Healthy, moisture retentive, well drained soil is one of the single most important elements of successful, organic gardening. Creating healthy soil in sandy or heavy clay soil is as easy as adding composted manure or worm castings. This increases moisture retention and improves the soil structure and fertility which encourages millions of micro-organisms to thrive. Their existence increases the absorption of essential minerals to the plants which creates better root growth and greater resistance to disease and pests.