Yard and Garden: Winter squash
The arrival of autumn also means the arrival of winter squash at the grocery store, farmers market and in the home garden. Winter squash are popular and healthy vegetables providing vitamins A and C as well as fiber. In this article, horticulturists with Iowa State University Extension and Outreach answer commonly asked questions about winter squash in the home garden.
What are winter squash?
Winter squash are members of the cucurbit family, which includes squash, gourds, melons and cucumbers. They are warm-season vegetables that produce long sprawling vines with fruit that typically matures late in the growing season. Unlike summer squash which are harvested and used immature, winter squash are harvested when the fruit fully matures and most can be easily stored for much of the winter.
The term “winter squash” describes varieties of several different edible squash species. Acorn, delicata and spaghetti squash varieties are from the Cucurbita pepo species. Cucurbita moschata includes the butternut types. Many other winter squash belong to the Cucurbita maxima species including Hubbard, kabocha, buttercup and turban squash.
What is the proper way to harvest and store winter squash?
Harvest winter squash when the fruit are fully mature. Mature winter squash have very hard skins that can’t be punctured with the thumbnail and have dull-looking surfaces. Ideally, leave the squash on the vine until fully ripe. It can be difficult to ripen winter squash once harvested. While a light frost may kill the vines, it will not typically harm the fruit, but be sure to harvest winter squash before a hard freeze.
When harvesting winter squash, handle them carefully to avoid cuts and bruises. These injuries are not only unsightly, but they also provide entrances for various rot-producing organisms. Cut the fruit off the vine with pruning shears. Leave a 1-inch stem on each fruit.
After harvesting, cure winter squash (except for the acorn types) at a temperature of 80 to 85 degrees Fahrenheit and relative humidity of 80 to 85%. Curing helps to harden the squash skins and heal any cuts and scratches. Do not cure acorn squash. The high temperature and relative humidity during the curing process reduces the quality and storage life of acorn squash.
After curing, store winter squash in a cool, dry, well-ventilated location. Storage temperatures should be 50 to 55F. Place them in a single layer where they don’t touch one another. Do not pile squash as piling can reduce air circulation, promote moisture build-up which encourages fungi and bacteria and generate excess heat that will shorten the storage life. Do not store squash near apples, pears or other ripening fruit. Ripening fruit release ethylene gas, which shortens the storage life of squash.
When properly cured and stored, the storage lives of acorn, butternut and Hubbard squash are approximately 5 to 8 weeks, 2 to 3 months and 5 to 6 months, respectively.
Will other squash or melons cross-pollinate with winter squash?
Winter squash belong to the same genus (Cucurbita) as many other commonly grown vegetables including summer squash, gourds, melons and cucumbers. Their flowers require pollinators to carry pollen from male to female flowers to form fruit. Only pollen from the same species of Cucurbita can pollinate female flowers and successfully produce fruit. For example, cross-pollination could occur between acorn squash and ornamental gourds because they are both in the species, Cucurbita pepo. However, cross-pollination cannot happen between an acorn squash (C. pepo) and Hubbard squash (C. maxima), muskmelon (C. melo) or cucumber (C. sativus) because they are different species.
Even when cross-pollination occurs, the effects are not seen in the current season’s crop. The squash will still look and taste like the squash described on the seed packet. However, if the seeds are saved and planted the following year, those plants will produce fruit that will be different from either of the parents, often looking like a hybrid of the two.
Poorly flavored squash, melons or cucumbers are usually due to unfavorable soil, moisture or weather conditions, not the result of cross-pollination.
Are pumpkins considered winter squash?
Yes. “Pumpkin” is a general term used to describe any winter squash that has a hard rind, is typically ribbed and roughly round in shape with orange to yellow (sometimes white) skin. There are several species and varieties of winter squash that fit this description. That means the common name of pumpkin is used for several different species of winter squash.
Cucurbita pepo includes field pumpkins often used for jack-o-lanterns, as well as many miniature and sugar or pie-type pumpkins. Cucurbita maxima includes the flattened, deeply ribbed Cinderella-type pumpkins as well as the super-sized pumpkins you see at the state fair. Many of the colorful, and sometimes pumpkin-shaped, cushaw-type squashes are in the species Cucurbita mixta.
I’ve heard canned pumpkin is actually squash, is that true?
Yes. Very few of the species and varieties of winter squash that look like pumpkins (orange, ribbed, round) are used for canned pumpkin puree. Instead, most canned pumpkin is actually made from a species of squash that is not very pumpkin-like.
The species of winter squash most commonly associated with the name pumpkin and used for jack-o-lanterns is Cucurbita pepo. While this species is edible, it is not used for canned pumpkin puree because it tends to be more fibrous or stringy. The primary squash/pumpkin used for pumpkin puree is a variety of Cucurbita moschata called ‘Dickinson’. This variety has a more elongated shape than the typical pumpkin and is nearly the same color as the closely related butternut squash.