Cold hardiness & minimum temperature

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

Also called yellow monkeyflower, common monkeyflower, seep monkeyflower.

More about yellow monkeyflower

About Yellow Monkeyflower

Mimulus guttatus · also called yellow monkeyflower, common monkeyflower · flowering

Yellow Monkeyflower is a cheerful, short-lived perennial native to moist stream banks and seepages across western North America. Bright yellow, snapdragon-like flowers often spotted with red bloom freely from early summer to autumn. It grows at pond margins in up to 10–15 cm of water and attracts bees and hoverflies. No known toxicity.

Cold limit: USDA 5-9 · RHS H4 (-10–25°C)

Watch for — Short lifespan / die-back: Mimulus guttatus is short-lived and may not persist beyond 2–3 years in cold or wet winters. It self-seeds freely around pond margins, usually self-renewing; collect seed in autumn as insurance.

What yellow monkeyflower's hardiness rating actually means

Yes — yellow monkeyflower is genuinely cold hardy. Rated RHS H4 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 5-9 — 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 −10 to −5 °C. Yellow Monkeyflower is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for yellow monkeyflower as it gets too cold:

It tolerates winter lows to about −10 to −5 °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 yellow monkeyflower go outside or overwinter — and where?

Plant it out within USDA 5-9 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 yellow monkeyflower can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Yellow Monkeyflower hardiness — frequently asked questions

Is yellow monkeyflower cold hardy?

Yes — yellow monkeyflower is genuinely cold hardy. Rated RHS H4 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Yellow Monkeyflower is hardy across USDA 5-9; 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 yellow monkeyflower can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Yellow Monkeyflower is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is yellow monkeyflower?

Yellow Monkeyflower is rated USDA 5-9 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can yellow monkeyflower survive winter outside?

Plant it out within USDA 5-9 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 yellow monkeyflower below its minimum temperature?

It tolerates winter lows to about −10 to −5 °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.