Wild onion, also known as wild garlic, is found in lawns, fields and even randomly growing in gardens. The plant, a close relative to the typical onions grown from bulbs and seeds, has a slightly similar yet distinctly milder taste when compared to other onions. The smell is a combination of both onion and garlic, making it very discernible.
Verify that the wild onions you have found are in fact wild onions. Pull the plant out of the ground. Tug gently and wiggle the base of the plant to ensure the bulb comes out with the plant. Know that the bulbs will be much smaller than traditional onions, even spring onions.
Smell the bulbs. You will notice a distinct scent of light onion and garlic. If you do not detect the smell right away, use your fingernails to scrape some of the surface skin off of a bulb and smell the plant again. If in doubt, discard the plant and find another with a stronger, more recognizable smell.
Trim the greens and roots off of the plant. Use only the bulb for eating. Peel back the outer layer of the onion and use thinly sliced on salads, added whole or chopped to soups and stews or even saute in olive oil to add to dishes calling for onions or garlic.
Take notes regarding where you have found patches of wild onions to know where to find them again.
Use caution before eating any plant until you have made certain the plant is edible. Many plants that look like wild onions are poisonous.