As the foliage is dying down is best. I like to get them while the leaves are yellow and starting to brown, if I wait too long they are sometimes hard to locate. Spread them out and allow them to dry, and remove any attached foliage when it dries and detaches easily, with little or no resistance. Once the bulbs are dry and chaff removed, you can store them in onion bags till replanting in fall. I store them in summer at room temperature, where air circulates well.
