The main harvest month: pick, store and sow the last quick crops.
The month ahead
August is the main harvest month, and it is also when the season begins to turn, particularly in the north. The days are still warm but the nights are lengthening, and the earliest autumn frosts are only weeks away in upland gardens. The focus is on storing the harvest, clearing spent crops, and getting the last quick sowings in for autumn and winter.
Harvest and dry maincrop onions and garlic once the tops flop over and turn brown. Leave them on the soil surface for a few dry days if you can, then bring them under cover to finish drying. Lift maincrop potatoes and store undamaged tubers in hessian or paper sacks in complete darkness ; light turns them green and toxic. Keep picking beans, courgettes and tomatoes to prolong cropping. Sow fast autumn and winter salads, spinach and oriental leaves under cover for picking into winter.
What to do in August
Sow indoors
Under cover: windowsill, heated propagator or greenhouse.
None of our 25 crops is typically started under cover this month.
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
Plant new strawberry runners so they establish before the cold arrives. Prune summer-fruiting raspberries: cut the canes that fruited right down to the ground and tie in the new green canes for next year. Order autumn onion sets and garlic now ; the best varieties sell out early. Collect and dry seed from this year's best plants. Cut back finished herbaceous perennials that are looking tatty.
Key jobs in August
- Harvest and dry maincrop onions and garlic once the tops flop over.
- Lift maincrop potatoes and store undamaged tubers in hessian sacks in the dark.
- Keep picking beans, courgettes and tomatoes to prolong cropping.
- Sow fast autumn and winter salads, spinach and oriental leaves under cover.
- Plant new strawberry runners so they establish before winter.
- Prune summer-fruiting raspberries: cut fruited canes to the ground, tie in new ones.
- Order autumn onion sets and garlic for planting next month.
- Collect and dry seed from this year's best plants for next season.
- Cut back finished herbaceous perennials that are looking tatty.
- Start clearing spent crops: compost healthy material, bin blighted foliage.
The Scottish picture this month
Still warm but the first hints of autumn appear, particularly in the north. Wet, humid weather keeps blight, mildew and leek rust in play. Nights slowly lengthen.
Frost: Frost-free across the country, though the earliest upland/northern first-frost bands are now only weeks away (mid-to-late September).
Region-aware toolFrost Date CalculatorYour local last and first frost bands: the single most useful number for timing everything above.Watch out for
Vine weevil (adults)
Adults notch leaf edges through summer. The adult stage is recorded as a summer season rather than exact months.
Allium leaf minerRHS UK timing · uncertain in Scotland
Two egg-laying periods on alliums: March–April and late summer–autumn. Covering leeks, onions and garlic with fine mesh over those windows is the main defence.
UK timing, and conditional: the pest may not be established across all of Scotland, and where it is, Scottish generations have consistently lagged the UK ones. Treat these as a UK guide, not a Scottish forecast.
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:
Potato & tomato blight
Watch when: warm, humid, muggy spells in the main growing season
June onwards for the UK; Scottish onset not separately sourced, so we tie it to the weather. Watch potatoes and outdoor tomatoes after warm, wet spells.
Grey mould (botrytis)
Watch when: cool, damp, still air, especially under cover
Can occur year-round with latent infections; ventilation and airflow are the real controls. Peaks when growth is soft and air is stagnant.
Powdery mildew
Watch when: dry spells and drought stress at the roots
Driven by dry, warm weather and plants short of water. Keep roots watered and airflow open around courgettes and peas.
Leek rust
Watch when: warm, wet summers with poor airflow
A wet-summer disease that is genuinely more of a Scottish problem than the allium insects. Space alliums generously; driven by leaf wetness, not a date.
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