When to plant watermelons in Tokyo: 28 April – 4 September

In Tokyo, watermelon: sow for seedlings from 10 March to 7 August; plant into a greenhouse from 7 April to 4 September; plant out into open ground from 28 April to 4 September.

Watermelon in Tokyo: soil, season and weather

In Tokyo the soil, not frost, sets the date: the last frost is over around 17 March, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 28 April, 42 days later.

Last spring frost	17 March
Top 7 cm of soil at 18 °C	28 April, 42 days after the last frost
Into an unheated greenhouse	7 April – 4 September; April outside: 10.1 °C at night, 19.2 °C by day; card 18–35 °C
First autumn frost	14 December, 230 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	26 June – 2 November
Days left for picking	171
Daylight	12:32 on 31 March, 13:31 on 28 April
Watering outdoors when fruiting (card)	every 5 days; the driest month, December, has 6 rainy days

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

Watermelon in Tokyo: care after planting

Planted on 28 April: in the first weeks water every 5 days.

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

28 April — 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 Tokyo 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 °C. Months that stay below 18 °C even by day on average: November (16.8 °C) and December (11.6 °C). Nights average below 18 °C in April, May and October–December (2.2–14.8 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
April	19.2	10.1	127	12	13:05
May	23.5	14.8	151	13	14:02
June	26.7	19.2	188	16	14:34
July	30.6	23.4	170	16	14:21
August	32	24.5	139	14	13:32
September	28.1	21.1	194	15	12:26
October	21.9	14.3	195	13	11:20
November	16.8	8.1	86	9	10:18
December	11.6	2.2	51	6	9:46

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

All the nearest cities on our list plant watermelon later than Tokyo; the closest date is in Hamamatsu, 4 days later.

City	Distance	Date	Difference
Hamamatsu	209 km	2 May – 8 September	4 days later
Niigata	255 km	20 May – 10 September	22 days later
Nagoya	259 km	6 May – 31 August	8 days later
Sendai	305 km	7 June – 14 August	40 days later
Kyoto	363 km	14 May – 28 August	16 days later
Osaka	397 km	5 May – 7 September	7 days later

Where to buy watermelon plants and seeds near Tokyo

Buy plants ready to set out from 28 April to 4 September (from 7 April to 4 September for an unheated greenhouse); seed for raising your own is sown from 10 March to 7 August. Within 15 km of Tokyo OpenStreetMap lists 30 garden centres, 3 farm-supply shops, 1 plant nursery, 28 markets and 31 farm shops (collected 28 October 2026).

Ameya-Yokocho — market
8 km · ameyoko.net
べじふるセンター練馬 — market
9 km
Setagaya Wholesale Market — market
9 km
Uogashi Yokocho (Goods Market) — market
10 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