Fruits and vegetables grow best in moist, well-drained soil. Hold a handful of garden soil to test its condition. It should be dark brown or black and fall in crumbles from your hand. If the soil stays in a ball or flows like sand, it needs organic matter added. Compost is organic matter. It is the organic matter that helps retain moisture for plants to use when they need it.
The Nobel Foundation report on organic matter in soil describes organic matter content as essential for its water-holding capacity. According to the foundation, "Organic matter behaves somewhat like a sponge, with the ability to absorb and hold up to 90 percent of its weight in water." Water absorbed into organic matter is then made available to plant roots as needed. It is a self-regulating system of water-on-demand.
Soils are 45 percent minerals, 25 percent each air and water and 2 to 5 percent organic matter. Organic matter is plant and animal materials that have decomposed and become humus. Soil texture is determined by the mineral composition and is most often described as clay, sandy or balanced. Well-draining soil is neither too sandy nor clay-like. Sandy soil does not absorb water, and clay soil allows it to pool on the surface.
Adding organic matter to garden soil improves its moisture-retaining capacity. Backyard composting is the easiest way to provide organic matter content for garden soil. Compost is created from natural materials such as leaves, kitchen scraps, newspaper and yard clippings. They are put into a compost bin in layers and watered regularly. The materials decompose and create organic matter within two to four months.
Plant roots need moist, well-drained soil to grow well. They absorb water and nutrition from soil. Healthy soil retains water and supplies nutrition through the roots. They spread easily in soil that is neither soggy nor excessively dry. Roots are held in place on soil aggregates created from organic matter and minerals. Compost is rich in mineral and organic matter content.
The creation of moist, well-drained soil is a process that takes time. Compost added regularly as a fertilizer and soil amendment improves the soil and increases nutritional value of food grown on it. No-till gardening methods also improve soil conditions by allowing plants to decompose naturally and reducing disruption of the soil microorganism populations.