Cold hardiness & minimum temperature

Is Myrtillocactus geometrizans (Myrtillocactus geometrizans)cold hardy? Hardiness zone & min temp

Also called Blue Candle Cactus, Whortleberry Cactus, Bilberry Cactus.

More about myrtillocactus geometrizans

About Myrtillocactus geometrizans

Myrtillocactus geometrizans · also called Blue Candle Cactus, Whortleberry Cactus · houseplant

Myrtillocactus geometrizans, the blue candle or bilberry cactus, is a fast, branching Mexican columnar cactus with striking powder-blue, candelabra-like stems and short black spines. It produces small cream flowers and edible blueberry-like fruit. Easy and vigorous indoors, it rewards bright light and gritty, fast-draining soil with handsome ghostly-blue growth.

Cold limit: USDA 9-11 (indoor in most US and UK homes) · RHS H2 (10-35°C)

Watch for — Basal and root rot: Soft, dark base from overwatering or poor drainage. Use gritty mix, let it dry between waterings, and reduce water in winter.

What myrtillocactus geometrizans's hardiness rating actually means

Myrtillocactus geometrizans 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 9-11 (indoor in most US and UK homes) — 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. Myrtillocactus geometrizans shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for myrtillocactus geometrizans 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 myrtillocactus geometrizans go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (indoor in most US and UK homes) 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 myrtillocactus geometrizans 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 myrtillocactus geometrizans

Myrtillocactus geometrizans 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.

Myrtillocactus geometrizans hardiness — frequently asked questions

Is myrtillocactus geometrizans cold hardy?

Myrtillocactus geometrizans 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 9-11 (indoor in most US and UK homes) (and sheltered UK gardens) myrtillocactus geometrizans can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature myrtillocactus geometrizans can survive?

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

What hardiness zone is myrtillocactus geometrizans?

Myrtillocactus geometrizans is rated USDA 9-11 (indoor in most US and UK homes) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can myrtillocactus geometrizans survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (indoor in most US and UK homes) 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 myrtillocactus geometrizans 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.