Answer: The answer depends upon the types of onions you are growing. For instance, small bulbing onions can go into a 1 gallon pot (8-10 inches deep). Large onions, like Walla Walla's, will need about 12 inches of root and bulb space so a 3 gallon pot will work. Just figure approximately how large the onion bulb will be and add about 6 inches below and one inch above to accommodate the roots, the mature bulb, and an inch of stem before top growth begins. Hope this clarifies things for you!
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