Healthy levels of potassium in the soil has many benefits, including aiding protein synthesis, stimulating root growth and neutralizing acids. A bit too much potassium in garden soil is not typically a problem for most plants, but in high excess, potassium can cause problems. One major problem is the inhibition of calcium. Common causes of exorbitant potassium levels include over-fertilizing and a large number of rocks and minerals in the soil. Correct a potassium problem by draining and filtering the soil or by switching fertilizer types.
Loosen the soil deeply with a shovel, and water thoroughly to dissolve water-soluble potassium. Allow the soil to fully dry, and repeat digging and watering the soil two or three more times.
Sift through the soil, and remove as many rocks as possible, using a soil sifter. Minerals occurring in rocks such as mica and feldspar slowly release potassium into the soil slowly through weathering.
Stop applying potassium-rich commercial fertilizer. Apply only commercial fertilizer that has a '0' in the final number field. Commercial fertilizers use a three number system for measuring levels of nitrogen, phosphorous and potassium. The last number stands for potassium. Another option is to stop using commercial fertilizers all together and to begin using only organic matter to enrich the soil.
Mix crushed eggshells, crushed seashells, wood ash or soft rock phosphate to the soil to add calcium. Mix in up to 10 percent of organic compost to help amend and balance the soil.