Please, please, do not put packing peanuts into your garden's soil! Most packing peanuts are made from polystyrene, which is not biodegradable. They will remain long after you and your garden have passed from this earth. Biodegradable packing peanuts made from plant starch won't help your soil either, because they dissolve when they get wet.
Improve the drainage, tilth, and overall quality of your soil by mixing compost into your garden beds. Even better, double-dig your beds. This process adds organic matter and loosens the soil, making it easier for water and air to reach the roots of your plants. For instructions on double- digging, see "Start a Fresh Bed" in our March 2004 issue. Another option is to build raised beds and fill them with a high-quality, well-draining topsoil.
Whichever method you choose, allow the newly fluffed soil to settle for a couple of days before planting. And don't walk on your new bed; you'll compact it and undo all your hard work.
As for your packing peanuts, recycle them at a local store that provides packaging and shipping services. That's the most sensible way to get these nuts off your hands.