What Does Potassium Do for Plants?

Potassium is an essential element for plant growth. It is commonly applied to gardens, lawns and orchards as part of a regular fertilizer program. Garden potassium, usually in the form of potash, helps plants use water and resist drought as it regulates overall plant growth and health. Potassium is especially important to edible crops and enhances the size and quality of fruits and vegetables.

When plants do not have enough potassium, they have symptoms such as stunted growth, poor flower development and lower quality fruit or vegetable harvests. Plant leaves may look scorched and curl at the tips. As potassium-deficient plants grow, the leaves curl along the edges and often appear dry, white-spotted or crinkled at the edges. Growth is slow, and wind or high temperatures easily damage the plants.

Potassium is a common mineral in soil, but often only a fraction of this potassium is available for plants. Some forms of potassium are easily absorbed for plant growth. Other potassium forms are not usable by plants. Gardeners and agriculturists discovered that if potassium in the soil is not in a plant-friendly form or if the soil is potassium-depleted, other kinds of potassium can be applied as fertilizer for healthy plants.

Potassium is commonly applied in solid or liquid fertilizers. Commercial fertilizers list the three major plant nutrients in label percentages, such as 5-10-5, known as the NPK ratio. The first number is Nitrogen (N), the second is Phosphorous (P) and the third is Potassium (K). Solid, granular fertilizers are scattered around garden plants or spread on lawns and watered in. Liquid fertilizers are applied through spraying or watering. In greenhouses, potassium is sometimes applied through irrigation systems.

Potassium in commercial fertilizers is water soluble, meaning it readily dissolves in water and can be absorbed by the plant roots. Potassium controls plant stomata, the cells that control water. Without enough potassium, the stomata do not efficiently use water and the plant becomes becomes vulnerable to disease and heat stress. Potassium also aids the enzymes promoting plant life. Without potassium, the plant cannot cycle the nutrients to feed roots, leaves and fruits.

Potassium grows healthy lawns by promoting green sturdy plants on deep roots. It aids roses (Rosa spp.), hardy in U.S. Department of Agriculture plant hardiness zones 4 through 11, and other flowering plants by encouraging strong stems and well-developed flowers. Farmers depend on potassium for healthy crop production. Plants rich in carbohydrates such as potatoes (Solanum tuberosum) need potassium for tuber growth. Potassium regulates plant growth so that harvested fruit is fully formed, high quality and has a better shelf life for consumers.