As hobbies go, gardening is pretty eco-friendly, but the little trick of starting seeds in eggshells is even more impressively so. Once you're done, plants go into the soil, egg box goes into the recycling and eggshells go for compost. Chances are, you won't have to buy anything special to get started, either!
This technique is ideal if you only have a little space to work with, because it'll tuck neatly onto your windowsill. Pop over to gardening blog Garden Betty to find out exactly how it's done, plus tricks and tips on what to grow.