Cold hardiness & minimum temperature

Is Leek (Allium ampeloprasum var. porrum 'Musselburgh')cold hardy? Hardiness zone & min temp

Also called Musselburgh leek, leek.

More about leek

About Leek

Allium ampeloprasum var. porrum 'Musselburgh' · also called Musselburgh leek, leek · edible

The leek is a hardy, long-season allium grown for its thick blanched white shaft of tightly wrapped leaf bases. 'Musselburgh' is a classic dependable Scottish heritage variety, very cold-tolerant and standing well through winter for harvest from autumn into early spring. Plants are dropped into deep dibber holes and earthed up to lengthen and whiten the edible stem.

Cold limit: USDA 5-10 (very hardy; overwinters in milder zones) · RHS H5 (7-24°C)

What leek's hardiness rating actually means

Hardiness works differently for leek: 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 H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 5-10 (very hardy; overwinters in milder zones) — 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 leek 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 leek 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 leek can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Frost protection for borderline leek

Leek 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.

Leek hardiness — frequently asked questions

Is leek cold hardy?

Hardiness works differently for leek: 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. Leek is grown as an annual in USDA 5-10 (very hardy; overwinters in milder zones); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature leek 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 leek?

Leek is rated USDA 5-10 (very hardy; overwinters in milder zones) and RHS H5 — Hardy in most of the UK and in cold winters.

Can leek 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 leek 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.