When to plant watermelons in Hamamatsu: 2 May – 8 September

In Hamamatsu, watermelon: sow for seedlings from 14 March to 11 August; plant into a greenhouse from 11 April to 8 September; plant out into open ground from 2 May to 8 September.

Watermelon in Hamamatsu: soil, season and weather

In Hamamatsu the soil, not frost, sets the date: the last frost is over around 24 February, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 2 May, 67 days later.

Last spring frost	24 February
Top 7 cm of soil at 18 °C	2 May, 67 days after the last frost
Into an unheated greenhouse	11 April – 8 September; April outside: 10.4 °C at night, 19.4 °C by day; card 18–35 °C
First autumn frost	18 December, 230 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	30 June – 6 November
Days left for picking	171
Daylight	12:39 on 4 April, 13:36 on 2 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, December, has 6 rainy days

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

Watermelon in Hamamatsu: 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 Hamamatsu during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, August, averages 31.3 °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 (4–15.4 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	23.2	14.6	244	12	13:58
June	26.1	18.8	357	15	14:28
July	29.9	23.3	310	16	14:16
August	31.3	24.4	218	17	13:29
September	28.2	21.3	277	18	12:26
October	23	15.4	227	14	11:21
November	18	9.4	117	9	10:22
December	12.4	4	71	6	9:51

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Hamamatsu, Tokyo is 4 days earlier and Niigata 18 days later.

City	Distance	Date	Difference
Nagoya	92 km	6 May – 31 August	4 days later
Kyoto	182 km	14 May – 28 August	12 days later
Osaka	204 km	5 May – 7 September	3 days later
Tokyo	209 km	28 April – 4 September	4 days earlier
Okayama	348 km	14 May – 5 September	12 days later
Niigata	376 km	20 May – 10 September	18 days later

Where to buy watermelon plants and seeds near Hamamatsu

Buy plants ready to set out from 2 May to 8 September (from 11 April to 8 September for an unheated greenhouse); seed for raising your own is sown from 14 March to 11 August. Within 15 km of Hamamatsu OpenStreetMap lists 5 garden centres, 6 farm-supply shops, 5 markets and 39 farm shops (collected 28 October 2026).

倉田園 — farm shop · sells: strawberry
10 km · kurataen.com
アグリス浜名湖 — farm shop
10 km · agurisu-hamanako.com
やっほ～ — farm shop
4 km
うなぎいも — farm shop · sells: sweet_potato
4 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