How to Grow Pumpkins

What a pumpkin is

“Pumpkin” is a name, not a species. Iowa State uses it for any round, hard-rinded winter squash, usually ribbed and orange, yellow or white. Jack-o’-lantern pumpkins belong to Cucurbita pepo, the same species as zucchini and acorn squash. ‘Dickinson’, the main pumpkin used for canned puree, is C. moschata, like butternut. The giants seen at state fairs, such as ‘Big Max’ and ‘Dill’s Atlantic Giant’, are C. maxima, and cushaws are C. mixta. All of them are grown the same way. The species matters mainly for cooking quality, pest resistance and seed saving.

Timing: work back from the harvest you want

Pumpkins are very tender. Colorado State plants them two or more weeks after the average last frost, and the soil should be at least 60°F at 4 inches deep (Clemson) or 65°F (Utah State).

The bigger question is when you want fruit. Most varieties need 90 to 120 days from seed; UF/IFAS gives 80 to 100 days from seed and 70 to 90 from transplants, and giants such as ‘Big Max’ take about 120. Once a fruit sets, it needs another 45 to 55 days to mature, according to Utah State.

For Halloween, find the days to maturity on the seed packet and count back from early October, then add a week or two of margin, since Iowa State notes that cool weather slows ripening. In the Midwest that usually means sowing in mid- to late May: Iowa State sows in mid-May in central Iowa, 7 to 10 days earlier in the south of the state and 7 to 10 days later in the north, and calls mid-June the last practical date. Farther south, the calendar shifts later. Clemson plants pumpkins from June 15 to July 15 in the South Carolina Piedmont and through June on the coast, so the fruit ripens in fall rather than in late-summer heat.

An early crop is not wasted. Properly cured pumpkins keep 2 to 3 months, so fruit harvested in September still makes it to Halloween if you store it well. The dates for your zone above show the full planting window.

Direct seeding and transplants

Most gardeners sow pumpkins directly in hills, low mounds that Colorado State uses so excess water drains away from the seedlings. Utah State plants 4 to 6 seeds 1 to 2 inches deep per mound and thins to two plants once seedlings have two leaves. Iowa State sows 4 to 5 seeds 1 inch deep and keeps 2 or 3. Cut the extras off at soil level so the remaining roots are not disturbed.

For an earlier start, sow indoors 3 to 4 weeks before your planting date in peat pots or other plantable containers, 3 or 4 seeds per pot thinned to two. Pumpkin seedlings do not tolerate root disturbance, so plant the pot and all. Utah State sets transplants out when they have three or four mature leaves; harden them off outdoors for a few days first.

Black plastic mulch and row covers speed things up in cool areas. Utah State says they let you plant about two weeks before the last frost date. Remove covers when the plants start to flower or the temperature under them passes 90°F, and Clemson stresses that covers must be off during the day once bloom starts so bees can reach the flowers.

Spacing

Pumpkins take room. Plan the bed before you plant; Iowa State points out that good spacing improves airflow and reduces powdery mildew.

• Standard vining pumpkins: Iowa State spaces hills 4 to 5 feet apart in rows 5 to 7 feet apart. Clemson gives large-vined varieties 3 to 5 feet in rows 6 to 8 feet apart.
• Bush or short-vined types: Clemson spaces them 2 to 3 feet apart in rows 3 to 5 feet apart.
• Giants: Utah State allows at least 100 square feet per hill, and Iowa State notes that world-record growers often leave 20 to 25 feet between plants.

Utah State suggests one or two hills per person and expects 25 to 50 fruits per 100 feet of row, depending on size.

Soil, fertilizer and water

Pumpkins grow best in full sun and fertile, well-drained soil rich in organic matter. Clemson recommends a pH of 6.2 to 6.5. Work in compost or well-rotted manure, then fertilize according to a soil test. Without one, Iowa State uses 1 to 2 pounds of 10-10-10 per 100 square feet before planting, and Clemson’s rate of 5-10-10 works out to about 3 pounds per 100 square feet.

Feed again as the vines grow. Utah State side-dresses with 1 to 2 tablespoons of 21-0-0 per plant or mound when vines start to run, worked in at least 6 inches from the stem. Clemson waits until first bloom and applies 2 pounds of calcium nitrate per 100 feet of row, 6 to 8 inches from the plants on both sides. Do not overdo nitrogen: Iowa State warns that high-nitrogen feeding can hold back flowering and fruit growth on giant pumpkins.

Water deeply, 1 to 2 inches a week, ideally with drip or a soaker hose so the leaves stay dry. Clemson says moisture matters most during fruit set and fruit development, and recommends wetting the soil 6 inches deep. Utah State cuts back on water as the fruit ripens. Hold organic mulch until the soil reaches about 75°F; after that it keeps soil moisture even, holds down weeds and keeps fruit off bare ground.

Flowers and pollination

Each pumpkin vine carries separate male and female flowers. The first flowers to open are male, and they drop without making fruit; this is normal. Female flowers, with a miniature pumpkin at the base, open later. Bees must carry pollen from male to female flowers. If a female flower is poorly pollinated, the little fruit starts to grow, then yellows and shrivels.

Iowa State lists the usual causes of poor set: cold, rainy or windy weather that keeps bees away, and insecticides that kill them. If you must spray, do it in the evening when bees are less active. Colorado State suggests hand pollination, moving pollen from a male flower to a female one, when bees are scarce.

Choosing varieties

Extension services recommend these, by use:

• Carving and general use: Utah State recommends ‘Autumn Gold’, ‘Connecticut Field’ and ‘Spirit’ (18 to 25 pounds) for Utah. Clemson’s South Carolina list for carving includes ‘Autumn Gold’, ‘Ghost Rider’, ‘Jack O’Lantern’, ‘Howden’, ‘Magic Lantern’, ‘Merlin’ and ‘Spirit’.
• Pie pumpkins: Clemson recommends ‘Amish Pie’ and ‘Small Sugar’.
• Miniatures: ‘Jack Be Little’, ‘Wee-B-Little’ and ‘Baby Bear’ (half a pound to 1 1/2 pounds) in Utah; ‘Baby Boo’ and ‘Jack Be Little’ in South Carolina.
• White pumpkins: Iowa State lists ‘Lumina’, ‘Cotton Candy’, ‘Silver Moon’, ‘Valenciano’ and ‘Full Moon’ (60 to 90 pounds). White types have the same orange flesh inside.
• Giants: ‘Big Max’ and ‘Big Moon’ can top 200 pounds (Utah State); Clemson notes they are partially resistant to downy mildew. Iowa State adds ‘Dill’s Atlantic Giant’ and ‘Prizewinner’.
• Florida: UF/IFAS recommends ‘Big Max’, ‘Connecticut Field’, ‘Prizewinner’, ‘Jack Be Little’ and ‘Jack O Lantern’, plus tropical pumpkins (calabaza, Seminole and Moranga), which it describes as disease resistant.

Regional growing notes

Cold North and high elevations. The challenge is fitting 100-plus days between frosts. Colorado State says pumpkins are most productive below 5,000 feet. Choose shorter-season varieties, start transplants indoors, and use black plastic and row covers to gain a couple of weeks at the start.

Humid South and Gulf Coast. Disease and fruit rot are the main problems. Clemson lists bacterial wilt, powdery and downy mildew, fruit rot and anthracnose. Plant on the later schedule described above, space generously for airflow, water at the base, and keep fruit off wet soil with mulch. In Florida, UF/IFAS plants pumpkins in early July in the north, mid-July in central Florida and early August in the south, and the tropical calabaza and Seminole types hold up better in the heat and humidity.

Arid West and desert Southwest. In the low desert around Phoenix, the University of Arizona sows pumpkins in March or from July to early August, timing the crop around the hottest weeks. Drip irrigation under mulch is the most efficient way to deliver 1 to 2 inches a week in dry heat and wind.

Warm-winter zones 9 to 11. Pumpkins are a summer-sown, fall-harvested crop here, as the Florida dates show. They do not fit a winter planting the way cucumbers and summer squash do.

Pests and diseases

Squash vine borer. A sudden wilt of a healthy-looking vine in midsummer, with yellow, sawdust-like frass at the base of the stem, means borers. The adult is a red-orange and black, wasp-like moth that flies by day and lays eggs at the base of the stems; the larvae tunnel inside. UConn notes that C. pepo, which includes most carving pumpkins, is highly susceptible, C. maxima giants somewhat less so, and C. moschata least of all. Its suggestions:

• Scout for moths from mid- to late June; a yellow bowl of soapy water near the plants traps them.
• Wrap the base of young stems with foil or nylon before moths appear.
• Use row covers early, but not where squash grew last year, because adults emerge from the soil under the cover.
• If borers get in, slit the stem lengthwise, remove the larvae and bury the wounded section so it can root.
• Vining types that put down roots along their runners can resist or even recover from an infestation.

Insecticides work only before larvae enter the stem. Iowa State times sprays to the base of the vines when moths fly, early to mid-June in Iowa. Iowa State also notes that delaying planting to dodge the moths, which works for zucchini, is not practical for pumpkins because of their long season.

Squash bugs. Gray-brown, 5/8-inch bugs that suck sap until leaves wilt and die. Iowa State and Utah State recommend removing the brick-red egg clusters on leaf undersides, hand-picking adults, and laying boards under the plants to trap them overnight; check the boards each morning. Iowa State notes that small nymphs can be controlled with insecticides such as carbaryl.

Cucumber beetles. These spread bacterial wilt, though the University of Vermont notes that pumpkins are far more tolerant of it than cucumbers. Row covers on young plants give the best protection; remove them at bloom.

Powdery mildew. White powdery spots on leaves appear from midsummer and can whiten whole leaves by fall. Iowa State says it is worst in shade, still air and humid but not rainy weather. When it strips the vines, Utah State notes, fruit is exposed to the sun and ripens prematurely. Grow plants in full sun, space them well, avoid overhead watering and choose resistant varieties. Sulfur-based fungicides applied at the first sign, and repeated, keep it in check.

Rotation and cleanup. Clemson recommends not planting pumpkins where cucumbers, melons or other squash grew for at least three years. Remove and destroy vines after harvest so squash bugs and borers have nowhere to overwinter.

Growing a giant pumpkin

Start with a giant variety, a sunny, well-drained site with lots of manure worked in, and a hose within reach. Utah State plants 6 to 8 seeds per hill and keeps the best one or two plants, removes the first two or three female flowers so the vine builds more leaf area, then lets only one fruit develop. Iowa State instead keeps two or three fruits on separate runners at first and removes all others. Both stress steady water, about an inch a week according to Iowa State, regular feeding with a complete fertilizer, and tight pest control.

Harvest, curing and storage

A pumpkin is ready when it is deeply and evenly colored, the rind resists a fingernail, and the vines are dying back. Harvest all mature fruit before a hard freeze; a light frost kills the vines but leaves mature fruit unharmed.

Cut, do not twist, the fruit from the vine with pruners or loppers, leaving a 3- to 4-inch stem. Pumpkins with a stem attached rot less, and Clemson advises against harvesting fruit while it is wet. Never carry a pumpkin by its stem, which may not hold the fruit’s weight and can snap off.

Iowa State washes fruit with soapy water or a 10 percent bleach solution to remove rot organisms; Clemson uses a weaker dip of 4 teaspoons of bleach per gallon. Then cure the pumpkins at 80 to 85°F and high humidity for about 10 days to harden the rind and heal small wounds. The University of Vermont says curing also raises sugar content, and that 5 to 10 days in a ventilated spot out of the sun works if you cannot reach 80°F, as long as it stays above 60°F.

Store cured pumpkins at 50 to 55°F in a single layer, not touching, with good air movement and moderate humidity: 50 to 75 percent according to Clemson. Keep them away from apples and pears, whose ethylene gas shortens storage life, and protect them from temperatures below 50°F or above 95°F. Check them now and then and remove any that soften. Well-cured pumpkins keep 2 to 3 months.