Soil is made up of different-sized inorganic particles. Some soil is extreme in its makeup by having a high sand or clay content. Both sand and clay have problems when growing plants. The best medium to grow plants in is potting soil.
Potting soil is made up of equal parts of silt, clay and sand. The silt is full of nutrients for the plants. Potting soil drains quickly, while holding onto just enough moisture to encourage plant growth. Potting soil also allows plenty of oxygen to reach the roots.
Soil made up mostly of sand presents plants with certain growing issues. Sand does not hold moisture like normal soil or clay, so plant roots stay dry. Sand tends to have limited fertility. Add topsoil and organic materials like rotted leaves and peat moss to fix these problems.
Soil with a high amount of clay tends to stay very wet when watered. The prolonged wetness makes it difficult for plant roots to have an adequate supply of oxygen. Clay soil is subject to compaction, which creates a hard, cement-like soil. Each year, plenty of organic material is needed to fix the drainage and compaction problems.