Potassium has been linked with disease resistance. Deficiency of Potassium will led to weak cell walls, reduced plant vigour and changes in the composition of the cell contents, all of which encourage disease infection.

Poatassium is often deficient in in sand based rootzones as it is subject to leaching. Where soil analysis shows there to be a deficiency of Potassium in the rootzone, use fertilisers containing significant amounts of this element.