When to plant borage in Denver, Colorado

April 30 – May 14

Direct-sow outdoors · typical Denver year

Climate basis: NOAA station Denver Water Dept, CO (USC00052223), 2 mi (3 km) from downtown Denver (ZCTA 80202 centroid), elevation 5228 ft, on the 1991–2020 climate normals. Direct-sow borage from approximately the dates above, anchored to the median last spring 32°F freeze (April 30). One year in ten still freezes after May 13.

Last spring freezeApril 301-in-10 after May 13

First fall freezeOctober 121-in-10 before Sep 28

Frost-free season≈ 165 daysmedian at 32°F

Hard freeze, 28°Apr 18 – Oct 21kills even hardy greens

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

The Denver 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 13

Borage in Denver · freeze context from Denver Water Dept, CO, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 19 – Apr 2

Illinois Extension permits starting borage indoors but gives no lead time, so the offset comes from Virginia Cooperative Extension's herb publication — whose annual herb table lists borage — which sows small herb seed about six weeks before the last frost date. Anchored to the median last spring freeze (Apr 30). Virginia Cooperative Extension, Virginia Tech

Direct-sow outdoors

Apr 30 – May 14

Illinois Extension sows borage directly in the garden after frost is past, a point rule that opens a two-week sowing span at the last spring freeze. Anchored to the median last spring freeze (Apr 30). University of Illinois Extension · Virginia Cooperative Extension, Virginia Tech

Variety assumption: Virginia Cooperative Extension lists borage as a self-sowing annual; it resents root disturbance, so direct sowing is the usual method.

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 Illinois Extension: Borage | Herbs (accessed 2026-07-25)
"Borage is easily grown from seed started indoors or directly sown in the garden after frost is past."
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."

Keep exploring

This crop, other cities

Related crops in Denver

Local overview