Eventually the world is supposed to explode and destroy us all. Before that, however, it's supposed to turn into an apocalypse with mass starvation. So...to prepare for the worst--or to simply save money--you can grow vegetables from mere scraps! Here's how:
Find a potato with significant amount of eyes. You may need two potatoes. Cut the potato into 2-inch pieces with a couple eyes per piece. Leave to dry out completely for a couple days. With eyes facing upward, plant in a hole that is about eight inches deep. Cover with four inches of soil. As the sprouts poke through, cover with more soil.
Leeks, Onions, Fennel
You know that white part at the end of leeks and green onions with the tiny root threads? That's the part of the plant that needs to be submerged in a glass jar of water. You don't need much water, just a little. As they grow, you can snip what you need, leaving the white part and roots behind in the water. It will spring forth as long as it's in the jar. Keep in a sunny spot and change the water weekly.
All you need to start this is a single garlic clove. In plenty of direct sunlight, plant the clove, root end down, in soil. Before long, it will produce new shoots. Once it's established, you'll want to cut the shoots with the exception of one. This will turn into a single large bulb ready in no time.
The more difficult to regrow, it's not impossible to get mushrooms to crop up in the right conditions. In a portable tray, plant the stalks of mushrooms (exposed, with caps removed) in a mix of soil and compost. Warm filtered light during the day and a cool temperature at night is the best condition for the fungus to thrive. Wait a couple days and see what happens. Either the mushrooms have taken to the soil and temperature or they've rotted. Obviously, if they're rotted, you need to dispose of them.
Never buy onions again. Simply chop the bottom root portion from an onion--leaving about half an inch of onion intact. Plant root facing down in soil and keep moist. Temperature should be warm and sunny. As you use onions, simply repeat the process and never buy them again.