The onions should be grown after 60-80 days. They will, however, go rotten if you leave them ripe for too long. You will know an onion is ready when:  The onion bulb fully emerges from the soil.   The green sprouts wilt and/or turn brown. Flowers stalks appear. When the sprouts have turned to full onion bulbs that look ready for consumption, you can harvest them. Don't be scared of ripping out the roots. Handle them carefully and lay them out in a single layer to avoid bruises.This will begin the curing process and allow excess soil to fall from their skins. You can use a knife or garden scissors. This will stop the onions from decaying in storage. You will know they are cured when the foliage shrivels and the onions produce a papery outer layer. A shed or garage floor works well; anywhere that is cool, shaded and dry. The curing process will normally take around one month.  You can skip the curing process if you wish to eat the onions straight away but storing them without curing first carries a high risk of mildew and rot.  If you can't find anywhere dry enough to cure the onions, consider using a dehumidifier to keep moisture levels down.. This will ensure they remain in the right conditions and do not damage other fruit. The onions are now ready for consumption! You will want to eat the onions within a single month. If an onion sprouts, you can replant it again!
Look for signs that the onions are ready for harvest. Pull the onions from the ground once they have ripened. Place the onions outside on dry ground for a few days. Clip the roots and cut 1 inch (2.5 cm) from the onion's foliage. Keep the onions on cool, dry ground until dry outer skins form. Store the onions in baskets or dry mesh bags.