Cold hardiness & minimum temperature

Is Nettleleaf Giant Hyssop (Agastache urticifolia)cold hardy? Hardiness zone & min temp

Also called Nettleleaf Giant Hyssop, Nettle-leaved Horsemint, Horse Mint.

More about nettleleaf giant hyssop

About Nettleleaf Giant Hyssop

Agastache urticifolia · also called Nettleleaf Giant Hyssop, Nettle-leaved Horsemint · herb

A tall, robust native North American perennial wildflower found in moist mountain meadows and open woodlands from the Rocky Mountains to the Pacific Northwest. It bears showy rose-lavender flower spikes through summer, attracting bees, butterflies, and hummingbirds. The anise-scented leaves were used medicinally by indigenous peoples. Excellent for naturalistic and native plantings.

Cold limit: USDA 4–8 · RHS H6 (−20°C to 32°C)

What nettleleaf giant hyssop's hardiness rating actually means

Yes — nettleleaf giant hyssop is genuinely cold hardy. Rated RHS H6 and USDA 4–8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 4–8 — 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 −20 to −15 °C. Nettleleaf Giant Hyssop is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for nettleleaf giant hyssop as it gets too cold:

It tolerates winter lows to about −20 to −15 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can nettleleaf giant hyssop go outside or overwinter — and where?

Plant it out within USDA 4–8 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

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 nettleleaf giant hyssop can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Nettleleaf Giant Hyssop hardiness — frequently asked questions

Is nettleleaf giant hyssop cold hardy?

Yes — nettleleaf giant hyssop is genuinely cold hardy. Rated RHS H6 and USDA 4–8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Nettleleaf Giant Hyssop is hardy across USDA 4–8; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature nettleleaf giant hyssop can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Nettleleaf Giant Hyssop is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is nettleleaf giant hyssop?

Nettleleaf Giant Hyssop is rated USDA 4–8 and RHS H6 — Hardy throughout the UK and northern Europe.

Can nettleleaf giant hyssop survive winter outside?

Plant it out within USDA 4–8 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to nettleleaf giant hyssop below its minimum temperature?

It tolerates winter lows to about −20 to −15 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.