Potash deficiency is only a problem on tired soils that are deprived of organic matter or remain unfed for some time. Poor flowering and fruit set result and blotchy ripening of tomatoes.
Margins of leaves turn yellow and eventually turn brown and burnt. Severe cases show as leaf spotting and scorch of foliage.
Treatment and control
General tips: Apply a balanced plant food such as Miracle-Gro All Purpose Soluble Plant Food or Miracle-Gro All Purpose Concentrated Liquid Plant Food over the leaves and around the roots. Feed every two weeks during spring and summer. Next year apply a slow release plant food such as Miracle-Gro All Purpose Continuous Release Plant Food or Osmocote Controlled Release Plant Food to the soil in early spring. Feed tomatoes regularly with Tomorite Liquid Concentrate.