When to plant bulb fennel in Washington, District of Columbia
March 24 – April 7
Direct-sow outdoors · typical Washington yearClimate basis: NOAA station Washington Reagan AP, VA (USW00013743), 3 mi (5 km) from downtown Washington (ZCTA 20004 centroid), elevation 10 ft, on the 1991–2020 climate normals. Direct-sow bulb fennel from approximately the dates above, anchored to the median last spring 32°F freeze (March 24). One year in ten still freezes after April 6.
The Washington year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to Apr 6
Every method, with its sources
Start seeds indoors
Feb 10 – Feb 24Wisconsin Horticulture (University of Wisconsin-Madison Division of Extension) states "Plants can be started indoors 4 to 6 weeks before the last spring frost," giving a sowing span from six to four weeks ahead of the last frost; no competing extension figure was found, so it is encoded as printed. Anchored to the median last spring freeze (Mar 24). University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture)
Direct-sow outdoors
Mar 24 – Apr 7The same Wisconsin Horticulture article says to "Sow seeds about ¼ inch deep after the last frost in spring, or in mid-summer for a fall crop of Florence fennel," and the first clause is a point rule at the last frost that opens a 14-day sowing span; the article's mid-summer alternative is a fixed-calendar rule with no frost relation and so was not encoded. Anchored to the median last spring freeze (Mar 24). University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture)
Variety assumption: Assumes a bulbing Florence type (finocchio) rather than the non-bulbing herb fennel grown for leaf and seed; the cited article covers Foeniculum vulgare generally but names Florence fennel explicitly in its sowing sentence.
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 (1)
- University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture): Fennel, Foeniculum vulgare, Susan Mahr (accessed 2026-07-25)"Plants can be started indoors 4 to 6 weeks before the last spring frost."