Cut the last inch off of each onion (this will give you the bulb and roots). Plant these in a flower pot or in your garden. Be sure to cover the bulbs completely, and to leave a portion of each stem sticking out above the soil. Water regularly, and watch your green onions grow back. To harvest, simply cut off as much of the green stalks as you need. If you leave the white bulbs in the plant, they'll continue to regrow more greens. Expect to get three to four cuttings off of your green onions before you need to plant more.
Cut the bottom inch off of a bunch of celery. Place the celery piece in a bowl, cut side facing up; and add a bit of water (just enough to submerge the bottom of the celery). Move the bowl to a sunny spot, and wait for leaves and roots to form (this should only take a few days). Then, plant the celery in your garden, covering everything but the leaves. Wait for the celery stalks to grow back. Then, cut off as much as you need. As long as you leave the root in the ground, your celery will grow back again and again.
Soak your ginger overnight. Then, cut it up into pieces. Make sure you have a couple growth buds on each piece (they're the little bumps on the end of each finger). Plant your ginger with the growth buds pointing up or to the side (you just don't want them facing down). Then, water regularly. Ginger likes to have moist, but not soggy soil at all times. To harvest, simply dig up one of your rhizomes (pieces), and cut off what you need.
Leaf Lettuce and Greens
Any time you harvest leaf lettuce from your garden, pick the outer leaves, but leave the inner leaves untouched. As long as the crown of the plant remains undamaged, your lettuce will continue to produce new leaves all season long.
Cut a one-inch (approx.) chunk from a potato that includes one or two eyes. Give the piece a day or two to dry out and skin over. Then, plant with the eye (or eyes) facing up.
Bury all or part of a sweet potato under a thin layer of soil. Wait for slips to grow from the sweet potato and reach at least four inches in height. Pull the slips off, and plant them.