Amending Clay Soil: What Counts as Organic Matter?

Defining Organic Matter for Clay Soil Improvement

A follow-up question asks for clarification on "organic matter" for clay amendment, noting it's not gypsum or lime.

Answer

Organic matter means compost, humus, and aged manure. These materials feed soil life—earthworms, bacteria, fungi, nematodes—which naturally incorporate them into clay, improving tilth, aeration, and nutrient availability. Gypsum and lime correct soil chemistry (pH, structure) but don't feed soil biology. Think of organic matter as groceries for soil organisms; they "cook" it into plant-available nutrients.