When to plant watermelons in Hiroshima: 26 May – 16 August

In Hiroshima, watermelon: sow for seedlings from 7 April to 19 July; plant into a greenhouse from 5 May to 16 August; plant out into open ground from 26 May to 16 August.

Watermelon in Hiroshima: soil, season and weather

In Hiroshima the soil, not frost, sets the date: the last frost is over around 9 April, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 26 May, 47 days later.

Last spring frost	9 April
Top 7 cm of soil at 18 °C	26 May, 47 days after the last frost
Into an unheated greenhouse	5 May – 16 August; May outside: 11 °C at night, 20.7 °C by day; card 18–35 °C
First autumn frost	25 November, 183 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	24 July – 14 October
Days left for picking	124
Daylight	13:27 on 28 April, 14:11 on 26 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, November, has 6 rainy days

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

Watermelon in Hiroshima: care after planting

Planted on 26 May: in the first weeks water every 5 days.

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

26 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 Hiroshima 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 (4.9–15.7 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	20.7	11	146	10	13:57
June	24	15.7	239	15	14:26
July	27.8	20.7	290	16	14:15
August	29.7	21.6	216	15	13:28
September	26	18	219	15	12:25
October	20.4	11.2	110	9	11:22
November	14.7	4.9	62	6	10:23

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

All the nearest cities on our list plant watermelon earlier than Hiroshima; the closest date is in Kitakyushu, 11 days earlier.

City	Distance	Date	Difference
Okayama	138 km	14 May – 5 September	12 days earlier
Kitakyushu	155 km	from 15 May	11 days earlier
Fukuoka	209 km	5 May – 11 September	21 days earlier
Kumamoto	239 km	2 May – 24 August	24 days earlier
Osaka	281 km	5 May – 7 September	21 days earlier
Kyoto	311 km	14 May – 28 August	12 days earlier

Where to buy watermelon plants and seeds near Hiroshima

Buy plants ready to set out from 26 May to 16 August (from 5 May to 16 August for an unheated greenhouse); seed for raising your own is sown from 7 April to 19 July. Within 15 km of Hiroshima OpenStreetMap lists 2 garden centres, 2 farm-supply shops, 3 markets and 2 farm shops (collected 28 October 2026).

アルパーク — market
5 km
佐伯商店 — farm shop
3 km
無人市 — farm shop
3 km
グリーンセンター深川店 — garden centre
13 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