Pumpkin, Squash, and Gourds

Introduction 

In the U.S., the cultivated members of the Cucurbita genus fall into three species: Cucurbita pepo (pumpkins, summer squashes, and some winter squashes), C. maxima (buttercup and Hubbard squashes, and giant pumpkins), and C. moschata (butternut squashes). With the exception of C. maxima, whose center of origin is in South America, it is assumed that the other cultivated species were domesticated in Mesoamerica. The catch-all term "gourd" includes some members of the genus Cucurbita as well as some members of the genus Lagenaria.

Squash, pumpkins, and some gourds can be marketed for a variety of purposes: as a vegetable or for seeds; as an ingredient in pies, cakes, and pastries; and as a base for cold and warm soups. Many types, edible and inedible, are marketed for their ornamental value.

Types and Varieties

There are several types of summer squashes which vary in size and shape, including: zucchini, yellow and yellow crookneck, patty pan, cousa, as well as spherical types such as ‘Eight Ball’. These are harvested every 1–3 days, often from 2–3 sequential plantings throughout the season. Winter squash come in diverse shapes and sizes, from very large to very small, and are harvested once at the end of the season. Pumpkins also range from small to very large. They can have smooth, rough, or warty textures and come in white, orange, yellow, deep red, and various mottled colors. Note that the so-called giant pumpkins are actually C. maxima, unlike standard pumpkins, which are C. pepo. Of the cucurbits, gourds are most known for their colors and shapes. Many bear names that reflect their appearance: crook-necked, winged, crown-of-thorns.

Types and Varieties of Pumpkins

Types and Varieties of Squash

Types and Varieties of Gourds

Soil Fertility

Apply lime according to soil test results to maintain soil pH at 6.5–6.8. Pumpkins and squash prefer well-drained soil, preferably sandy loams with high organic matter. Gourds can be grown in a wide range of soil types but mature earlier and color better on sandy soils or sandy loams that drain well and warm up early in the spring. Squashes and pumpkins are relatively heavy feeders.

Plant Nutrient Recommendations According to Soil Test Results for Pumpkin and Squash

Planting

Direct Seeding. Earlier planting may result in earlier harvest, but plastic mulch, row covers, raised beds, and transplants may be necessary to overcome cold-temperature conditions. Squash, pumpkins, and gourds should not be planted until after there is no danger of frost. While optimum soil temperature for germination is about 85ºF, minimum soil temperature should be 65ºF for direct-seedings, warmer if using untreated seed. Germination may take 5–10 days, depending on soil temperature. Seeds are planted at 0.75"–1” in heavier soils, and 1"–1.5” in lighter soils. Squash seeds are prone to rot in excessively wet conditions, so adjust depth accordingly.

Transplanting. In locations where the soil is slow to warm or there are insurmountable insect or rodent problems, transplanting 3-week-old seedlings is an option. Cucurbit roots are sensitive to cold soils. Root damage during removal from cell trays and transplanting must be kept to an absolute minimum. For this reason, growers often start cucurbit seeds in degradable pots that can be set directly into the field. When planting through plastic mulch, stems must not be abraded by the edge of the hole in the plastic. Leggy transplants have a lower survival rate than compact, younger seedlings.

Spacing. Plant population and spacing depend on plant growth habits and desired fruit sizes. Compact or bush-type squashes can be spaced 18"–24” apart within rows, and 3'–5’ between rows, depending on available space and accommodation for machinery. Compact squashes, particularly summer-harvested types, are typically planted through black plastic mulch for soil warmth, weed suppression, and soil moisture consistency. Well-drained soils should also have drip tape under the mulch. Vining squashes are usually not planted through plastic mulch, although on a small scale and/or on organic farms it is practical and will save labor and improve yield. These vining plants usually require 5'–6’ between rows, with plants spaced at 18"–30”, depending on desired fruit size. Direct-seed heavily to allow for rodent damage and poor germination. Thinning can take place a few weeks after seeding.

Field Culture

Reduced Tillage. Pumpkins and winter squash can also be produced in strip-till or no-till systems. Seeds are planted into the stubble of a killed cover crop or harvested small grain. Herbicide may be necessary. Reduced-till systems provide erosion control, help retain soil moisture, improve soil structure, reduce weed and disease pressure, provide cleaner fruit at harvest, and may facilitate planting and harvest operations during wet weather.

Pollination. Pumpkin and squash require bee activity for good fruit set. Fruit set in winter squash and pumpkin takes place largely over a 2- to 3-week period, while summer squash pollination takes place throughout the summer, depending on cropping sequence. Inadequate pollination results in poorly shaped fruit and excessive blossom drop. Your location may have good populations of wild bees, including native bumblebees and squash bees. Make observations to determine whether or not you need to supplement with hives. One hive of bees per acre is recommended. If honey bees are not available, bumble bees are a reliable alternative and are commercially available. Since bees can carry pollen for a mile or more, isolation of fields from other types of squash or pumpkin is rarely possible in the New England area. 

Several factors other than bees and pollination may affect fruit set. Pumpkins and squash have separate male and female flowers. The numbers of female flowers, which produce fruit, is adversely affected by prolonged periods of high temperatures (more than 7 days above 90º F in the day and 70º F at night), dry conditions just prior to and during bloom, excessive soil nitrogen, and excessive shading from the plant canopy. Sometimes low yields associated with lack of female flowers can be avoided or minimized by making several plantings over 2–3 weeks, planting several varieties, timely irrigation, and spacing pumpkins farther apart to help reduce shading.

Harvest and Storage

Summer squash should be harvested when fully expanded but still immature, while the rind is still glossy and easily scratched by a fingernail. This may require a 1- to 3-day picking interval. Zucchini may be harvested by cutting the stem with a knife, while straight-neck and crookneck can be twisted from the plant. Spines on the petioles can easily damage the surface of fruits, so they should be pulled out of the plant canopy carefully. Cutting with a knife can transmit viruses. If virus is detected in the field, fruit should be harvested by twisting from the plant. 

Summer squash can be damaged from 3–4 days of exposure to temperatures of 32ºF–40ºF and 90% or higher relative humidity. This is commonly referred to as "chilling injury". If storage is required, hold at 45ºF–50ºF and at 90% relative humidity for up to 2 weeks. Summer squash should be marketed as soon as possible.

Winter Squash and Pumpkin. For winter squash, good yields of smaller varieties are 5–7 tons or 2,000–4,000 fruit per acre. The large types (fresh market) may yield up to 10–30 tons or 1,000–2,000 fruit per acre. Squash is mature when seeds are completely filled. If squash is harvested before it is mature, the fruit will use starch reserves from the flesh to fill the seeds, resulting in poor flesh quality. Immature squash will also not have enough starch to convert into sugar later on. Most squash varieties are mature and ready to harvest 50–55 days after fruit set, or days after pollination. In many varieties, this is many weeks after the fruit turns a marketable color, which can be misleading. Winter squash and pumpkin are not normally harvested until the rind or skin is completely hardened. If necessary, pumpkins can be harvested as soon as some color is present. If possible, pumpkins that have reached full color should be stored under cover to protect them from chilling injury from temperatures below 50ºF and from disease. Fruits are easily damaged by rough handling. Do not permit fruits to be exposed to 32ºF, as this can promote storage problems.

Winter squash should be well-matured for storage, and free from injury or decay. A 5- to 10-day curing period at 80ºF–85ºF before storage is necessary for C. maxima and C. moschata types, but C. pepo types can be eaten right away and do not benefit from curing. For the longer term, winter squash should be stored at 55ºF–60ºF and 50%–75% relative humidity. Chilling injury occurs any time the temperatures fall below 55ºF, either in the field or in storage. Damage is cumulative; injury increases as temperature decreases and/or length of chilling time increases. Fruit that has experienced chilling injury is likely to break down in storage.

Pumpkin can be stored in good condition for 2–3 months at 50ºF–55ºF and 50%–70% relative humidity. Hubbard and butternut squash can be kept 6 months or more, acorn 5–8 weeks, and buttercup 2–3 months or more. Squash should not be stored with ethylene producers such as ripe apples or pears, since squash will turn color, become stringy, and decay. It is important to keep squash dry and maintain good air circulation.

Gourds. Gourds should mature between late summer and the first fall frost. Harvest fruit when the stems become dry and the skin is hard. Discard any fruit which is bruised, cut, or showing symptoms of disease. Wash gourds in warm, soapy water to remove any soil and reduce postharvest rots.

Rinse fruit in clean water and dry with a soft cloth. Spread the gourds out on several layers of newspaper in a warm, dry place, such as an attic or loft, for final drying. This should take 3–4 weeks.

Dried gourds may be marketed in their natural state or treated with a protective, shiny coating. Gourds may be waxed with a paste-type wax and buffed with a soft cloth, or shellac may be applied by spraying, brushing, or dipping to give them a hard, glossy finish.