In the climates where butternut squash is most often grown, the squash grow during the warm summer months and are harvested in early autumn before the first frost. Butternut squash are ready to be harvested when they have reached full size and their skins have turned from green to tan. Ensuring that the skins are mature before harvesting butternut squash is very important because the hard rind allows for lengthy storage. When the squash are ready to be harvested they should be trimmed from the vine, cleaned, and stored in a cool, dry place.
Despite being called a “winter squash,” butternut squash do not grow in cool temperatures. The plants grow and the fruits develop during warm summer months, and the squash must be picked before the cooler weather sets in and brings frost. All it takes is one frost to kill the plants and destroy their yield, so harvesting butternut squash in a timely manner is essential.
Butternut squash have soft, green-striped skins while they are growing and still immature. Harvesting butternut squash while the skins are still soft and green will result in hard, flavorless flesh because the fruits are still underdeveloped. Instead, butternut squash should be harvested when the skins have completely turned from shiny green to a matte, medium tan color. Additionally, the skins should be hard and resistant to scratching from a fingernail before they are harvested. Stems should be thick and hard, and indicate readiness for harvesting when they begin darkening from green to brown.
Mature butternut squash that are ready for harvest should be carefully trimmed from the vine, leaving 1–2 inches (2.5–5 cm) of stem attached to the squash. Failing to leave some stem attached will result in a soft spot on the fruit that can invite insects or bacteria that cause premature decay. While harvesting butternut squash, any fruits with cuts, soft spots, bruises, or missing stems should be set aside. These specimens are still edible but should be eaten first because they are likely to rot quickly and not store well. Rotting squash that is stored among healthy squash can expedite spoiling the whole harvest.
After harvesting butternut squash, healthy, mature fruits can be stored in a cool, dry place for several months. Basements or root cellars are often good choices as long as they are not prone to dampness or humidity in the winter months. Temperatures of approximately 50–55 degrees Fahrenheit (about 10–13 degrees Celsius) are ideal for storing butternut squash.