When to plant watermelons in Osaka: 5 May – 7 September

In Osaka, watermelon: sow for seedlings from 17 March to 10 August; plant into a greenhouse from 14 April to 7 September; plant out into open ground from 5 May to 7 September.

Watermelon in Osaka: soil, season and weather

In Osaka the soil, not frost, sets the date: the last frost is over around 14 March, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 5 May, 52 days later.

Last spring frost	14 March
Top 7 cm of soil at 18 °C	5 May, 52 days after the last frost
Into an unheated greenhouse	14 April – 7 September; April outside: 9.8 °C at night, 18.7 °C by day; card 18–35 °C
First autumn frost	17 December, 226 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	3 July – 5 November
Days left for picking	167
Daylight	12:46 on 7 April, 13:41 on 5 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, December, has 6 rainy days

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

Watermelon in Osaka: care after planting

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

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

5 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 Osaka during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, August, averages 32.5 °C. Months that stay below 18 °C even by day on average: November (16.8 °C) and December (11.1 °C). Nights average below 18 °C in May and October–December (2.8–14.7 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	23	14.5	189	10	13:58
June	26.5	19.1	244	14	14:28
July	30.8	23.9	240	15	14:16
August	32.5	25.1	173	14	13:29
September	28.9	21.7	209	14	12:26
October	22.5	14.7	188	11	11:21
November	16.8	8.3	72	7	10:22
December	11.1	2.8	49	6	9:51

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Osaka, Tokyo is 7 days earlier and Hiroshima 21 days later.

City	Distance	Date	Difference
Kyoto	43 km	14 May – 28 August	9 days later
Nagoya	139 km	6 May – 31 August	1 day later
Okayama	145 km	14 May – 5 September	9 days later
Hamamatsu	204 km	2 May – 8 September	3 days earlier
Hiroshima	281 km	26 May – 16 August	21 days later
Tokyo	397 km	28 April – 4 September	7 days earlier

Where to buy watermelon plants and seeds near Osaka

Buy plants ready to set out from 5 May to 7 September (from 14 April to 7 September for an unheated greenhouse); seed for raising your own is sown from 17 March to 10 August. Within 15 km of Osaka OpenStreetMap lists 16 garden centres, 4 farm-supply shops, 3 plant nurseries, 19 markets and 8 farm shops (collected 28 October 2026).

JAグリーン大阪農業協同組合 — farm supply
12 km
Kizu Wholesale Market — market
4 km · kizu-ichiba.com
Amagasaki Public Wgolesale Market — market
9 km · ama-shijoh.net
natural marche ハレバレ — market
7 km · harebareshop.com

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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