Cold hardiness & minimum temperature

Is Crystal Palace lobelia (Lobelia erinus 'Crystal Palace')cold hardy? Hardiness zone & min temp

Also called Crystal Palace lobelia, edging lobelia, trailing lobelia, annual lobelia.

More about crystal palace lobelia

About Crystal Palace lobelia

Lobelia erinus 'Crystal Palace' · also called Crystal Palace lobelia, edging lobelia · flowering

Crystal Palace lobelia is a compact, mounding cultivar of Lobelia erinus bearing a dense carpet of deep navy-blue flowers with a white eye above dark bronze-green foliage. A cool-season annual, it thrives in bright conditions with consistent moisture and is ideal for edging, containers and hanging baskets. Contains lobeline alkaloids — treat as toxic to pets.

Cold limit: USDA 10-11 (grown as a cool-season annual in zones 2-9) · RHS H2 (10-21°C)

Watch for — Heat collapse and die-back: Lobelia erinus is a cool-season plant and goes dormant or dies back in sustained temperatures above 27°C — shear plants back by half, keep moist and they often recover when temperatures drop.

What crystal palace lobelia's hardiness rating actually means

Hardiness works differently for crystal palace 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 10-11 (grown as a cool-season annual in zones 2-9) — 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 crystal palace 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 crystal palace 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 crystal palace 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 crystal palace lobelia

Crystal Palace 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.

Crystal Palace lobelia hardiness — frequently asked questions

Is crystal palace lobelia cold hardy?

Hardiness works differently for crystal palace 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. Crystal Palace lobelia is grown 10-11 (grown as a cool-season annual in zones 2-9); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature crystal palace 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 crystal palace lobelia?

Crystal Palace lobelia is rated USDA 10-11 (grown as a cool-season annual in zones 2-9) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can crystal palace 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 crystal palace 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.