Adequate soil moisture is essential for good crop growth. A healthy plant is 75 percent to 90 percent water. The plant needs that much water to carry out vital functions, including photosynthesis, support (rigidity), transpiration, and transportation of nutrients and sugars to various parts of the plant. During the first two weeks of growth, plants are becoming established and must have the proper amount of water to build their root systems. Too little water can stunt or even kill tender seedlings, while excessive moisture can prevent roots from moving out into the soil searching for water and nutrients. Without a sufficient root system, hot, dry weather can adversely affect vegetable plants as they mature. In areas prone to repeated drought, select drought-resistant varieties when buying seed or plants.

A table of plant diseases.