citrus peels: Although citrus can be too acidic for some soils, if you have alkaline soil and plenty of oranges, you can start your seeds in orange, lemon, lime or grapefruit halves, as with these orange peel seed starters from My Roman Apartment. When the seedlings are ready to transplant outdoors, snip the bottom of the citrus peel open to give the roots room to expand, and bury the peel below the surface of your garden to allow the peel to slowly compost, not mold.
pumpkin shells: Look how cute these pumpkin seeds started in pumpkin shells are! Although you could start any seed in any pumpkin shell, the easiest method is to start from an actual heirloom pumpkin; simply open it up, insert soil and fertilizer, and then transplant the whole darn thing into your garden. If you’ve ever had volunteer pumpkins grow up in the sneaky spot in your yard where you surreptitiously ditched last year’s Jack-o-lantern guts, then you’ll know how happy pumpkins are to grow this way.
avocado peels: Avocado peel seedling pots are even easier to create than citrus peel seedling pots, since you probably prepare avocados by slicing them in half. Instant seed pot!
coconut shells: The good news about planting something in a coconut shell is that you NEVER have to transplant it! With a hole for drainage, a coconut shell hanging planter is good for years of tropical atmosphere.