Cold hardiness & minimum temperature

Is Cuphea hyssopifolia (Cuphea hyssopifolia)cold hardy? Hardiness zone & min temp

Also called false heather, elfin herb, Mexican heather.

More about cuphea hyssopifolia

About Cuphea hyssopifolia

Cuphea hyssopifolia · also called false heather, elfin herb · flowering

False heather is a compact evergreen subshrub with fine, glossy needle-like foliage and a constant scatter of tiny lavender, pink or white flowers. Native to Mexico and Central America, it thrives in heat and full sun, working as a tidy low hedge, edging or container plant and blooming almost year-round in frost-free climates.

Cold limit: USDA 9-11 (evergreen; root-hardy at the warm edge of zone 8, grown as an annual colder) · RHS H1c (18-29°C)

Watch for — Frost damage: Tender to cold; foliage browns and dies back below freezing. Mulch roots and overwinter in containers indoors in zones colder than 9.

What cuphea hyssopifolia's hardiness rating actually means

Hardiness works differently for cuphea hyssopifolia: 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 H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 9-11 (evergreen; root-hardy at the warm edge of zone 8, grown as an annual colder) — 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 cuphea hyssopifolia 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 cuphea hyssopifolia 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 cuphea hyssopifolia can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Frost protection for borderline cuphea hyssopifolia

Cuphea hyssopifolia 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.

Cuphea hyssopifolia hardiness — frequently asked questions

Is cuphea hyssopifolia cold hardy?

Hardiness works differently for cuphea hyssopifolia: 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. Cuphea hyssopifolia is grown 9-11 (evergreen; root-hardy at the warm edge of zone 8, grown as an annual colder); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature cuphea hyssopifolia 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 cuphea hyssopifolia?

Cuphea hyssopifolia is rated USDA 9-11 (evergreen; root-hardy at the warm edge of zone 8, grown as an annual colder) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can cuphea hyssopifolia 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 cuphea hyssopifolia 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.