Cold hardiness & minimum temperature

Is Acorn squash (Cucurbita pepo)cold hardy? Hardiness zone & min temp

Also called pepper squash, Des Moines squash.

About Acorn squash

Cucurbita pepo · also called pepper squash, Des Moines squash · edible

Acorn squash is a small dark-green winter squash with ribbed fruit and sweet orange flesh. Bush and vining types are available. Easier than long-keeping squash and ready in 80-100 days. Pet-safe.

A Cucurbita pepo winter squash; C. pepo was independently domesticated in the Americas and includes acorn, delicata, spaghetti, and the summer squashes.

Matures in roughly 80–100 days; harvest when rind is hard and ground spot orange. Acorn is one of the few squashes that should NOT be heat-cured — high-heat curing turns C. pepo flesh stringy and shortens storage, so move it straight to cool (50–55F) storage and use within 1–2 months.

Cold limit: USDA Grown as an annual in zones 3-10 · RHS H2 (18-29°C)

Sources: extension.illinois.edu, ucanr.edu

What acorn squash's hardiness rating actually means

Hardiness works differently for acorn 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 3-10 — 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 acorn 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 acorn 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 acorn 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 acorn squash

Acorn 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.

Acorn squash hardiness — frequently asked questions

Is acorn squash cold hardy?

Hardiness works differently for acorn 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. Acorn squash is grown Grown as an annual in zones 3-10; you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature acorn 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 acorn squash?

Acorn squash is rated USDA Grown as an annual in zones 3-10 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can acorn 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 acorn 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.