When to plant radicchio in Seattle, Washington
March 13 – March 27
Transplant outdoors · typical Seattle yearClimate basis: NOAA station Seattle Boeing Fld, WA (USW00024234), 5 mi (8 km) from downtown Seattle (ZCTA 98104 centroid), elevation 20 ft, on the 1991–2020 climate normals. Transplant radicchio outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (March 13). One year in ten still freezes after April 1.
The Seattle year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to Apr 1
Every method, with its sources
Transplant outdoors
Mar 13 – Mar 27USU places transplants near the last frost-free date, a point rule that is encoded as a 14-day planting span beginning at the last-freeze anchor. Anchored to the median last spring freeze (Mar 13). Utah State University Extension
Direct-sow outdoors
Feb 13 – Feb 20USU states seeded radicchio may go in 3-4 weeks before the last frost-free date, and because the source gives an explicit range it is encoded directly as -28 to -21 days rather than expanded to a 14-day span. Anchored to the median last spring freeze (Mar 13). Utah State University Extension
Fall planting
Aug 19 – Sep 2UMN sows the fall crop about three months before the average first fall frost, taken as a -90 day point and encoded as a 14-day span; USU's fall guidance is not combined here because it is anchored to an anticipated maturity date rather than stated directly against the frost date. Anchored to the median first fall freeze (Nov 17). University of Minnesota Extension
Start seeds indoors
Not calculatedNo frost-anchored indoor-start window is published, because UMN gives indoor sowing as Minnesota calendar dates ('early April', and July for fall crops) rather than against a freeze date, and the alternative lead time it offers is measured from the transplant date rather than from an anchor, while USU states only that 5-6 weeks are generally required to grow transplants to set-out size.
Variety assumption: UMN gives radicchio about 60 to 70 days to mature, and USU advises selecting early-maturing cultivars for fall plantings.
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.
Crop rule sources (2)
- Utah State University Extension: How to Grow Chicory in Your Garden (accessed 2026-07-25)"Seeded radicchio may be planted 3-4 weeks before the last frost-free date for the growing area."
- University of Minnesota Extension: Growing lettuce, endive and radicchio in home gardens (accessed 2026-07-25)"For a fall crop, sow seed about three months before the average first fall frost date."