When to plant lemon balm in Portland, Maine

April 26 – May 10

Transplant outdoors · typical Portland year

Climate basis: NOAA station Portland INTL Jetport, ME (USW00014764), 2 mi (4 km) from downtown Portland (ZCTA 04101 centroid), elevation 45 ft, on the 1991–2020 climate normals. Transplant lemon balm outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (April 26). One year in ten still freezes after May 7.

Last spring freezeApril 261-in-10 after May 7

First fall freezeOctober 151-in-10 before Oct 2

Frost-free season≈ 170 daysmedian at 32°F

Hard freeze, 28°Apr 14 – Oct 27kills even hardy greens

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

The Portland year

Start seeds indoorsMar 15 – Mar 29

Transplant outdoorsApr 26 – May 10

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 7

Lemon Balm in Portland · freeze context from Portland INTL Jetport, ME, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 15 – Mar 29

Wisconsin Horticulture sows lemon balm indoors about 4 to 6 weeks before the last spring frost, so the window runs 6 to 4 weeks before that date. Anchored to the median last spring freeze (Apr 26). University of Wisconsin-Madison Division of Extension, Wisconsin Horticulture · Virginia Cooperative Extension, Virginia Tech

Transplant outdoors

Apr 26 – May 10

Wisconsin Horticulture ties lemon balm transplanting to seedling height rather than a date, so the frost anchor comes from Virginia Cooperative Extension's herb publication — whose herb table lists lemon balm — which sets all herb plants out after the danger of severe frost has passed. Anchored to the median last spring freeze (Apr 26). Virginia Cooperative Extension, Virginia Tech

Variety assumption: A hardy perennial that self-seeds freely; these windows apply to first-year plantings from seed or nursery plants.

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)

University of Wisconsin-Madison Division of Extension, Wisconsin Horticulture: Lemon Balm, Melissa officinalis (accessed 2026-07-25)
"Lemon balm can be started from seed sown indoors about 4 to 6 weeks before the last spring frost, although seeds may be somewhat slow to germinate."
Virginia Cooperative Extension, Virginia Tech: Herb Culture and Use (Publication 426-420) (accessed 2026-07-25)
"In addition, many culinary herbs, such as tarragon, can only be propagated asexually; seed-grown plants lack the oils that give them flavor."

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