What is Organic Compost? Organic compost is organic matter that has been broken down by microbes. Compost is a key ingredient in all soils. It adds organic matter, improves sandy soils, encourages beneficial microbes and earthworms, increases nutrients, and improves soil texture. Compost is the ultimate ingredient for building fertile soil. If everyone composted their kitchen and garden waste, the world would be a cleaner place, and we would all enjoy more productive organic gardens. ood compost has a wide array of beneficial ingredients that can give new life to your garden or farm. While the bulk of all compost is organic material, some composts are better than others.