Still Time to Sow in August?

The Short Answer

Yes, several crops still have time after 15 August, but not because "it's still summer" — because the maths works out. Rocket and radish are the quickest. Spinach and spring onions aren't far behind. Turnips and winter lettuce round out the list. All six are still on GardenCalc's own August sowing list, drawn from the same planting calendar that sits behind our interactive planting calendar.

What decides it isn't the calendar month. It's whether the crop's weeks to harvest fit inside the weeks you have left before your first autumn frost. A crop that takes 4 weeks has a completely different late-summer deadline to one that takes 10. Get that comparison right and "is it too late" stops being a guess.

The Maths: Count Back From Your Frost Date

UK first frost dates vary far more by region than most sowing advice admits. Per Met Office HadUK-Grid 5km gridded observations (1991–2020), the first autumn frost typically arrives:

• Late October in the Scottish Highlands
• Mid-November to early December across most of England and Wales
• December or later in mild south-western coastal areas such as Cornwall

That is a real spread of ten weeks or more between regions, sown from the same date. Counting forward from 15 August:

Those week counts are simple calendar arithmetic from the published frost ranges above, not a promise for your specific garden. Frost dates are a distribution, not a fixed line, and local factors — a frost pocket, a valley bottom, an exposed plot — shift the real date further. For your postcode's actual estimate, use the frost date calculator, which is built from the same Met Office dataset and covers 2,728 UK postcode districts.

What Still Fits After 15 August

Cross-referencing each crop's typical time to harvest against the frost windows above:

Source for the sowing windows and harvest times: GardenCalc's planting calendar, which lists month-by-month sow/plant/harvest data for each of these crops, cross-checked against the Royal Horticultural Society's grow-your-own vegetable guides.

What's Genuinely Too Late

The blanket "too late to sow" advice is wrong for the fast crops above, but it's right for the slow ones. From seed, in mid-August, these are past their window almost everywhere in the UK:

• Outdoor tomatoes — need to be planted out after the last frost in spring to ripen before autumn cold
• Sweetcorn — needs a full summer of heat; a mid-August sowing won't cob before frost
• Runner beans — needs around 12 weeks from sowing and, critically, warm soil and warm nights to germinate and set pods reliably; a mid-August sowing runs into declining temperatures long before frost arrives, and the flowers that do open won't set in cool evenings
• Maincrop potatoes — planted from seed potatoes in spring, not sown from seed in summer at all

These aren't "maybe if you're lucky" crops. They need the growing season that's already passed, not the one that's left.

Two Things That Cost More Yield Than the Date Does

Spacing

Warm August soil germinates fast, which makes it easy to sow too thickly out of habit from cooler spring sowings. Thin seedlings promptly once they're large enough to handle, following the spacing on the seed packet — crowded rows of any of the crops above will bolt or stay undersized rather than filling out properly.

Slug pressure

Late-summer soil stays warm and often damp, which is exactly the condition slugs favour, and young seedlings are their easiest target. Protect new sowings from day one with copper tape, wildlife-friendly slug pellets, or a physical barrier such as a cloche, rather than waiting to see if it becomes a problem. Winter lettuce and spinach seedlings are particularly vulnerable while small.

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