Potassium (K) deficiency, also known as ‘potash deficiency’, is a plant disorder that is most common on light, sandy soils, as well as chalky or peaty soils with a low clay content. Also found on heavy clays with a poor structure.
Most commonly affected fruit and vegetables include potatoes, tomatoes, apples, currants and gooseberries, and typical symptoms are brown scorching and curling of leaf tips, and yellowing of leaf veins. Purple spots may appear on the leaf undersides. Poor flowering and fruit set, often small woody and sweet.
Plants may be more prone to frost damage and disease, and can be confused with wind scorch or drought.
Prevention and cure can be achieved in the shorter term by feeding with home-made comfrey liquid, adding seaweed meal, composted bracken or other organic potassium rich fertilisers. In the longer term the soil structure should be improved by adding plenty of well rotted compost or manure. Wood ash has high K content, but should be composted first as it is in a highly soluble form.
Other physiological plant disorders include;