Zucchini's Close Relatives

• Other summer squashes have the same cooking time, the same soft texture of zucchini and the same thin skins that only need scrubbing under running water and chopping to be ready to add to the soup in the same proportions as zucchini. Crookneck squash has yellow skin and the flesh has a similar mild flavor as zucchini, while pattypan, a round and flat summer squash, has pale green skin.

Winter Squashes

• Acorn, butternut, delicata and other winter squashes can substitute for zucchini, but in smaller quantities since their flesh is more dense and their flavors more pronounced. Use half the amount of winter squash as you would zucchini. These squashes add bright yellow and orange colors to minestrone as well as sweet flavors. Balance the sweetness in winter squash by giving each bowlful of soup a spoonful of salty Parmesan cheese or basil and garlic pesto sauce, a traditional accompaniment to minestrone.

Green Beans

• While zucchini is a soft vegetable and green beans are harder, they make a good substitute for zucchini because they add green color and an earthy, vegetable flavor. Fresh is always best, but frozen green beans are among some of the better-quality frozen vegetables and will work well. Add green beans to the soup earlier than you would zucchini since they take a few minutes longer to cook.

Dark Leafy Greens

• Chopped kale, collards or spinach, frozen or fresh, add a dark contrast to the red minestrone and easily replace zucchini as one of the soup's vegetables. Like zucchini, leafy green vegetables provide a soft vegetable that contrasts with harder carrots and celery. Add these vegetables at the same time you would have added zucchini, giving them about 10 minutes to cook so their dark colors don't fade.