When to plant watermelons in Letterkenny: 7 July – 19 August

In Letterkenny, watermelon: sow for seedlings from 19 May to 22 July; plant into a greenhouse from 16 June to 19 August; plant out into open ground from 7 July to 19 August. For plants and seeds, the places nearby include Gary's Petworld and Garden Centre (garden centre, 2 km); addresses and opening hours are below.

Watermelon in Letterkenny: soil, season and weather

In Letterkenny the soil, not frost, sets the date: the last frost is over around 30 March, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 7 July, 99 days later.

Last spring frost	30 March
Top 7 cm of soil at 18 °C	7 July, 99 days after the last frost
Into an unheated greenhouse	16 June – 19 August; June outside: 10.1 °C at night, 16.8 °C by day; card 18–35 °C
First autumn frost	28 November, 144 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	4 September – 17 October
Days left for picking	85
Daylight	17:13 on 9 June, 17:08 on 7 July
Watering outdoors when fruiting (card)	every 5 days; the driest month, September, has 18 rainy days

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

Watermelon in Letterkenny: care after planting

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

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

7 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 Letterkenny during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, August, averages 17.7 °C. Months that stay below 18 °C even by day on average: July–November (9.5–17.7 °C). Nights average below 18 °C in every month of the season, from 4.9 °C to 11.5 °C.

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
July	17.6	11.4	115	18	16:50
August	17.7	11.5	126	20	15:01
September	15.8	9.8	102	18	12:48
October	12.8	7.9	120	18	10:35
November	9.5	4.9	103	18	8:27

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Letterkenny, Sligo is 7 days earlier and Dundalk 10 days later.

City	Distance	Date	Difference
Derry	26 km	13 July – 12 August	6 days later
Sligo	91 km	30 June – 12 August	7 days earlier
Belfast	122 km	7 July – 10 August	same day
Dundalk	137 km	17 July – 11 August	10 days later
Athlone	172 km	13 July – 17 August	6 days later
Dublin	203 km	16 July – 15 August	9 days later

Where to buy watermelon plants and seeds near Letterkenny

Buy plants ready to set out from 7 July to 19 August (from 16 June to 19 August for an unheated greenhouse); seed for raising your own is sown from 19 May to 22 July. Within 15 km of Letterkenny OpenStreetMap lists 3 garden centres and 1 market (collected 28 October 2026).

Gary's Petworld and Garden Centre — garden centre
Mon–Fri 09:00–18:00 · 2 km
Alcorns — garden centre
2 km · alcorns.ie
Raphoe Garden Centre — garden centre
12 km
Market Square — market
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.

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