Potash: identify a deficiency so you can correct it. Necrotic or deformed leaves, flabby stems, delayed growth...
A certain number of symptoms are indicative of a lack of potash. Potash refers, in reality, to various compounds or salts containing potassium (potassium oxide, potassium carbonate, potassium chloride, etc.) of chemical or natural origin. Adding potash to soil is not trivial and can have undesirable effects. It is preferable to turn to fertilizers which naturally combine potassium and magnesium.