The 10°C Death Threshold

UNDERSTAND the cold kill point. Basil originates from tropical India and cannot survive below 10°C. When your greenhouse drops to 7°C overnight (common in May 2026), your basil experiences metabolic arrest.

Enzyme activity slows to 30% of normal. Cell membranes become rigid. Nutrient transport stops. The plant literally starves while appearing wilted.

ACT NOW before June. The ground soil is still only 8-12°C across most of the UK. Planting basil now guarantees failure.

The Misdiagnosis Crisis

STOP watering dying basil. The "wilted" appearance isn't drought—it's cold-induced stomatal closure. Your plant has closed its pores to conserve water because it can't move nutrients.

Most gardeners see wilted leaves and water more. This accelerates root rot in cold, wet soil. You're drowning a plant that's already dying from cold.

TEST your greenhouse temperature. Night-time greenhouse temps drop 3-5°C below outside air due to radiative cooling. Your 9°C outside night becomes 4°C inside.

The Real Solution

WAIT until June. The first week of June is the absolute earliest safe transplant date for basil in the UK.

Use horticultural fleece overnight until mid-June. Invest in a heated propagator (18-21°C soil temperature required). Accept that supermarket basil is a throwaway product, not a garden plant.