When to plant watermelons in Jeju City: 6 May – 9 September

In Jeju City, watermelon: sow for seedlings from 18 March to 12 August; plant into a greenhouse from 15 April to 9 September; plant out into open ground from 6 May to 9 September.

Watermelon in Jeju City: soil, season and weather

In Jeju City the soil, not frost, sets the date: the last frost is over around 18 February, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 6 May, 77 days later.

Last spring frost	18 February
Top 7 cm of soil at 18 °C	6 May, 77 days after the last frost
Into an unheated greenhouse	15 April – 9 September; April outside: 11.4 °C at night, 17.6 °C by day; card 18–35 °C
First autumn frost	19 December, 227 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	4 July – 7 November
Days left for picking	168
Daylight	12:46 on 8 April, 13:39 on 6 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, December, has 14 rainy days

The same dates in Jeju City hold for Cucumber, Bell Pepper, Eggplant, Zucchini and Pumpkin.

Watermelon in Jeju City: care after planting

Planted on 6 May: in the first weeks water every 5 days.

Feeding, by the card’s schedule from that day:

6 May — feed: balanced (NPK)

Pests and diseases of watermelon to watch for:

Dates count from the first planting day of the window above; a later planting moves them by as many days.

Weather in Jeju City during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, August, averages 29.9 °C. Months that stay below 18 °C even by day on average: November (15.7 °C) and December (9.9 °C). Nights average below 18 °C in May and October–December (5.2–16.4 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	21.8	15.7	148	11	13:53
June	25	19.9	208	14	14:22
July	29	24.6	233	18	14:10
August	29.9	25.4	240	19	13:25
September	26.1	22	354	19	12:25
October	20.8	16.4	182	13	11:23
November	15.7	10.4	108	11	10:27
December	9.9	5.2	85	14	9:57

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

All the nearest cities on our list plant watermelon later than Jeju City; the closest date is in Busan, 9 days later.

City	Distance	Date	Difference
Gwangju	187 km	17 May – 14 August	11 days later
Jeonju	263 km	19 May – 8 August	13 days later
Busan	299 km	15 May – 13 August	9 days later
Daegu	324 km	16 May – 12 August	10 days later
Daejeon	326 km	17 May – 3 August	11 days later
Ulsan	342 km	18 May – 7 August	12 days later

Where to buy watermelon plants and seeds near Jeju City

Buy plants ready to set out from 6 May to 9 September (from 15 April to 9 September for an unheated greenhouse); seed for raising your own is sown from 18 March to 12 August. Within 15 km of Jeju City OpenStreetMap lists 1 garden centre, 7 markets and 1 farm shop (collected 28 October 2026).

함덕오일시장 — market
14 km
화북종합시장 — market
5 km
제주 탐나봉 — farm shop
1 km
Well Being Wonye Mart — garden centre
3 km

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.

Questions