When to plant watermelons in Derry: 13 July – 12 August

In Derry, watermelon: sow for seedlings from 25 May to 15 July; plant into a greenhouse from 22 June to 12 August; plant out into open ground from 13 July to 12 August. For plants and seeds, the places nearby include Culmore Farm Shop (farm shop, 7 km); addresses and opening hours are below.

Watermelon in Derry: soil, season and weather

In Derry the soil, not frost, sets the date: the last frost is over around 23 March, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 13 July, 112 days later.

Last spring frost	23 March
Top 7 cm of soil at 18 °C	13 July, 112 days after the last frost
Into an unheated greenhouse	22 June – 12 August; June outside: 10.4 °C at night, 16.8 °C by day; card 18–35 °C
First autumn frost	21 November, 131 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	10 September – 10 October
Days left for picking	72
Daylight	17:20 on 15 June, 16:56 on 13 July
Watering outdoors when fruiting (card)	every 5 days; the driest month, November, has 17 rainy days

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

Watermelon in Derry: care after planting

Planted on 13 July: in the first weeks water every 5 days.

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

13 July — 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 Derry during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, July, averages 17.7 °C. Months that stay below 18 °C even by day on average: July–November (9.7–17.7 °C). Nights average below 18 °C in every month of the season, from 5.4 °C to 11.9 °C.

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
July	17.7	11.7	104	19	16:51
August	17.7	11.9	113	20	15:02
September	15.9	10.3	101	18	12:48
October	12.9	8.4	106	17	10:35
November	9.7	5.4	90	17	8:26

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Derry, Sligo is 13 days earlier and Dundalk 4 days later.

City	Distance	Date	Difference
Letterkenny	26 km	7 July – 19 August	6 days earlier
Belfast	100 km	7 July – 10 August	6 days earlier
Sligo	110 km	30 June – 12 August	13 days earlier
Dundalk	126 km	17 July – 11 August	4 days later
Athlone	180 km	13 July – 17 August	same day
Dublin	196 km	16 July – 15 August	3 days later

Where to buy watermelon plants and seeds near Derry

Buy plants ready to set out from 13 July to 12 August (from 22 June to 12 August for an unheated greenhouse); seed for raising your own is sown from 25 May to 15 July. Within 15 km of Derry OpenStreetMap lists 1 garden centre and 1 farm shop (collected 28 October 2026).

Culmore Farm Shop — farm shop
Culmore Road, Culmore · 7 km
Altnagelvin Garden Centre — garden centre
2 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