Whereas amendments and fertilizers can be incorporated into the earth, pre-mixed soils are prepared and ready to use. Healthy soil is the basis for healthy plants and contains a combination of minerals and organic matter: peat, clay, fertilizer, sand, wood fibers and compost. Good soil will sustain the growth of all types of plants and release the nutrients they need. You can also use soil mixes to replenish poor or deficient soils or to fill pots, containers and planters.