Potassium (K): Importance for Plants, Addressing Nutrient Deficiencies and Proper Fertilisation
Plants affected by potassium deficiency grow slowly and develop stunted leaves and underdeveloped fruit. Learn to recognise the first symptoms and act in time before potassium deficiency affects your harvest.
Potassium is an important nutrient for plants, which they need for water transport, flower development and the formation of strong stems. An adequate supply of potassium increases plants’ resistance to pests and diseases and helps them transpire water and photosynthesise more effectively. Along with nitrogen, phosphorus, calcium, magnesium and sulphur, potassium is classified as a macronutrient, which plants consume in the greatest quantities. Potassium is important for plants at all growth stages.
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Potassium deficiency in plants
Potassium deficiency first appears on the lower leaves, where the tips and edges begin to turn yellow. Later, necrotic spots appear on them or they dry out completely. The leaf veins often remain green, while the petioles and stems turn red. The damage is permanent. Plants affected by potassium deficiency during the vegetative phase will be stunted. Extreme potassium deficiency in the nutrient supply leads to the formation of small, underdeveloped leaves.
- drying edges and tips on the lower leaves
- discolouration spreading from the edges towards the centre
- slower growth and smaller flowers
- leaf veins remain green
Potassium deficiency is most commonly encountered when growing in soil, where it can occur even in well-fertilised substrates. The most common cause is the use of incorrectly selected fertilisers. Many organic fertilisers, such as guano, fish emulsion, alfalfa, blood meal and manure from certain animals, contain very little potassium.
Plants absorb less potassium at low temperatures and also when there is too much calcium or ammonium ions (NH₄⁺) in the substrate. Potassium is also poorly absorbed in “salty” substrates full of sodium.
How to supply plants with potassium
The quickest way to supply plants with potassium is by using water-soluble fertilisers with a high content of potassium salts. Flowering fertilisers and PK boosters contain large quantities of readily available potassium for plants. You can supply plants with potassium using seaweed extracts and wood ash.
Remember that fertiliser should be selected according to your growing style and substrate. Although fertilisers containing mineral salts act quickly, when growing outdoors in open soil (in beds), they can lead to a decrease in important soil microorganisms, and nutrients can leach into groundwater. Although organic fertilisers act more slowly, they keep the soil in good condition over the long term.
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It is important to realise that nutrient deficiencies in plants can have many causes, and addressing them correctly requires a thorough knowledge of the principles of plant nutrition. You can find further advice and guides for outdoor and indoor growers on the Higarden blog.