This is the third entry for the Understanding Soil Nutrients Series. Today we will focus our attention on a very important soil nutrient - potassium. If you missed the first and second entries to this series, here they are:

Understanding Soil Nutrients - Nitrogen

Understanding Soil Nutrients - Phosphorus

Why Potassium is Important To Your Vegetable Garden

Potassium (K) is generally called potash when used in forms for a soil fertilizer. The name comes from the collection of wood ash in metal pots when the soil benefits of this material were first recognized centuries ago. Hence, the name "potash" came to be.

This nutrient is essential for vigorous growth, disease resistance, fruit and vegetable flavor and development, and general plant function. Potassium breaks down slowly so you won't have to add it very often. Deficiency symptoms include yellow areas along the leaf veins and leaf edges, crinkled and rolled-up leaves, and dead twigs. Fruit trees may develop fruit with poor flavor or stunted fruits. Certain animal manures and mineral fertilizers, such as greensand, add potassium to the soil.

There are several different forms of potassium available for use in your vegetable garden, here are a few:
    • Muriate of Potash - Muriate of potash is potassium chloride containing between 50 to 60% potash. Its chlorine content passes off rapidly when applied to soil, and is harmful to certain beneficial bacteria. Some authorities think sulfate of potash makes a better potash fertilizer.
    • Sulfate of Potash - Sulfate of Potash contains 48% potash. It is more expensive than muriate of potash but is considered less harmful to bacteria and plant roots. It also does not contain the chlorine that is in muriate of potash.
    • Wood Ashes - Organic gardeners rapidly accept wood ashes, since it is truly organic in nature. Wood ashes contain about 6% potash, plus good amounts of lime. At one time used corn cobs were put in piles and burn. The ash remnants of the burnt cobs contained up to 35% potash. Almost any ash resulting from burning organic materials that contain some fiber should be a decent source of potash fertilizer. Wood ashes are particularly good to use for adding potash to compost.
When using a fertilizer, check the N-P-K rating on the back of the container. These numbers represent the percentage of each macro-nutrient in the fertilizer. Potassium (or K) is usually the last number in the N-P-K rating. In the picture below, this fertilizer has 2% nitrogen, 1% phosphorus, and 1% potassium.

The Last Number Represents The Percentage of Potassium

Make sure to complete a thorough soil test on your vegetable garden soil before adding potash. If a potash deficiency is detected, potash can be worked into the garden soil usually once a year, when the soil is being readied for planting.