When to plant bulb fennel in Manchester, New Hampshire

April 30 – May 14

Direct-sow outdoors · typical Manchester year

Climate basis: NOAA station Massabesic Lake, NH (USC00275211), 4 mi (6 km) from downtown Manchester (ZCTA 03101 centroid), elevation 253 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 30). One year in ten still freezes after May 14.

Last spring freezeApril 301-in-10 after May 14

First fall freezeOctober 111-in-10 before Sep 30

Frost-free season≈ 164 daysmedian at 32°F

Hard freeze, 28°Apr 17 – Oct 24kills even hardy greens

USDA zone6a-10 to -5°F winter low — not frost timing

The Manchester year

Start seeds indoorsMar 19 – Apr 2

Direct-sow outdoorsApr 30 – May 14

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 14

Bulb Fennel in Manchester · freeze context from Massabesic Lake, NH, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 19 – Apr 2

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 30). University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture)

Direct-sow outdoors

Apr 30 – May 14

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 30). 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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