Book 29, Question 117
What are the white specks in potting mix?
The white specks are perlite, a volcanic glass that is heated until it pops like popcorn.
It's light and full of tiny air holes, so it keeps soil fluffy and helps water drain. Another ingredient you may see is vermiculite, a mineral that puffs up and holds water. Both are safe, but their dust isn't good to breathe, so wet the mix before using it.