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Plant Answer Line Question

Keywords: Rhododendrons--Washington, Rhododendron

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.

Date 2018-03-01
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Plant Answer Line Question

Keywords: Washington Park Arboretum, Rhododendrons--Washington

Would you be so kind as to tell me when rhododendrons are usually at their peak bloom?


The peak season for Rhododendron blooms would probably be May, but there are Rhododendrons which bloom earlier and later than this as well (March through June). For more detail about which species bloom at what time, you may find this link to Oregon State University's Landscape Plants web site of interest.

From the Washington Park Arboretum's list of plants at their peak:

March: Camellia, flowering cherry, corylopsis, daphne, forsythia, heather, hellebore, magnolia, rhododendron, witch hazel.

April: Azalea, barberry, camellia, flowering cherry, halesia, maple, madrona, magnolia, rhododendron, serviceberry.

May: Crab apple, dogwood, magnolia, mountain ash, rhododendron, red bud, serviceberry.

June: Rock roses, brooms, Korean dogwood, rhododendron, stewartia, styrax

Date 2017-07-18
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May 31 2018 13:14:08