The frost lifts across much of Scotland. Harden off before you commit.

The month ahead

May is the month the frost lifts across much of Scotland ; but not all of it. Upland gardens and the north can still see frost into early June, so hold the tender crops back until you are confident your local last frost has passed. The soil is warm enough now for direct sowing of almost everything, and the long daylight hours mean growth is rapid once it starts.

Plant tomatoes into the greenhouse or polytunnel. Outdoors, wait until nights reliably stay above 10C ; a frost-free date is not enough; tomatoes need warmth, not just survival. Harden off every tender plant over one to two weeks before it goes outside permanently. Put up supports for peas and beans early, before they need them. Cover carrots, leeks and onions with fine insect-proof mesh now, before the pests arrive ; mesh goes on once and stays on.

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What to do in May

Sow indoors

Under cover: windowsill, heated propagator or greenhouse.

Sow outdoors

Direct into prepared ground (or under a cloche/fleece where noted).

Plant out

Move transplants, sets, tubers or cloves into their final spot.

Harvest

Ready to pick or lift this month (windows are approximate).

Fruit

Mulch around fruit bushes and canes while the soil is moist. A thick layer of compost or well-rotted manure now will hold moisture through summer and suppress weeds. Earth up potatoes consistently ; every time the shoots are 15cm high, draw soil up around them. The tubers must never see light. Plant summer-flowering bulbs like gladioli and lilies for colour through the season. Watch gooseberries and currants for sawfly larvae ; they can strip a bush in days, and picking them off by hand is more effective than any spray.

A long ridge of soil drawn up over a row of potato plants, with just the top leaves showing along the row
Every time the shoots reach 15cm, draw soil up around them. The tubers must never see light.

Key jobs in May

  • Plant tomatoes into the greenhouse or polytunnel; outdoors only once nights stay above 10C.
  • Plant out courgettes, beans and sweetcorn once your local last frost has passed.
  • Sow French and runner beans direct in milder areas.
  • Harden off all tender plants over 1–2 weeks before they go outside.
  • Succession-sow salad, carrots, beetroot and peas for continuous supply.
  • Put up supports for peas and beans early, before they need them.
  • Cover carrots, leeks and onions with fine insect-proof mesh.
  • Earth up potatoes and water consistently as growth surges.
  • Plant summer-flowering bulbs like gladioli and lilies for colour.
  • Mulch around fruit bushes and canes to hold moisture and suppress weeds.

The Scottish picture this month

The most generous growing conditions of spring, yet the north and uplands can still see frost into early June. Tender crops need hardening off and, in many gardens, the shelter of a wall or polytunnel.

Frost: Upland and northern gardens (Northeast, Borders, Highland and Central Belt uplands) reach their last-frost band mid-to-late May or early June, later than the lowlands.

Region-aware toolFrost Date CalculatorYour local last and first frost bands: the single most useful number for timing everything above.

Watch out for

Leek mothRHS UK timing · uncertain in Scotland

Two UK generations: May–June and a more numerous August–October flight. Mesh over alliums is again the practical control.

UK timing, and conditional in the same way as allium leaf miner; presence in Scotland is uncertain and local timing is unverified.

Carrot flyRHS UK timing · uncertain in Scotland

The avoidance model: sowing after mid-May dodges the first generation, and lifting before late August dodges the second. A 60cm fleece/mesh barrier helps whenever carrots are up.

The generation timing is the UK model; the Scottish calendar is not separately sourced. Use it as an avoidance strategy, not a dated forecast.

Mint rustbroad seasonal window

Symptoms can appear from spring until autumn. Cut affected mint to the ground and never propagate from infected plants.

Timing is broad, close to "the whole growing season", so treat it as a standing watch rather than a monthly alert.

These problems track the weather, not the calendar. Their month-by-month activity isn't sourced, so we tie them to the conditions that trigger them rather than pretend a date:

Slugs & snails

Watch when: mild, wet, damp conditions, worst around soft young growth

Activity tracks moisture and temperature, so risk climbs in any mild damp spell. Pressure is highest on tender seedlings in spring and again in a wet autumn.

Sources
  • RHS: grow-your-own guides: sowing, planting and harvest timing for all 25 crops (each window hand-derived from the crop's own RHS prose)
  • GrowScotland: pest activity framing: which pests to flag each month is our own reading of RHS activity data. We surface only what RHS sources, and frame weather-driven diseases by trigger conditions rather than inventing a Scottish calendar