There are many different foods that can be regrown using their scraps. Using food scraps to grow newfoods can be a fun way to both save money on your grocery bill and reduce food waste.
Plant even just a single clove root-end down and you will see results. Plant in shallow ground in the sunniest part of your garden.
When your recipe only calls for the green part, don't toss the white end with the roots. Drop them in a glass with enough water to cover them, and move the onions around so the roots are pointing down. Make sure you change the water out once every couple of days so they don't get greasy. Within about a week you'll have a brand new set of green onions.
Just take the base of your leeks and cute straight across the bottom. Cover them in water, and leave them in the window with some sun for a few days. You should start seeing them sprout right away, and within a week or so you'll be able to trim off parts to use in recipes.
Take the leftover fennel roots and place them in a small container filled with water. Keep on a sunny windowsill just as you did the leeks. You can plant in the ground if you'd like, but you don't need to for success. Just make sure that you change the water every week.
Similar to leeks, romaine lettuce will re-grow from the white root end. Cut the stalks off as you normally would, and place the root end in a shallow bowl of water enough to cover the roots but not the top of your cutting. Place it in a sunny window position. After a few days, you should start to see roots and new leaves appear. After a week or so, transplant it into soil with just the leaves showing above the level of the soil. The plant will continue to grow, and within a few weeks it will sprout a whole new head.
Take the roots of the lemongrass that you don't use in your cooking and put them in a container full over water. Place the container on a sunny windowsill. Once you can spot new growth then place the plant into a pot with soil and return it to the windowsill. Wait until the roots are about a foot tall and then cut off what you need for cooking. The roots will continue to sprout, as long as you keep it healthy.
When chopping the celery leave the base of the plant intact. Put the base in water and leave it for about a week, changing the water every couple of days. Once you notice yellow leaves growing out of the stem and the outer stalk starts to deteriorate, this is when you can plant it into a pot with soil. The temperature needs to be warm, but not too hot!
Plant your ginger scraps with the newest buds facing up in a pot of moist soil. Because ginger is a tropical plant it prefers humid conditions. You will notice green shoots come out of the soil and spread out. After about four months it should be reading for harvesting.
Once potatoes start to form 'eyes' on them, Cut the potatoes into 2 inch pieces, while making sure each piece has 1-2 'eyes' on it. leave the pieces in room temperature for a few days; this allows the cut surface area to dry out so they don't rot in the ground. Plant the pieces in a pot filled with rich, moist soil. Plant them 8 inches in depth with they 'eyes' facing the sky.