This third major nutrient is often referred to as potash or potassium oxide. It helps in the formation of carbohydrates and is necessary for photosynthesis. It also promotes early growth, improves stem strength and contributes to cold hardiness. It also improves the longevity, colour and flavour of fruit. Deficient plants are usually stunted and have poorly developed root systems. Leaves are usually spotted, curled or mottled and may even appear 'burnt' around the edges.
Most soils contain some potassium but it is bound up in mineral form unavailable to the plants. Thus we need to add organic sources of potassium, such as wood ash, hay, leaves or granite dust.
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