Most stabilized composts have a pH of about 7.0. Information on the amounts of metals such as zinc, iron, lead, nickel, and cadmium in the compost should also be studied. Metals content should be well below the threshold values shown in Table 1. As a soil amendment, compost is thought to enhance the physical, chemical, and biological properties of soils. In clay soils, organic materials such as compost and pine bark increase drainage and air space.
Compost tends to raise pH and increase biological activity in the soil.
In sandy soils, compost increases the ability to hold moisture and nutrients. Landscapers find that all of these characteristics help ornamental plants become established and develop a good root system. Table 2 gives suggested application rates. This amount is approximately equal to 880 to 1,300 pounds per thousand square feet. Yard waste compost can be applied at a higher rate because it contains fewer nutrients.