Cold hardiness & minimum temperature

Is Lobelia erinus 'Riviera Lilac' (Lobelia erinus 'Riviera Lilac')cold hardy? Hardiness zone & min temp

Also called Riviera Lilac Lobelia, Compact Lilac Lobelia.

More about lobelia erinus 'riviera lilac'

About Lobelia erinus 'Riviera Lilac'

Lobelia erinus 'Riviera Lilac' · also called Riviera Lilac Lobelia, Compact Lilac Lobelia · flowering

'Riviera Lilac' is a compact, bushy edging lobelia carrying masses of soft lilac flowers from early summer. Part of an early-flowering uniform series, it forms tidy mounds ideal for bedding, edging and the front of containers. Like all lobelias it prefers cool, moist, fertile conditions and may slow in peak summer heat.

Cold limit: USDA 10-11 (grown as a half-hardy annual elsewhere) · RHS H2 (10-24°C)

Watch for — Heat-induced stall: High summer temperatures pause flowering and can brown the mound; shear lightly, water and feed to coax a fresh flush when it cools.

What lobelia erinus 'riviera lilac''s hardiness rating actually means

Lobelia erinus 'Riviera Lilac' is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. 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 half-hardy annual elsewhere) — 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

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Lobelia erinus 'Riviera Lilac' shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for lobelia erinus 'riviera lilac' as it gets too cold:

Down to roughly about 1 to 5 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can lobelia erinus 'riviera lilac' go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 10-11 (grown as a half-hardy annual elsewhere) or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

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 lobelia erinus 'riviera lilac' 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 lobelia erinus 'riviera lilac'

Lobelia erinus 'Riviera Lilac' is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Lobelia erinus 'Riviera Lilac' hardiness — frequently asked questions

Is lobelia erinus 'riviera lilac' cold hardy?

Lobelia erinus 'Riviera Lilac' is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 10-11 (grown as a half-hardy annual elsewhere) (and sheltered UK gardens) lobelia erinus 'riviera lilac' can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature lobelia erinus 'riviera lilac' can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Lobelia erinus 'Riviera Lilac' shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is lobelia erinus 'riviera lilac'?

Lobelia erinus 'Riviera Lilac' is rated USDA 10-11 (grown as a half-hardy annual elsewhere) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can lobelia erinus 'riviera lilac' survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 10-11 (grown as a half-hardy annual elsewhere) or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect lobelia erinus 'riviera lilac' from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.