Cold hardiness & minimum temperature

Is Monkeyflower (Mimulus guttatus)cold hardy? Hardiness zone & min temp

Also called Monkeyflower, Common Monkeyflower, Yellow Monkey Flower, Seep Monkeyflower.

More about monkeyflower

About Monkeyflower

Mimulus guttatus · also called Monkeyflower, Common Monkeyflower · flowering

Mimulus guttatus is a short-lived herbaceous perennial native to moist stream banks, seeps, and wet meadows across western North America, now naturalised in the British Isles where it can be invasive near waterways. It demands consistently wet to waterlogged soil and full sun to light shade, producing bright yellow trumpet-shaped flowers spotted red in the throat from late spring through summer. The key care priority is never letting the soil dry out — even brief drought causes rapid wilting and collapse. Toxicity to cats and dogs is not confirmed by the ASPCA; treat with caution.

Cold limit: USDA 3-10 · RHS H5 (-20°C to 25°C)

What monkeyflower's hardiness rating actually means

Yes — monkeyflower is genuinely cold hardy. Rated RHS H5 and USDA 3-10, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 3-10 — 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 −15 to −10 °C. Monkeyflower is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for monkeyflower as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 monkeyflower go outside or overwinter — and where?

Plant it out within USDA 3-10 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 monkeyflower can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Monkeyflower hardiness — frequently asked questions

Is monkeyflower cold hardy?

Yes — monkeyflower is genuinely cold hardy. Rated RHS H5 and USDA 3-10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Monkeyflower is hardy across USDA 3-10; 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 monkeyflower can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Monkeyflower is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is monkeyflower?

Monkeyflower is rated USDA 3-10 and RHS H5 — Hardy in most of the UK and in cold winters.

Can monkeyflower survive winter outside?

Plant it out within USDA 3-10 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 monkeyflower below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.