Cold hardiness & minimum temperature

Is Sweet pea (Lathyrus odoratus)cold hardy? Hardiness zone & min temp

Also called annual sweet pea, garden sweet pea.

About Sweet pea

Lathyrus odoratus · also called annual sweet pea, garden sweet pea · flowering

Sweet peas are cool-season climbing annuals grown for fragrant ruffled flowers in every colour but yellow. Need cool roots, support, and constant deadheading. Toxic to pets — and the seeds are toxic to people too; never confuse with edible peas.

Sweet pea (Lathyrus odoratus) is a climbing annual legume from the central Mediterranean (Sicily and southern Italy), prized above all for the strong fragrance bred into many cultivars.

Sow in autumn or spring; regular cutting and deadheading prolong bloom. Pods and seeds are not edible and may cause stomach upset, so wear gloves when handling.

Cold limit: USDA Grown as an annual in zones 2-11 · RHS H3 (10-21°C)

Sources: rhs.org.uk, rhs.org.uk, missouribotanicalgarden.org

What sweet pea's hardiness rating actually means

Hardiness works differently for sweet pea: 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 Grown as an annual in zones 2-11 — 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 sweet pea 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 sweet pea 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 sweet pea 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 sweet pea

Sweet pea 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.

Sweet pea hardiness — frequently asked questions

Is sweet pea cold hardy?

Hardiness works differently for sweet pea: 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. Sweet pea is grown Grown as an annual in zones 2-11; you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature sweet pea 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 sweet pea?

Sweet pea is rated USDA Grown as an annual in zones 2-11 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can sweet pea 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 sweet pea 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.