When to plant watermelons in Ulsan: 18 May – 7 August

In Ulsan, watermelon: sow for seedlings from 30 March to 10 July; plant into a greenhouse from 27 April to 7 August; plant out into open ground from 18 May to 7 August.

Watermelon in Ulsan: soil, season and weather

In Ulsan the soil, not frost, sets the date: the last frost is over around 22 March, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 18 May, 57 days later.

Last spring frost	22 March
Top 7 cm of soil at 18 °C	18 May, 57 days after the last frost
Into an unheated greenhouse	27 April – 7 August; April outside: 7.8 °C at night, 18.1 °C by day; card 18–35 °C
First autumn frost	16 November, 182 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	16 July – 5 October
Days left for picking	123
Daylight	13:15 on 20 April, 14:06 on 18 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, November, has 4 rainy days

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

Watermelon in Ulsan: care after planting

Planted on 18 May: in the first weeks water every 5 days.

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

18 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 Ulsan during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, August, averages 29.7 °C. Months that stay below 18 °C even by day on average: November (14.7 °C). Nights average below 18 °C in May, June and October, November (4.3–17.4 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	22.6	12.5	112	9	14:02
June	25.9	17.4	180	11	14:33
July	28.9	22.3	266	16	14:21
August	29.7	22.9	216	16	13:32
September	25	18.6	268	16	12:26
October	20	11.8	120	9	11:20
November	14.7	4.3	37	4	10:19

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Ulsan, Busan is 3 days earlier and Jeonju 1 day later.

City	Distance	Date	Difference
Busan	47 km	15 May – 13 August	3 days earlier
Daegu	74 km	16 May – 12 August	2 days earlier
Daejeon	195 km	17 May – 3 August	1 day earlier
Jeonju	198 km	19 May – 8 August	1 day later
Gwangju	228 km	17 May – 14 August	1 day earlier
Kitakyushu	234 km	from 15 May	3 days earlier

Where to buy watermelon plants and seeds near Ulsan

Buy plants ready to set out from 18 May to 7 August (from 27 April to 7 August for an unheated greenhouse); seed for raising your own is sown from 30 March to 10 July. Within 15 km of Ulsan OpenStreetMap lists 1 garden centre, 8 markets and 1 farm shop (collected 28 October 2026).

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.

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