Reading a five-day forecast

A five-day weather forecast is accurate enough to make decisions. Beyond five days, confidence drops sharply — which is fine, because most garden tasks need only a few days' notice. The mistake is reading a forecast for information rather than for action. You do not need to know whether it will rain next Thursday. You need to know whether to water tonight, whether to delay sowing until the weekend, whether to harvest beetroot tomorrow before three days of rain rot them in the ground.

Look for overnight lows, not daytime highs. A forecast of 18°C and sunny tells you nothing useful. A forecast of 18°C by day, 4°C overnight, tells you everything: wait three more days before planting out peppers, because cold nights stall growth even if days are warm. Similarly, a forecast of rain is less important than knowing whether it is 8mm (useful) or 40mm (destructive). Most apps now show predicted rainfall in millimetres — anything above 25mm in 24 hours will flatten seedlings and drown pots without drainage.

Wind is the forgotten element. A dry day with 40km/h gusts will desiccate transplants faster than a hot day with no wind. If strong wind is forecast, delay planting out or stake anything tall and newly planted. Wind also lowers the effective temperature — a still night at 5°C is survivable for half-hardy plants; a windy night at 5°C is a frost in disguise.