When to plant watermelons in Portland, Maine: 20 June – 26 July

In Portland, Maine, watermelon: sow for seedlings from 2 May to 28 June; plant into a greenhouse from 30 May to 26 July; plant out into open ground from 20 June to 26 July. For plants and seeds, the places nearby include Allen Sterling & Lothrop (garden centre, 7 km) and Skillins Greenhouses (Trees) (garden centre, 7 km); addresses and opening hours are below.

Watermelon in Portland, Maine: soil, season and weather

In Portland, Maine the soil, not frost, sets the date: the last frost is over around 15 April, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 20 June, 66 days later.

Last spring frost	15 April
Top 7 cm of soil at 18 °C	20 June, 66 days after the last frost
Into an unheated greenhouse	30 May – 26 July; May outside: 8.2 °C at night, 17.3 °C by day; card 18–35 °C
First autumn frost	4 November, 137 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	18 August – 23 September
Days left for picking	78
Daylight	14:58 on 23 May, 15:27 on 20 June
Watering outdoors when fruiting (card)	every 5 days; the driest month, September, has 9 rainy days

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

Watermelon in Portland, Maine: care after planting

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

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

20 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 Portland, Maine during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, July, averages 26.1 °C. Months that stay below 18 °C even by day on average: October (15.6 °C) and November (8.4 °C). Nights average below 18 °C in every month of the season, from 1.2 °C to 17.9 °C.

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
June	22.6	13.9	85	11	15:25
July	26.1	17.9	95	11	15:08
August	25.3	17.2	83	10	14:01
September	21.7	13.7	80	9	12:33
October	15.6	8.1	121	10	11:05
November	8.4	1.2	95	9	9:42

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Portland, Maine, Boston is 22 days earlier and Bangor 5 days later.

City	Distance	Date	Difference
Augusta	82 km	22 June – 25 July	2 days later
Concord	115 km	1 June – 22 July	19 days earlier
Manchester (United States)	122 km	30 May – 24 July	21 days earlier
Boston	159 km	29 May – 4 August	22 days earlier
Bangor	179 km	25 June – 25 July	5 days later
Montpelier	196 km	20 June – 8 July	same day

Where to buy watermelon plants and seeds near Portland, Maine

Buy plants ready to set out from 20 June to 26 July (from 30 May to 26 July for an unheated greenhouse); seed for raising your own is sown from 2 May to 28 June. Within 15 km of Portland, Maine OpenStreetMap lists 5 garden centres, 6 markets and 1 farm shop (collected 20 October 2026).

Allen Sterling & Lothrop — garden centre
Route 1 191, 04105 Falmouth · 7 km
O'Days Nursery — garden centre
County Road 132, 04074 Scarborough · 12 km
Skillins Greenhouses (Trees) — garden centre
Mon–Fri 08:00–18:00; Sat 08:00–17:00; Sun 09:00–17:00 · 7 km
Skillens Greenhouses — garden centre
Mon–Fri 08:00–18:00; Sat 08:00–17:00; Sun 09:00–17:00 · 7 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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