We do not recommend canning summer squash or zucchini. We recommend preserving summer squash or zucchini by pickling or freezing.
USDA has withdrawn recommendations for canning summer squash, including zucchini, that appeared in former editions of So Easy to Preserve or USDA bulletins. The reason for withdrawal is uncertainty about the determination of adequate processing times. Squash are low-acid vegetables; they require pressure canning for a known period of time to destroy the bacteria that cause botulism. Documentation for the previous processing times cannot be found, and available reports do not support the old process. Attempts to reproduce the old process did not result in adequate heating to ensure safety. Slices or cubes of cooked summer squash will get quite soft and pack tightly into the jars. The amount of squash filled into a jar will affect the heating pattern in that jar and may result in inadequate processing and an unsafe product. (References: http://nchfp.uga.edu/questions/FAQ_canning.html; http://www.clemson.edu/extension/hgic/hot_topics/2007/08summersquash.html)
Summer squash is good for you. It is low in calories and many varieties provide vitamin C, potassium and, if the skin is eaten, beta carotene. Preserve summer squash by freezing, pickle them for canning or dry them.
Freezing Summer Squash: Choose young squash with tender skins. Wash and cut in ½-inch slices. Blanch in boiling water for 3 minutes; cool in ice water for at least 3 minutes. Drain and package into freezer bags or freezer containers, leaving ½-inch headspace.
Pickling Summer Squash: Squash Pickles-I
(Yield: 2 pint jars) This sweet squash pickle recipe is from So Easy to Preserve, p. 145.
2 pounds fresh, firm zucchini or yellow summer squash
2 small onions
¼ cup salt
2 cups white sugar
1 teaspoon celery salt
1 teaspoon turmeric
2 teaspoons mustard seed
3 cups cider vinegar
Wash squash and cut in thin slices. Peel and slice onions thinly. Place onions and squash/zucchini in a large bowl and sprinkle with salt. Cover with cold water and stir to blend in salt. Let stand 2 hours. Drain thoroughly. Bring remaining ingredients to a boil. Pour over squash and onions. Let stand 2 hours. Bring all ingredients to a boil and heat 5 minutes.
Pack vegetables into hot jars. Leave ½ inch headspace. Fill jars to ½ inch from top with boiling liquid. Remove air bubbles. Wipe jar rims. Adjust lids. Process 15 minutes in boiling water bath canner.
Note: See So Easy to Preserve (p. 145) for recipe for squash dill pickles.
E.L. Andress and J.A. Harrison. 2006. So Easy To Preserve. Georgia Cooperative Extension/The University of Georgia. “Pickled products” Pp. 117-186.