
• Weeks 4-6: Tomorite at half rate every 10-14 days
• Week 7 to first ripe fruit: Tomorite at full rate every 7 days
• Final fortnight before final harvest: stop feeding

Outdoor patio container tomatoes

• Same schedule but start full-rate Tomorite 1 week earlier — outdoor UK conditions are more variable and the plant uses nutrients faster in heatwaves
• Add seaweed extract weekly during fruiting for trace minerals

Allotment or raised bed in-ground

• Mix Vitax Q4 granular into the planting hole at transplant
• Side-dress with another handful of Q4 at first flower
• Liquid feed (Tomorite or comfrey tea) every 10-14 days through fruiting
• Stop 2 weeks before final harvest

Related articles

• How to grow tomatoes — UK guide — full growing guide for British gardeners
• When to plant tomatoes — UK guide — timing windows by UK region
• How to grow peppers — UK guide — same high-K feed rhythm applies
• Why are my plant leaves turning yellow? UK guide — magnesium deficiency variant
• Seed starting indoors UK — the 6-8 week head start tomatoes need
• UK RHS hardiness ratings explained — for timing the feed-stop and harvest dates
• Frost date calculator — for planning the UK tomato season

Reviewed and updated by the Growli editorial team. For questions about anything here, open Growli and ask — or email hello@getgrowli.app.