Many fertilizers that are sold for greater blooms (numbers and size) usually have high P a lower K and much lower N. And some will have a very high K, a somewhat high P and a low N. While I can understand the low N, I am a little confused about the P and K. Once I was visiting a commercial apple orchard and the owner said that for their mature trees there fertilization is always for higher K values as this leads to greatest bud set. Isnt P mainly for roots and energy and so will definitely contribute to blooms but what role does K play here? What do know/think?

Thanks!