For some people, the first full day of spring means it's time to break out the gardening gear. Believe it or not, gardening is a great form of exercise. Planting new trees, flowers and seeds for an hour can burn 300 calories. But before you get out into the dirt, it's important to stretch and to not overdo it. Also, it's important to lather on the sunblock so you don't get burned by the sun.