Rose of Sharon Needs "K"

August 2022

Ever since the big Spanish broom was removed in 2021, the Rose of Sharon that had been strangled behind it has done better and better. 

I pruned it way back in the winter of 2022, and it formed a nice shape and bloomed pretty well the following summer. Here it was in August 2022. →

Actually it bloomed okay even hidden behind the broom with little sun. In 2018 it was badly affected with aphids, but since 2019 it has been getting a winter soil drench from Coates and aphids have not been a problem. 

in mid August 2020

← It bloomed pretty fully in 2020 as it reached out from behind the Spanish broom to find some sun.

But now, four years after clearing out the broom, the Rose of Sharon continues to have a nice shape but just isn't blooming much. 

In August it had flowers and buds but they seem scattered oddly and sparsely. Pretty enough, but nowhere near as densely flowered as other Rose of Sharons I see, and not even as flowery as it has been in the past.

What's going on? Same issue with the butterfly bushes this year.

August 16, 2025

I gave it extra water all spring and summer and a couple applications of 2-8-4 fertilizer when I watered. It has irrigation emitters.

But somewhere I read the following:

Many flowering plants prefer plentiful phosphorus -- the middle number in the N-P-K ratio -- but Rose of Sharon and its hibiscus relatives favor potassium (the K) instead. 

Citrus & Avocado fertilizers of 5-3-4 are formulated to provide greater potassium, and hibiscus needs iron and magnesium too.

The leaves are not chlorotic, but inability to take up iron is an issue in my soil. And I guess I needed to use a citrus fertilizer or something with higher potassium?

The individual flowers look nice. A close up shows that. I've inspected for insect damage, but all the buds and flowers look fine.

There just aren't very many of them.