My two rhododendrons did not produce any blooms this year- they are healthy otherwise. Why?
I had the same problem with one of my rhodies this spring (all the others were fine), as did many other people in the Pacific Northwest. Following are the most likely causes:
NO FLOWERS, BUDS DO NOT OPEN. This is most likely to be caused by frost, either in mid-winter by the hardest frosts of the year, or in spring when the buds are swelling and about to open. Certain varieties have very frost-vulnerable swelling buds, while many species have buds which are easily destroyed even by quite mild winter frosts.
NO FLOWERS, NO FLOWER BUDS. There are several possibilities why rhododendrons may not flower freely:
- Too much shade. This is very common in North America where, in order to regulate sun and soil temperature, plants are placed in deep shade. This allows healthy, if straggly growth, but can inhibit flowering. The more light you can give a plant, the more likely it is to flower, so there is a trade-off between the need for shade and the need for light.
- The variety takes many years to flower (it does not sound like this is your situation).
- Kindness. Rhododendrons flower in order to reproduce. A contented, well-fed, well-watered well-shaded plant may not feel any need to reproduce, as it perceives no threat to its survival. Do not feed after mid-summer, as this encourages growth at the expense of flowers. Nurserymen cut down watering in late summer to stress plants into flowering the following year.
(Source: Rhododendrons: A Care Manual, by K. Cox, 1998, p. 73).
The above is corroborated in other sources, e.g. Success with Rhododendrons and Azaleas, by H.E. Reiley, 1992, p. 132-133.