Cold hardiness & minimum temperature

Is Monkey flower (Mimulus × hybridus)cold hardy? Hardiness zone & min temp

Also called Monkey flower, Hybrid monkey flower, Musk flower.

More about monkey flower

About Monkey flower

Mimulus × hybridus · also called Monkey flower, Hybrid monkey flower · flowering

Hybrid monkey flowers are cool-season annuals bearing tubular, snapdragon-like blooms in vivid reds, oranges, yellows, and bicolours, often marked with contrasting spots. They excel in cool, moist conditions in spring and early summer, making them ideal for shady borders, pots, and streamside plantings. They tend to decline in summer heat but can be revived in autumn.

Cold limit: USDA 6–9 (as a cool-season annual or short-lived perennial) · RHS H3 (5–21°C)

Watch for — Heat collapse and summer dormancy: Hybrid monkey flowers are bred for cool seasons and shut down or die back when temperatures consistently exceed 24–27°C. This is normal — cut back spent stems, reduce watering and feeding, and many plants will regenerate in autumn when temperatures drop.

What monkey flower's hardiness rating actually means

Hardiness works differently for monkey flower: 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 H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 6–9 (as a cool-season annual or short-lived perennial) — 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 monkey flower 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 monkey flower 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 monkey flower can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline monkey flower

Monkey flower 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.

Monkey flower hardiness — frequently asked questions

Is monkey flower cold hardy?

Hardiness works differently for monkey flower: 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. Monkey flower is grown 6–9 (as a cool-season annual or short-lived perennial); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature monkey flower 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 monkey flower?

Monkey flower is rated USDA 6–9 (as a cool-season annual or short-lived perennial) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can monkey flower 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 monkey flower 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.