 Most winter squash is harvested in September or October in the Northern Hemisphere, before the danger of heavy frosts.Winter squash is a low-calorie food and a good source of complex vegetable carbohydrates and dietary fiber.It is an excellent source of vitamin A, a great source of vitamin C, potassium, dietary fiber and manganese, and a good source of folate, omega-3 fatty acids, vitamin B1 (thiamin), copper, tryptophan, vitamin B6 (pyridoxine), vitamin B3 (niacin) and vitamin B5 (pantothenic acid).