When to plant snapdragon in Boise, Idaho

April 19 – May 3

Transplant outdoors · typical Boise year

Climate basis: NOAA station Boise 7 N, ID (USC00101017), 6 mi (9 km) from downtown Boise (ZCTA 83702 centroid), elevation 3885 ft, on the 1991–2020 climate normals. Transplant snapdragon outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 17). One year in ten still freezes after June 10.

Last spring freezeMay 171-in-10 after Jun 10

First fall freezeOctober 121-in-10 before Sep 27

Frost-free season≈ 147 daysmedian at 32°F

Hard freeze, 28°Apr 27 – Oct 24kills even hardy greens

USDA zone7a0 to 5°F winter low — not frost timing

The Boise year

Start seeds indoorsMar 22 – Apr 5

Transplant outdoorsApr 19 – May 3

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Jun 10

Snapdragon in Boise · freeze context from Boise 7 N, ID, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 22 – Apr 5

Colorado State's seed-starting table lists snapdragon at 8 weeks before the average frost-free date in the 'Indoors' column, the longest lead time of any source found, so indoor sowing opens 8 weeks before the median last freeze and runs a two-week span. Anchored to the median last spring freeze (May 17). Colorado State University Extension

Transplant outdoors

Apr 19 – May 3

Illinois Extension names snapdragon in its hardy-annual list and states those can usually be planted about four weeks before the frost-free date, so transplanting opens 4 weeks before the median last freeze. Anchored to the median last spring freeze (May 17). University of Illinois Extension

Variety assumption: Assumes ordinary bedding and cut-flower strains of Antirrhinum majus grown as an annual; it is a hardy annual that flowers best in cool weather and Colorado State's 8-week indoor lead time reflects its slow start from very fine seed.

These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.

This week, not a typical year:

Crop rule sources (2)

Colorado State University Extension: Growing Annual Plants from Seed (accessed 2026-07-25)
"Table 1: Starting times for seeds grown indoors and in cold frames, shown as number of weeks to start seed before average frost-free date."
University of Illinois Extension: Annuals — Flowers (accessed 2026-08-26)
The current page names snapdragon as a hardy annual and says hardy annuals can usually be planted about four weeks before the local frost-free date.

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