Cold hardiness & minimum temperature

Is Ribbed Melilot (Melilotus officinalis)cold hardy? Hardiness zone & min temp

Also called Ribbed Melilot, Yellow Melilot, Yellow Sweet Clover, Common Melilot.

More about ribbed melilot

About Ribbed Melilot

Melilotus officinalis · also called Ribbed Melilot, Yellow Melilot · herb

Melilotus officinalis is a tall, erect biennial or short-lived perennial legume native to Eurasia, widely naturalised in the UK, US, and Canada on roadsides, waste ground, and disturbed soils. It prefers free-draining, neutral to alkaline soils in full sun and is notably drought-tolerant once established, fixing atmospheric nitrogen via root nodules. The critical safety note is that coumarin in the foliage converts to the anticoagulant dicoumarol when the plant is improperly dried or allowed to mould — this is toxic to livestock and potentially pets, making it mildly toxic.

Cold limit: USDA 4-9 · RHS H6 (-15–30°C)

What ribbed melilot's hardiness rating actually means

Yes — ribbed melilot is genuinely cold hardy. Rated RHS H6 and USDA 4-9, 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 4-9 — 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 −20 to −15 °C. Ribbed Melilot is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for ribbed melilot 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 ribbed melilot go outside or overwinter — and where?

Plant it out within USDA 4-9 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 ribbed melilot can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Ribbed Melilot hardiness — frequently asked questions

Is ribbed melilot cold hardy?

Yes — ribbed melilot is genuinely cold hardy. Rated RHS H6 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Ribbed Melilot is hardy across USDA 4-9; 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 ribbed melilot can survive?

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

What hardiness zone is ribbed melilot?

Ribbed Melilot is rated USDA 4-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can ribbed melilot survive winter outside?

Plant it out within USDA 4-9 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 ribbed melilot 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.