Hibiscus

Question

My blue bird hibiscus are purple. Is the pH in the soil off and, if so, how can I change this?

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Answer 1

It is not uncommon for the flowers to change appearance, the plant can age and even the sun can fade the flowers.
There are some varieties of blue Rose Of Sharon that are more true to the blue color.
Good care and growing conditions will optimize flowering but the Rose of Sharon flowers are not changed by ph.

https://www.gardeningknowhow.com/ornamental/shrubs/rose-of-sharon/blue-hibiscus-information.htm