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When you notice the leaves on the first few plants start to fall over, stop watering and leave the onions in the ground for 7 to 14 days (depending on how dry or humid your climate is) to allow them to finish maturing.
The same holds true for rain—if most of your onions are fully grown, harvest them all before a big rainstorm is expected because moisture spells trouble for mature onions.
On a dry, sunny day, carefully pull each onion out by the bulb, or dig around the plant to lift the bulb from the soil.
After a nice day of getting some sun, move the onions into a sheltered, shady spot (under a tree, on a covered porch, or in a well-ventilated garage, for example) and spread them out one by one.
You don’t need to clean off the onions yet. Just set them out to dry, dirt and all, until the stems turn brown and brittle. This rest period allows the onions to go deeper into dormancy so that they’re less susceptible to disease.
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