How Often Should You Feed Tomatoes? A Week-by-Week Guide

The most common feeding mistakes UK gardeners make with tomatoes are feeding too early, feeding too often during vegetative growth, and stopping too soon at the end of the season. This week-by-week guide shows exactly when to start, how often to feed, and when to stop — for both greenhouse and outdoor growing.

The Key Principle

Tomato plants don't need high-potash feed during vegetative growth — when they are just producing leaves. The potassium hits its highest demand from the moment the plant starts setting fruit. Feeding too early wastes nutrients the plant can't use; feeding too late means the fruit never reaches full size or flavour.

The trigger to start is the same regardless of variety or growing method: start feeding once the second flower truss has set fruit. Until then, the plant is best served by the nutrients already in good potting compost or well-prepared soil.

Greenhouse & Container Tomatoes — Week by Week

This schedule assumes plants are transplanted into final pots, grow bags, or borders in late April to early May in the UK.

Outdoor & Allotment Tomatoes — Week by Week

Outdoor tomatoes typically grow more slowly than greenhouse plants and don't dry out as fast. The schedule is similar but the frequency is slightly lower.

How Much Diluted Feed Per Plant?

The dilution rate stays the same — 15ml per 4.5L of water — but the volume applied per plant depends on the plant size and the growing container.

• Young plants (first 2–3 feeds): 0.5L of diluted feed per plant.
• Established plants in grow bags: 0.5–1L per plant, typically 2L of feed for a standard 2-plant grow bag.
• Large container plants (15L+ pots): 1L per plant.
• Border-grown plants in greenhouse: Apply slowly to soak the root zone — typically 1–1.5L per plant.

Common Feeding Mistakes

• Feeding before the second truss has set fruit. Wastes potassium the plant can't use. Excess nitrogen at this stage actively reduces fruiting.
• Feeding at higher than the recommended rate. Excess potassium interferes with calcium and magnesium uptake — the main cause of blossom end rot.
• Skipping feeds during a heatwave. Plants drying out fast need more, not fewer, feeds. Increase to twice weekly in extreme heat.
• Feeding on dry soil. Always water normally first, then apply diluted feed. Concentrated feed on dry roots can scorch.
• Stopping too early in September. Late-season trusses still ripening benefit from continued feeding until cool weather slows the plant down.
• Mixing more than you'll use in one day. Diluted feed is best applied fresh. Don't store mixed solution for later use.

Indeterminate (Cordon) vs Determinate (Bush) Tomatoes

The feeding schedule is essentially identical between varieties. The difference is duration:

• Cordon (indeterminate) varieties like Sungold and Gardener's Delight keep producing fruit through the season — feed weekly until late September.
• Bush (determinate) varieties like Tumbler and Roma produce most fruit in a shorter window — feed weekly until the last truss has begun ripening, then taper off.