When you're gardening in heavy clay soil, sandy soil, or you want to lower the pH of your soil, you need to work in Back to Nature Cotton Burr Compost. This soil amendment contains sulfur - the powerhouse micro-nutrient that helps lower soil pH. Properly composted cotton burrs are also an excellent food source for the beneficial soil organisms that help to make nutrients available to plants and help to keep harmful organisms and diseases in check. 2 cu. ft. bag.