Plant lovers are aware of the vibrant, showy flowers Rhododendron exhibit in spring. But did you know that some rhododendrons can display subtle yet colorful foliage that is worth taking notice of in the fall? When you visit Holden Forests & Gardens this time of year, take a stroll through the Layer Garden and look closely at the Rhododendron in our collections. The genus Rhododendron consists of elepidotes, lepidotes, evergreen azalea, and deciduous azalea. Lepidote rhododendrons and many azaleas are displaying beautiful colors including shades of gold, scarlet and burgundy. The Medeiros Lab has been observing these color changes and will take a closer look at leaf pigments to work towards finding answers regarding why these leaves change the way they do.

Many rhododendrons are evergreen, keeping green leaves throughout the winter. However, azaleas include a mix of evergreen azaleas and deciduous azaleas, the latter losing their leaves going into the colder months. Azaleas tend to experience a more prominent shift in seasonal color, although certain rhododendrons show this shift too. It is part of leaf senescence (aging) which includes autumn leaf color change; however, leaf color change is not a requirement.

It is worth noting there is oftentimes confusion when it comes to rhododendron and azalea fall foliage because gardeners will see the normal process of leaves turning color and dropping, which leads them to believe that their plants are not well.  Oftentimes, yellow leaves are the leaves that were produced earliest in the season. As leaves age they become less efficient at photosynthesis. Leaves have a maintenance cost and older leaves become a drain on the plant resources, so they change color and drop when it gets colder outside. Generally, if the leaves on the tips of your azaleas and rhododendrons are green and look ok, the plant is most likely healthy and will fill in with new leaves the following season when warmer weather arrives.

Rhododendrons that have small leaves are typically lepidotes. And nearly all lepidote rhododendrons change leaf color after the first frost of fall. Generally, as chlorophyll in leaves degrades- other colors are revealed. Therefore, the green foliage of summer fades and reveals protective purple, red and maroon pigments known as anthocyanins for winter. These anthocyanins provide increased resistance to the effects of freezing and chilling.

Rhododendron and azalea flowers are undeniably stunning in spring, but their fall foliage is beautiful as well and remains somewhat of a mystery. In the Medeiros Lab we continue investigating leaf efficiency and maintenance cost within this genus. We encourage visitors to stroll the rhododendron gardens and take notice of the wondrous display of fall foliage and consider the reasons why leaf color change happens too.