All throughout winter, some evergreen plants – not conifers — hang on to their leaves but I have observed that they activate their own unique winter protection. I am speaking of two plants that I am growing for the first time. One is a herb, mountain savoury, growing in a large frost-proof pot near the house wall, and the other is an azalea, also growing in a container with other similar small-leafed azaleas. The companion azaleas, curiously, do not change their leaf colour at all over winter. The leaves of the savoury and this particular azalea take on a purple colour. The savoury’s are rich and intense, while the azalea’s are a dark blue-purple, and up close, the leaves look spotted with pewter. Now that it’s spring, the azalea’s leaves have reverted to green, perhaps to supply energy (chlorophyll) for the numerous flower buds in the process of forming. The flowers of this particular azalea are blue. The other azaleas whose leaves remain the same green all winter long have red and orange blooms. The savoury’s leaves, however, are still purple, though new leaves are emerging a pale green. And I note that there are tiny hairs on the winter leaves — additional protection over winter, like “fur.”
In an earlier post I focused on the pinky-orange emerging leaf buds of roses. And even when the leaves are fully out, some roses retain their reddish colour for quite some time, perhaps until the plant starts to absorb enough of the right wavelength of light to manufacture sufficient chlorophyll. The rose in the photo only gets direct sun past noon.
The mahonias too show the same striking colour pattern: they leaf out in sumptuous colours of red and orange in spring. And in autumn they put on a similar stunning repeat performance. The leaves exposed to a greater amount of sun display more brilliant hues than those which only have sun from noon onwards.
The exception to these colour changes, from green to purple or red, is the willow. In early spring, the fuzzy catkins of willows are always charming. The “fur” of pussy willows is their protection against spring’s widely fluctuating temperatures, often over more than 20 degrees, such as the other day’s early morning frigid 2 C which rose by mid-afternoon to a summery 24 C.
I am guessing (and further reading may confirm this) that overwintering leaves owe their unique colours to phytochemicals – antioxidant flavonoids most likely, the same ones that colour the petals of their flowers as well. I have yet to see whether the mountain savoury’s flowers are blue, echoing the blue azalea’s flowers and purple winter leaves. And again I would assume that these captivating colours play a role in protecting these plant parts from not only extremes in temperature but perhaps, because of the increased concentration of chemicals, as well from predation by insects and animals starved for greens throughout winter. But what triggers the white fur in pussy willows in the spring, I wonder?
Leaf colours other than green in the winter – they’re not just for cosmetic or aesthetic purposes; they’re highly functional as well, protecting leaves from all sorts of damage. Ah… nature and her mysterious ways — truly amazing!