Last and first frost dates in Jeju City

When is the last frost in Jeju City?

The last frost in Jeju City usually comes around 18 February: that is the median of 2016–2025, so in about half of those years the last night at or below 0 °C came later. Hardy crops start before it and frost-tender ones only after it: in the table below arugula can go into open ground from 28 January, while corn waits until 21 March. The first autumn frost follows around 19 December, about 304 days later: harvest or cover frost-tender crops before then.

When to sow and plant

Planting out: a week after the last frost once the soil is warm enough for the crop; frost-hardy crops three weeks before it; an unheated greenhouse three weeks earlier. Seedlings are sown so they are ready on that day. Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.

When the soil warms up in Jeju City

The day the top 7 cm of soil first averages each temperature over a week, median of 2016–2025 (ERA5 via Open-Meteo). The soil reaches 10 °C 17 days after the last spring frost and 15 °C 52 days after it.

Frost dates near Jeju City

Of the nearest cities on our list, the last spring frost ends earliest in Busan (19 March) and latest in Daejeon (1 April).

Weather in Jeju City by month

Average weather in Jeju City over 2016–2025: the warmest month is August. Months that average 20 °C or more by day: May–October (20.8–29.9 °C). No month averages below 0 °C at night; the coldest nights, in January, average 3.2 °C. About 2020 mm of rain falls in a year, on 165 days; September is the wettest month (354 mm) and December the driest (85 mm).

Average of the daily highs and lows, rain per month and days with at least 1 mm (ERA5 via Open-Meteo, the same grid cell as the frost dates).

Planted in autumn

From a month before the first autumn frost, so the roots grow before winter, to the late-planting limit on each crop’s page (about two weeks before the ground freezes, by ten years of weather).