The plant gets buds, but they either fall off or else open up into few poorly-blooming flowers that are not at all spectacular. I've fertilized. I've had them in both shade and sun. I've watered them... what else do I do? Another question is about our Ash tree. It bloomed but has very few berries. Doesn't make sense to me. Flowers should bear berries, no?
Why Doesn’t My Impatiens Bloom?
Certified GKH Gardening Expert
You may have over fertilized. To much Nitrogen can cause lack of flowers.
You can add phosphorous. Bone Meal is a good treatment.
Your lack of berries on your Ash Tree may be nothing more than environmental changes. Some years it may have abundant flowers and berries, some years less.
Here are links with more information.