What to Do in the Garden in May (UK)

Sow and plant

• Harden off young plants for 10–14 days before planting out, waiting until night temperatures no longer dip below around 7°C.
• Plant out tomatoes, courgettes and pumpkins raised under cover once all risk of frost has passed.
• Direct sow French beans, runner beans, squash, cucumbers and pumpkin seeds into prepared beds outside.
• Sow sweetcorn outside in blocks at 45cm spacing, two seeds per hole, to aid wind pollination.

Prune and tidy

• Give the Chelsea chop (usually at the end of May, around the RHS Chelsea Flower Show) to perennials such as sedums, asters, echinaceas, rudbeckias, heleniums and phlox — cut flower stems back by up to half for compact growth and later flowers.
• Stay on top of weeding while weeds are small and soft.

Watering and general care

• Keep freshly sown seed and young vegetable plants consistently moist.
• Sink a 15cm pot into the ground beside tomatoes and water into it so water reaches the roots directly; thirsty crops such as courgettes and tomatoes suit drip irrigation.

Regional adjustment

The RHS keys May planting-out to your local last frost, not a fixed date: in most parts of the country you can harden off and plant out this month, but last frosts fall later in colder northern gardens and earlier in the milder south and west, so let night temperatures — not the calendar — decide.

Sources

Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.

• RHS — Gardening in May: jobs to do this month — May monthly jobs including hardening off over about 10–14 days and planting out once nights stay above around 7°C.
• RHS — Grow Your Own: jobs to do in May — Plant out tomatoes, courgettes and pumpkins after frost risk passes; direct sow French and runner beans, squash, cucumbers and pumpkins; sow sweetcorn in blocks at 45cm spacing; watering guidance for young crops.
• RHS — The Chelsea chop — Chelsea chop is done around late May; cut stems back by up to half on perennials such as sedums, asters, echinaceas, rudbeckias, heleniums and phlox.
• RHS — When to plant out tender plants to avoid frosts — Planting-out timing depends on local last frost dates, which vary across the UK.

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