Cold hardiness & minimum temperature

Is Butternut squash (Cucurbita moschata)cold hardy? Hardiness zone & min temp

Also called butternut pumpkin, gramma.

About Butternut squash

Cucurbita moschata · also called butternut pumpkin, gramma · edible

Butternut is a long-keeping winter squash with sweet orange flesh. More disease-resistant than C. pepo squashes, but slower to mature — needs 110-120 frost-free days. Direct-sow after last frost in rich soil. Pet-safe.

A cultivar of Cucurbita moschata, the moschata group was domesticated in the lowland tropical Americas (Mesoamerica) and is the most heat- and humidity-tolerant of the winter squashes.

Harvest when the rind is hard and a deep, solid tan; unlike thin-skinned pepo squash, butternut benefits from a full 7–14 day cure at 80–85F and develops its best flavor after one to two months of storage.

Cold limit: USDA Grown as an annual in zones 4-11 · RHS H2 (18-29°C)

Sources: plants.ces.ncsu.edu, extension.illinois.edu, en.wikipedia.org

What butternut squash's hardiness rating actually means

Hardiness works differently for butternut squash: 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 H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA Grown as an annual in zones 4-11 — 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 butternut squash 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 butternut squash 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 butternut squash can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline butternut squash

Butternut squash 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.

Butternut squash hardiness — frequently asked questions

Is butternut squash cold hardy?

Hardiness works differently for butternut squash: 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. Butternut squash is grown Grown as an annual in zones 4-11; you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature butternut squash 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 butternut squash?

Butternut squash is rated USDA Grown as an annual in zones 4-11 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can butternut squash 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 butternut squash 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.