We harvested potatoes from a flower bed in July and had a successful crop. The potatoes could have remained in the ground a bit longer but the tops died back and the plants no longer looked attractive.
I had onion sets in the refrigerator from spring and I planted them the second week of July. After planting, I covered the bed with wire to keep the cats out. The onions are now growing through the wire. Maintenance will be easy as there are few weeds. We will thin by picking the occasional onion for salads and should have large onions by fall.