Whether you grew your onions from sets or seeds, by early August the time will come to begin harvesting your onion crops. Onions are bulbous plants and therefore should be treated in the same way as you would treat flowering bulb plants. That is to wait for the foliage or stalks to begin to turn yellow before lifting.
That’s not to say you can’t harvest your onions earlier. Really onions can be harvested at any point from mid June onwards but the longer in August you wait the better formed and larger your onions will be.
The best time to harvest is when onions have stopped growing. The majority of their stalks will have turned yellow and fallen over. This is the point when the energy from the stalks have gone back into it bulb. The bulb will swell beneath the ground given you a larger yield.
At this point, which is generally early august I will start to harvest the first row in my patch. I do so by gently lifting the onion bulbs using a garden fork. By pushing the fork under the bulb and levering back slightly the bulb rises and this in-turn snaps the roots. Once the roots have snapped all growth will stop and the energy from the stalks moves down into the bulb.
One week after lifting the bulbs you can actually harvest them. This really should be done on a sunny day as the bulbs will dry quicker and hence store for much longer.
To lift your bulbs you can do so with a garden fork or just by pulling them by hand. Pull your bulbs and leave them lying out in the sun. Once the onion’s roots have dried (which can take up to 2 days) you then can bring them indoors to store and dry further. You will know when the bulbs are ready to be brought indoors by their roots. If their roots have dried and fall off easily then they are ready for curing indoors. You don’t want to leave your onions outside above ground for more than 2 days or else you can attract pests
To cure, remove the top half of the onions stalks, its best to remove any of the remaining green stalk as these parts are more susceptible to fungal attacks. When remove the stalk be sure to leave 3 inches above the bulb. Choose a warm, dry location that is shaded from the sun but well ventilated to cure your bulbs. Spread your bulbs out so they are not overlapping -onions can take up a lot of space when being cured as they need space and air to dry. After 3 or 4 weeks your onions can be stored. You will know they are ready once the skin layers become loose and start to peel