These all are regrown by placing the roots in a dish of water. Cut the leaves or stalks off to about an inch above the roots. Place the root end in a dish of water. Make sure that the roots are inside of the water, but do not submerge the rest of the plant. Place in a sunny window & spray with water 1-2 times a week to keep the top of the plant moist.
Onions are one of the easiest vegetables to regrow from scraps. Just cut off the root end of your onion, leaving a 1’2 inch of onion on the roots. Place it in a sunny location in your garden and cover the top with soil. Make sure to keep the soil moist by watering when needed. As you use your home-grown regenerated onions, keep replanting the root ends you cut off, and you’ll never have to purchase onions at the store again.
You can re-grow a plant from a single clove. Simply plant it with the root-end down. Sit the plant in a sunny window. Once established, cut back the shoots and the plant will put all it’s forces into producing a nice garlic bulb – full of flavor & capable of repelling sparkly vampires. You can repeat this process with a clove from the new bulb you have just grown.
Source : mrshappyhomemaker