How to Grow Winter Squash

Types of winter squash

Winter squash are picked fully mature, with hard rinds and seeds, which is why they store. They come from three species. Acorn and spaghetti squash are Cucurbita pepo, the same species as zucchini and jack-o’-lantern pumpkins. Butternut is C. moschata. Buttercup, Hubbard and banana squash are C. maxima. The species affects storage life and how well the plants stand up to squash vine borers.

When and how to plant

Winter squash is very tender. Colorado State plants it about two weeks or more after the last frost, once days stay above 55°F and the soil at 2 inches is at least 60°F. Because it needs 85 to 120 days, the late limit matters as much as the early one: Iowa State plants from mid-May in central Iowa and says winter squash must be in by June 10. The dates for your zone above show your window.

Sow 4 to 6 seeds 1 to 2 inches deep per hill and thin to the two strongest seedlings (Utah State), or 4 to 5 seeds 1 inch deep thinned to 2 or 3 (Iowa State). Iowa State spaces hills 4 to 5 feet apart in rows 5 to 7 feet apart. Clemson gives large vining types 3 to 5 feet in rows 6 to 8 feet apart, and bush or short-vined types 2 to 3 feet in rows 3 to 5 feet apart. Iowa State notes that semi-bush varieties are available for small gardens.

In short-season areas, start seeds 3 to 4 weeks ahead in peat pots or other plantable containers (Iowa State); Colorado State prefers transplants no older than 2 to 3 weeks, since squash roots do not tolerate disturbance.

Regional timing

North and high elevations. Fit the variety to your season. Acorn types need about 55 to 60 days from flowering to maturity, butternut 60 to 70 and Hubbard 80 to 90, according to Iowa State, and cool weather slows all of them. Colorado State notes that winter squash is most productive below 5,000 feet.

South. Clemson plants winter squash from April 15 to June 15 in the South Carolina Piedmont and March 20 to May 1 on the coast, where a second planting in August is also possible.

Desert Southwest. The University of Arizona sows in March or from July to early August in the Phoenix area.

Warm-winter zones 9 to 11. UF/IFAS plants winter squash from February to April and again in August and September in North Florida, January to April and August to September in Central Florida, and August to March in South Florida.

Varieties

• Utah (Utah State): ‘Pink Banana’ (25 to 40 pounds), ‘Early Butternut’ and ‘Table Ace’.
• South Carolina (Clemson): ‘Early Butternut’, ‘Cornell’s Bush Delicata’ and ‘Table Ace’.
• Iowa (Iowa State): ‘Blue Hubbard’, ‘Burgess Buttercup’, ‘Butternut Supreme’, ‘Sweet Mama’ (buttercup), ‘Table Ace’ and ‘Table Queen’ (acorn), and spaghetti squash.
• Florida (UF/IFAS): spaghetti, ‘Table King’, ‘Table Queen’ and ‘Table Ace’ (acorn), ‘Waltham’ and ‘Early Butternut’.

Care

Squash grows best in full sun and fertile, well-drained soil. Utah State works in up to 2 inches of compost or 4 to 6 cups of all-purpose fertilizer such as 10-10-10 per 100 square feet before planting, then side-dresses with 3 to 4 tablespoons of 21-0-0 per plant when the vines start to run.

Water deeply, 1 to 2 inches a week, with drip if possible, and keep leaves and fruit dry. Utah State cuts back on water as the fruit ripens to reduce fruit rot. Hold organic mulch until the soil reaches about 75°F. Bees must pollinate the female flowers, so if you use row covers against early insects, remove them when flowering starts.

Pests and diseases

Squash vine borer larvae tunnel into stems near the soil, causing sudden wilting. UConn ranks butternut and other C. moschata squash least susceptible because of their thicker, more succulent stems, Hubbard and other C. maxima types more so, and C. pepo types such as acorn the most. If borers have been a problem, butternut is the safest choice. Iowa State notes that ‘Blue Hubbard’ is so attractive to the moths that commercial growers plant it as a trap crop, though most home gardens lack the space. Protect stems with foil wraps or row covers early in the season, and remove infested plants.

Squash bugs wilt leaves with their feeding. Hand-pick adults and egg clusters and trap them under boards. Cucumber beetles spread bacterial wilt; row covers protect young plants. Powdery mildew whitens leaves from midsummer; full sun, good spacing and resistant varieties help.

Clemson recommends waiting at least three years before planting squash where cucumbers, melons or other squash grew, and clearing vines after harvest.

Harvest, curing and storage

Winter squash is ripe when the rind is too hard to pierce with a thumbnail, the skin has gone from glossy to dull with solid color for its type, and the vines start to die back. Spaghetti squash turns from ivory to golden yellow. Harvest everything before a hard freeze. Cut fruit from the vine with about an inch of stem; Iowa State warns that squash with no stem left will not store well.

Cure all types except acorn at 80 to 85°F and 80 to 85 percent humidity for about 10 days to harden the rind and heal scratches. The University of Vermont adds that curing raises sugar content, improving flavor.

Store cured squash at 50 to 55°F in a dry, well-ventilated place away from apples and pears. Expected storage life:

• Acorn: 5 to 8 weeks (Iowa State)
• Butternut: 2 to 3 months (Iowa State) or up to 3 to 4 months (University of Vermont)
• Hubbard and buttercup: 4 to 6 months (University of Vermont); Iowa State gives Hubbard 5 to 6 months

Check stored squash monthly and use any that soften or show spots first.