When to plant watermelons in Kumamoto: 2 May – 24 August

In Kumamoto, watermelon: sow for seedlings from 14 March to 27 July; plant into a greenhouse from 11 April to 24 August; plant out into open ground from 2 May to 24 August.

Watermelon in Kumamoto: soil, season and weather

In Kumamoto the soil, not frost, sets the date: the last frost is over around 18 March, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 2 May, 45 days later.

Last spring frost	18 March
Top 7 cm of soil at 18 °C	2 May, 45 days after the last frost
Into an unheated greenhouse	11 April – 24 August; April outside: 10.4 °C at night, 20.6 °C by day; card 18–35 °C
First autumn frost	3 December, 215 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	30 June – 22 October
Days left for picking	156
Daylight	12:37 on 4 April, 13:30 on 2 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, December, has 9 rainy days

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

Watermelon in Kumamoto: care after planting

Planted on 2 May: in the first weeks water every 5 days.

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

2 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 Kumamoto during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, August, averages 32.3 °C. Months that stay below 18 °C even by day on average: December (12.4 °C). Nights average below 18 °C in May and October–December (2.9–14.8 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	24.3	14.6	255	14	13:50
June	27.2	19.3	442	18	14:18
July	30.8	23.4	381	19	14:07
August	32.3	23.8	258	17	13:23
September	29.4	21.1	205	17	12:24
October	24.4	14.8	112	11	11:24
November	18.5	8.3	89	9	10:29
December	12.4	2.9	70	9	10:00

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

All the nearest cities on our list plant watermelon later than Kumamoto; the closest date is in Fukuoka, 3 days later.

City	Distance	Date	Difference
Fukuoka	92 km	5 May – 11 September	3 days later
Kitakyushu	121 km	from 15 May	13 days later
Kagoshima	134 km	6 May – 16 September	4 days later
Hiroshima	239 km	26 May – 16 August	24 days later
Busan	305 km	15 May – 13 August	13 days later
Ulsan	331 km	18 May – 7 August	16 days later

Where to buy watermelon plants and seeds near Kumamoto

Buy plants ready to set out from 2 May to 24 August (from 11 April to 24 August for an unheated greenhouse); seed for raising your own is sown from 14 March to 27 July. Within 15 km of Kumamoto OpenStreetMap lists 3 garden centres, 5 markets and 2 farm shops (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.

Questions