Cold hardiness & minimum temperature

Is Edging lobelia (Lobelia erinus)cold hardy? Hardiness zone & min temp

Also called edging lobelia, trailing lobelia, bedding lobelia.

More about edging lobelia

About Edging lobelia

Lobelia erinus · also called edging lobelia, trailing lobelia · flowering

A compact, profusely flowering half-hardy annual producing masses of small, vivid blue, violet, white, or red flowers from late spring until autumn frost. Ideal for edging, hanging baskets, and containers. Prefers cool, moist conditions and partial shade in hot climates. Regular watering and cool temperatures sustain its long flowering season.

Cold limit: USDA Annual in zones 2–10; short-lived perennial in zone 10–11 · RHS H2 (10–22 °C optimal; frost-tender below 0 °C)

Watch for — Flowering halt in summer heat: Above 27 °C (80 °F), lobelia commonly stops blooming and may look exhausted. Move containers to a shadier spot, water consistently, and shear plants back lightly. Flowering resumes when cooler temperatures return in late summer or autumn.

What edging lobelia's hardiness rating actually means

Hardiness works differently for edging lobelia: it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". Its RHS rating of H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA Annual in zones 2–10; short-lived perennial in zone 10–11 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

Concretely, for edging lobelia as it gets too cold:

Light frost (around 0 to −2 °C) damages or kills tender summer crops outright; cold-hardy types take a few degrees of frost.
The plant does not "survive winter" — its life cycle simply ends, by design, when frost arrives or it finishes cropping.
A surprise late spring frost can also kill young transplants set out too early, before the season even starts.

Can edging lobelia go outside or overwinter — and where?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost.
In short-season zones, start it indoors or under cover to stretch the effective growing window.
Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when edging lobelia can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline edging lobelia

Edging lobelia is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks.
Have row cover ready for an unexpected late spring or early autumn frost.
Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.

Edging lobelia hardiness — frequently asked questions

Is edging lobelia cold hardy?

Hardiness works differently for edging lobelia: it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". A seasonal crop, not a perennial. Edging lobelia is grown as an annual in USDA Annual in zones 2–10; short-lived perennial in zone 10–11; you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature edging lobelia can survive?

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

What hardiness zone is edging lobelia?

Edging lobelia is rated USDA Annual in zones 2–10; short-lived perennial in zone 10–11 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can edging lobelia survive winter outside?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost. In short-season zones, start it indoors or under cover to stretch the effective growing window. Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

How do I protect edging lobelia from frost?

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks. Have row cover ready for an unexpected late spring or early autumn frost. Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.