When to plant tomatoes in Sion: 21 June – 29 June

In Sion, tomato: sow for seedlings from 9 April to 8 May; plant into a greenhouse from 31 May to 29 June; plant out into open ground from 21 June to 29 June. For plants and seeds, the places nearby include Point Vert (garden centre, 5 km) and Multiplants (garden centre, 6 km); addresses and opening hours are below.

Tomato in Sion: soil, season and weather

In Sion the soil, not frost, sets the date: the last frost is over around 8 May, but the top 7 cm of soil reaches 15 °C — the minimum on the tomato card — only around 21 June, 44 days later. 120 days separate planting out (21 June) from the first autumn frost (19 October); the card's 70 days to the first harvest leave 50 for picking, so a start 7 weeks late would still fit.

Last spring frost	8 May
Top 7 cm of soil at 15 °C	21 June, 44 days after the last frost
Into an unheated greenhouse	31 May – 29 June; May outside: 4.1 °C at night, 14.5 °C by day; card 16–27 °C
First autumn frost	19 October, 120 days after the start
Days in the bed to the first harvest (card)	70
First harvest, if planted in this window	30 August – 7 September
Days left for picking	50
Daylight	14:17 on 30 April, 15:47 on 21 June
Watering outdoors when fruiting (card)	every 3 days; the driest month, September, has 12 rainy days

Tomato in Sion: care after planting

Planted on 21 June: in the first weeks water every 4 days.

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

21 June — feed: balanced (NPK)
19 July — feed: nitrogen

Pests and diseases of tomato 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 Sion during the tomato season

No month of the season averages above the tomato card's 16–27 °C by day; the warmest, August, averages 22 °C. Months that stay below 16 °C even by day on average: October (13.7 °C). Nights average below 16 °C in every month of the season, from 2.9 °C to 11.1 °C.

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
June	20.2	9.5	125	18	15:46
July	21.8	11.1	115	16	15:27
August	22	10.8	103	14	14:12
September	17.7	7.1	91	12	12:36
October	13.7	2.9	105	12	10:59

ERA5 2016–2025, Open-Meteo

Tomato in nearby cities

Around Sion, Neuchâtel is 38 days earlier and Aosta 13 days later.

City	Distance	Date	Difference
Aosta	55 km	from 4 July	13 days later
Lausanne	65 km	2 June – 31 July	19 days earlier
Fribourg	65 km	5 June – 17 July	16 days earlier
Bern	80 km	3 June – 14 July	18 days earlier
Neuchâtel	91 km	14 May – 8 August	38 days earlier
Geneva	94 km	28 May – 28 July	24 days earlier

Where to buy tomato plants and seeds near Sion

Buy plants ready to set out from 21 June to 29 June (from 31 May to 29 June for an unheated greenhouse); seed for raising your own is sown from 9 April to 8 May. Within 15 km of Sion OpenStreetMap lists 4 garden centres, 1 farm-supply shop, 1 plant nursery, 1 market and 4 farm shops (collected 27 October 2026).

Agrol — garden centre
Route de Sion 90, 3960 Sierre · Mon–Thu 08:00–18:30; Fri 08:00–20:00; Sat 08:00–17:00 · 13 km · agrol.ch
Multiplants — garden centre
Route des Charmilles 42, 1963 Vétroz · 6 km · multiplants.ch
Point Vert — garden centre
Mon–Thu 08:00–18:30; Sat 08:00–17:00; Fri 08:00–20:00 · 5 km
Marché de la vieille ville — market
Fri 08:00–14:00 · 0 km · mvvsion.ch

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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