When to plant watermelons in Sendai: 7 June – 14 August

In Sendai, watermelon: sow for seedlings from 19 April to 17 July; plant into a greenhouse from 17 May to 14 August; plant out into open ground from 7 June to 14 August. For plants and seeds, the places nearby include Greenhouse Miyama (garden centre, 12 km); addresses and opening hours are below.

Watermelon in Sendai: soil, season and weather

In Sendai the soil, not frost, sets the date: the last frost is over around 31 March, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 7 June, 68 days later.

Last spring frost	31 March
Top 7 cm of soil at 18 °C	7 June, 68 days after the last frost
Into an unheated greenhouse	17 May – 14 August; May outside: 11.1 °C at night, 20.1 °C by day; card 18–35 °C
First autumn frost	23 November, 169 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	5 August – 12 October
Days left for picking	110
Daylight	14:05 on 10 May, 14:44 on 7 June
Watering outdoors when fruiting (card)	every 5 days; the driest month, November, has 9 rainy days

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

Watermelon in Sendai: care after planting

Planted on 7 June: in the first weeks water every 5 days.

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

7 June — 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 Sendai during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, August, averages 27.9 °C. Months that stay below 18 °C even by day on average: November (12.6 °C). Nights average below 18 °C in June and September–November (5–17.5 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
June	23.1	15.6	151	15	14:49
July	26.7	20.1	214	20	14:35
August	27.9	21.2	241	20	13:41
September	24	17.5	201	18	12:28
October	18.1	10.9	163	12	11:15
November	12.6	5	61	9	10:07

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Sendai, Tokyo is 40 days earlier and Sapporo 40 days later.

City	Distance	Date	Difference
Niigata	165 km	20 May – 10 September	18 days earlier
Tokyo	305 km	28 April – 4 September	40 days earlier
Hamamatsu	485 km	2 May – 8 September	36 days earlier
Nagoya	493 km	6 May – 31 August	32 days earlier
Sapporo	534 km	17 July – 19 August	40 days later
Kyoto	582 km	14 May – 28 August	24 days earlier

Where to buy watermelon plants and seeds near Sendai

Buy plants ready to set out from 7 June to 14 August (from 17 May to 14 August for an unheated greenhouse); seed for raising your own is sown from 19 April to 17 July. Within 15 km of Sendai OpenStreetMap lists 2 garden centres, 1 farm-supply shop, 4 markets and 2 farm shops (collected 28 October 2026).

Chuo Wholesale Market — market
6 km
丘の上のマルシェ — market
13 km
大丈夫屋 — farm shop
7 km
Greenhouse Miyama — garden centre
Mon–Sun 09:00–17:30 · 12 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