When to plant watermelons in San Luis: 25 September – 13 March

In San Luis, watermelon: sow for seedlings from 7 August to 14 February; plant into a greenhouse from 4 September to 13 March; plant out into open ground from 25 September to 13 March.

Watermelon in San Luis: soil, season and weather

In San Luis the soil, not frost, sets the date: the last frost is over around 21 August, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 25 September, 35 days later.

Last spring frost	21 August
Top 7 cm of soil at 18 °C	25 September, 35 days after the last frost
Into an unheated greenhouse	4 September – 13 March; September outside: 9.1 °C at night, 21 °C by day; card 18–35 °C
First autumn frost	22 June, 271 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	23 November – 11 May
Days left for picking	212
Daylight	11:16 on 28 August, 12:12 on 25 September
Watering outdoors when fruiting (card)	every 5 days; the driest month, June, has 2 rainy days

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

Watermelon in San Luis: care after planting

Planted on 25 September: in the first weeks water every 5 days.

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

25 September — 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 San Luis during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, January, averages 28.7 °C. Months that stay below 18 °C even by day on average: May (17 °C) and June (14.6 °C). Nights average below 18 °C in March–June and September–December (5.3–17.3 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
September	21	9.1	20	4	11:51
October	23.4	11.7	54	8	12:53
November	26.1	14.9	85	12	13:50
December	28.2	17.3	70	11	14:20
January	28.7	18.6	105	14	14:07
February	27.6	18	78	11	13:17
March	25	15.5	81	11	12:20
April	20.9	12	55	7	11:17
May	17	8.4	30	5	10:25
June	14.6	5.3	13	2	9:58

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around San Luis, San Juan is 7 days earlier and Santiago 19 days later.

City	Distance	Date	Difference
Río Cuarto	184 km	29 September – 4 March	4 days later
San Rafael	238 km	22 September – 24 February	3 days earlier
Mendoza	238 km	19 September – 7 March	6 days earlier
San Juan	284 km	18 September – 10 March	7 days earlier
Córdoba	289 km	1 October – 5 March	6 days later
Santiago	404 km	14 October – 8 March	19 days later

Where to buy watermelon plants and seeds near San Luis

Buy plants ready to set out from 25 September to 13 March (from 4 September to 13 March for an unheated greenhouse); seed for raising your own is sown from 7 August to 14 February. Within 15 km of San Luis OpenStreetMap lists 1 plant nursery (collected 27 October 2026).

Vivero Improfop SAPEM — plant nursery
9 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