After evaluating several common seed coating powder materials (i.e. limestone, talc, bentonite clay and montmorillonite clay), we generally felt diatomaceous earth formed agglomerates most consistently.
Diatomaceous earth is composed of fossilized diatom remains that have sharp and jagged microscopic edges. The structure of the diatomaceous earth may aid in the formation of agglomerates by decreasing the flowability of the coated seed and promoting seed clumping.