When to plant watermelons in Niigata: 20 May – 10 September

In Niigata, watermelon: sow for seedlings from 1 April to 13 August; plant into a greenhouse from 29 April to 10 September; plant out into open ground from 20 May to 10 September.

Watermelon in Niigata: soil, season and weather

In Niigata the soil, not frost, sets the date: the last frost is over around 8 March, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 20 May, 73 days later.

Last spring frost	8 March
Top 7 cm of soil at 18 °C	20 May, 73 days after the last frost
Into an unheated greenhouse	29 April – 10 September; April outside: 7.8 °C at night, 15.2 °C by day; card 18–35 °C
First autumn frost	20 December, 214 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	18 July – 8 November
Days left for picking	155
Daylight	13:26 on 22 April, 14:21 on 20 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, May, has 13 rainy days

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

Watermelon in Niigata: care after planting

Planted on 20 May: in the first weeks water every 5 days.

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

20 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 Niigata during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, August, averages 29.9 °C. Months that stay below 18 °C even by day on average: November (14.3 °C) and December (8.4 °C). Nights average below 18 °C in May, June and October–December (3.8–17.9 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	20.7	13	119	13	14:12
June	24.1	17.9	137	12	14:47
July	28.3	22.9	219	14	14:33
August	29.9	24.2	211	14	13:39
September	26.3	20.7	190	15	12:28
October	19.9	14.3	163	15	11:16
November	14.3	8.7	168	19	10:09
December	8.4	3.8	259	26	9:33

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Niigata, Tokyo is 22 days earlier and Sendai 18 days later.

City	Distance	Date	Difference
Sendai	165 km	7 June – 14 August	18 days later
Tokyo	255 km	28 April – 4 September	22 days earlier
Nagoya	360 km	6 May – 31 August	14 days earlier
Hamamatsu	376 km	2 May – 8 September	18 days earlier
Kyoto	436 km	14 May – 28 August	6 days earlier
Osaka	479 km	5 May – 7 September	15 days earlier

Where to buy watermelon plants and seeds near Niigata

Buy plants ready to set out from 20 May to 10 September (from 29 April to 10 September for an unheated greenhouse); seed for raising your own is sown from 1 April to 13 August. Within 15 km of Niigata OpenStreetMap lists 4 garden centres, 4 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.

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