What percentage shade cloth should I use in a UK greenhouse?

For a mixed UK greenhouse, 40-50% is the usual all-round choice. Heat-loving fruiting crops (tomatoes, peppers, aubergines) prefer a lighter 30-40% so they still ripen, while cool leafy salads such as lettuce want 50-70% in midsummer to stop bolting. Seedlings, ferns and orchids being propagated like 60-70%. The shade percentage is the fraction of light the cloth blocks, so 50% cloth lets through half the light.

How much shade cloth do I need to cover my greenhouse?

The usual install drapes one sheet over the ridge so it covers the whole roof and hangs about two-thirds of the way down both long side walls, where the strongest sun strikes. This calculator sizes that single sheet: the length runs the full greenhouse length and the width spans the roof plus the drape down each side, with a 30 cm overlap added on every edge for fixing. Buy to the next standard roll size up.

If I put two layers of shade cloth together, do the percentages add up?

No — they multiply, not add. Two 50% nets do NOT give 100% shade. Each net passes 50% of the light, so two together pass 0.5 × 0.5 = 25%, which is 75% total shade. The formula is combined shade = 1 − (1 − s₁)(1 − s₂). Enter an existing layer under Advanced Options and the calculator shows the real combined figure, so you do not accidentally plunge the crop into deep shade.

Should the shade cloth go inside or outside the greenhouse?

Outside is far more effective because it stops the sun before it heats the glass and the air inside. External cloth can cut greenhouse temperatures by several degrees more than internal shading. Internal cloth or blinds are easier to fit and adjust but mainly protect leaves from scorch rather than controlling heat. Either way, leave vents clear so air can still move.

When should I put greenhouse shade cloth up and take it down?

In most of England and Wales, shading goes up from late May or June and comes off in September as light levels drop. Southern England usually needs it earlier than Scotland. Take it down promptly in autumn — shade that stays on too long cuts the light fruiting crops need to finish ripening. Good cloth lasts several seasons if folded and stored dry.

Shade Coverage Calculator — Greenhouse Shade Cloth

How We Calculate This

The calculator does two jobs: it sizes the sheet of shade cloth (netting) you need to buy, and it recommends the shade density for your crop.

Cloth area: One sheet is draped over the ridge to cover the whole roof and hang two-thirds of the way down both side walls. Sheet length = greenhouse length, sheet width = greenhouse width + 2 × (two-thirds of the eaves height), and a 30 cm overlap is added on every edge for clipping or weighting down. Area = length × width.

Shade percentage: The shade % is the share of light the cloth blocks. Defaults follow UK grower guidance — 40-50% general, 30-40% tomatoes/peppers, 50-70% leafy salads, 60-70% propagation.

Two layers multiply: If you already have a net up, the combined shade is 1 − (1 − s₁)(1 − s₂), not the sum. Two 50% nets give 75% shade, not 100%. Enter an existing layer under Advanced Options to see the real combined figure.

Frequently Asked Questions

Related Calculators

Greenhouse Size Calculator

Work out the ideal greenhouse size for your growing plans.

Cold Frame Calculator

Calculate cold frame size and capacity for hardening off plants.

Grow Light Calculator

Work out grow light wattage and coverage for indoor growing.

Seed Starting Calculator

Calculate seed quantities with germination rates and succession sowing.

Propagation Calculator

Work out propagator capacity and timing for cuttings and seeds.

Last updated: June 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.