Vermiculite is a mineral that flakes easily and expands in high temperatures. It is commonly used in potting mix, and can resemble small pieces of Styrofoam, such as the kind used to make most types of packing peanuts. Vermiculite, however, is not interchangeable with packing peanuts in potting mix. Vermiculite is heated to high temperatures to form a lightweight aggregate that gives the soil room for air in the potting mix.
Attributes of Vermiculite for Potting Mix
Though the vermiculite expands greatly to form an aggregate before it is used in potting soil, it can be squashed if handled too aggressively. This decreases the amount of air that gets to the roots of the plant. Another difference between Styrofoam and vermiculite is that the vermiculite actually holds fertilizer and water, giving the roots of the plants more access to nutrients and moisture.
Attributes of Packing Peanuts
There are a few different kinds of packing peanuts. The kind that is best known is made from Styrofoam, but environmental concerns about the non-biodegradable nature of this material have led to a slew of other kinds of packing peanuts. One very common substitute for the basic Styrofoam packing peanut is a starch-based packing peanut. These are water soluble and can even be composted. Since these packing peanuts dissolve in water, however, they are not a good substitute for vermiculite in potting mix as they do not continue to aerate the soil when they are moistened.
Potting Use for Styrofoam Packing Peanuts
There is some use, however, that you can get from your Styrofoam packing peanuts when potting plants At the bottom of the pot, put in a layer of packing peanuts before you add the potting soil and the plant. This aids in water drainage for the plant.