Cold hardiness & minimum temperature

Is Narrow-leaved Everlasting Pea (Lathyrus sylvestris)cold hardy? Hardiness zone & min temp

Also called Narrow-leaved Everlasting Pea, Flat Pea, Narrow-leaved Vetchling, Wood Pea.

More about narrow-leaved everlasting pea

About Narrow-leaved Everlasting Pea

Lathyrus sylvestris · also called Narrow-leaved Everlasting Pea, Flat Pea · flowering

Narrow-leaved Everlasting Pea is a robust, long-lived climbing perennial native to woodland edges, scrub, hedgerows, and rough grassland across England and much of temperate Europe. It climbs by tendrils and produces racemes of 4–10 rose-pink to purple-pink flowers blotched with green from June to August, making it a striking addition to a wildlife garden fence or trellis. The most critical care requirement is providing a sturdy support structure, as the winged stems can reach 2 m or more and will otherwise form an unruly mat. Seeds and plant tissues contain lathyrogen amino acids (BAPN) that cause lathyrism in horses; ASPCA lists the genus as mildly concerning, with primary toxicity recorded for horses rather than dogs and cats.

Cold limit: USDA 5-9 · RHS H6 (-20°C to 25°C)

What narrow-leaved everlasting pea's hardiness rating actually means

Yes — narrow-leaved everlasting pea is genuinely cold hardy. Rated RHS H6 and USDA 5-9, 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 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 −20 to −15 °C. Narrow-leaved Everlasting Pea is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for narrow-leaved everlasting pea 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 narrow-leaved everlasting pea 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 narrow-leaved everlasting pea can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Narrow-leaved Everlasting Pea hardiness — frequently asked questions

Is narrow-leaved everlasting pea cold hardy?

Yes — narrow-leaved everlasting pea is genuinely cold hardy. Rated RHS H6 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Narrow-leaved Everlasting Pea 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 narrow-leaved everlasting pea can survive?

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

What hardiness zone is narrow-leaved everlasting pea?

Narrow-leaved Everlasting Pea is rated USDA 5-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can narrow-leaved everlasting pea 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 narrow-leaved everlasting pea 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.