When to plant bulb fennel in Knoxville, Tennessee

April 11 – April 25

Direct-sow outdoors · typical Knoxville year

Climate basis: NOAA station Knoxville Exp Stn, TN (USC00404946), 5 mi (8 km) from downtown Knoxville (ZCTA 37902 centroid), elevation 830 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 (April 11). One year in ten still freezes after April 29.

Last spring freezeApril 111-in-10 after Apr 29

First fall freezeOctober 281-in-10 before Oct 13

Frost-free season≈ 198 daysmedian at 32°F

Hard freeze, 28°Mar 31 – Nov 6kills even hardy greens

USDA zone7b5 to 10°F winter low — not frost timing

The Knoxville year

Start seeds indoorsFeb 28 – Mar 14

Direct-sow outdoorsApr 11 – Apr 25

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 29

Bulb Fennel in Knoxville · freeze context from Knoxville Exp Stn, TN, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Feb 28 – Mar 14

Wisconsin 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 (Apr 11). University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture)

Direct-sow outdoors

Apr 11 – Apr 25

The 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 (Apr 11). 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.

This week, not a typical year:

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."

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