When to plant tomatoes in Helena: 6 June – 13 June

In Helena, tomato: sow for seedlings from 25 March to 22 April; plant into a greenhouse from 16 May to 13 June; plant out into open ground from 6 June to 13 June. For plants and seeds, the places nearby include Keeping It Green (plant nursery, 1 km); addresses and opening hours are below.

Tomato in Helena: soil, season and weather

In Helena the soil, not frost, sets the date: the last frost is over around 19 May, but the top 7 cm of soil reaches 15 °C — the minimum on the tomato card — only around 6 June, 18 days later. 119 days separate planting out (6 June) from the first autumn frost (3 October); the card's 70 days to the first harvest leave 49 for picking, so a start 7 weeks late would still fit.

Last spring frost	19 May
Top 7 cm of soil at 15 °C	6 June, 18 days after the last frost
Into an unheated greenhouse	16 May – 13 June; May outside: 3.2 °C at night, 16.2 °C by day; card 16–27 °C
First autumn frost	3 October, 119 days after the start
Days in the bed to the first harvest (card)	70
First harvest, if planted in this window	15 August – 22 August
Days left for picking	49
Daylight	13:33 on 15 April, 15:41 on 6 June
Watering outdoors when fruiting (card)	every 3 days; the driest month, July, has 6 rainy days

Tomato in Helena: care after planting

Planted on 6 June: in the first weeks water every 4 days.

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

6 June — feed: balanced (NPK)
4 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 Helena during the tomato season

Days average above the tomato card's 16–27 °C in July (27.3 °C). Months that stay below 16 °C even by day on average: October (12 °C). Nights average below 16 °C in every month of the season, from 0.6 °C to 12.1 °C.

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
June	21.8	7.9	69	11	15:49
July	27.3	12.1	23	6	15:29
August	26.5	11.5	28	5	14:14
September	21.1	7.4	40	7	12:36
October	12	0.6	46	9	10:58

ERA5 2016–2025, Open-Meteo

Tomato in nearby cities

All the nearest cities on our list plant tomato earlier than Helena; the closest date is in Missoula, 3 days earlier.

City	Distance	Date	Difference
Missoula	155 km	3 June – 16 June	3 days earlier
Billings	287 km	11 May – 24 June	26 days earlier
Idaho Falls	345 km	18 May – 24 June	19 days earlier
Spokane	425 km	15 May – 25 June	22 days earlier
Boise	466 km	27 April – 7 July	40 days earlier
Calgary	517 km	3 June – 11 June	3 days earlier

Where to buy tomato plants and seeds near Helena

Buy plants ready to set out from 6 June to 13 June (from 16 May to 13 June for an unheated greenhouse); seed for raising your own is sown from 25 March to 22 April. Within 15 km of Helena OpenStreetMap lists 2 farm-supply shops and 6 plant nurseries (collected 28 October 2026).

Keeping It Green — plant nursery
Columbia Avenue 2005, 59601 Helena · 1 km · keeping-it-green-helena.com
Gardenwerks: Nursery & Landscaping — plant nursery
2 km
Chadwick Nursery — plant nursery
4 km
Valley Farms — plant nursery
5 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