It is especially needed for lawns and leafy crops. Since it produces a very noticeable affect on plant growth there is a tendency to overuse it. A deficiency is usually pH related. Unlike phosphorus, potassium leaches out fairly readily and may be wasted if a heavy rainfall occurs right after a fertilizer application. On the other hand, heavy applications provide no benefits to plants and may actually injure or burn them.
Potassium tends to magnify the benefits of nitrogen and phosphorus.
In addition, it stimulates vigorous growth, disease resistance and a resistance to cold temperature. Plants with a potassium deficiency have weak stems and leaves that appear dry or scorched with irregular lesions on the surface. Occasional addition of fertilizers containing micronutrients may be necessary in sandy soils, areas of high precipitation and in soiless mixes. Micronutrients are also listed on the package. Inorganic forms are generally more immediately available to the plant but are also more subject to leaching.