Saturday, October 10, 2009
The trees native to this island (shore pine and paper birch, red alder, a few Douglas fir, Sitka spruce, western red cedar and willow) are not known for their fall colour. But a suburb is like an etch-a-sketch. Shake it up, make it blank, and start again. Plant things that turn colour, things from Asia such as the Katsura, which turns yellow then hazard-orange, or Japanese maple, which reddens nicely.
A more subtle pinky-red is provided by this Asian dogwood, Cornus somethingorother.
And an addition from eastern North America--staghorn sumac, a sprawly shrub that gradually morphs to a spectacular crimson.
It's all about anthocyanins (when it comes to redness --yellows come from a different pigment). Turned blueberry leaves (in this case, highbush blueberry, Vaccinium corymbosum, also not native) are anthocyanin-rich. The reds and purples arise as air temperature declines, chlorophyll production tapers off (a result of the chill, in part), and relatively high levels of sugar remaining in the leaves react with proteins in the presence of sunlight. Long series of sunny days and cool nights produce the most striking colours.
Different varieties of blueberry turn different degrees of red. This can be seen within commercial blueberry fields where multiple varieties are grown side by side.
Direct sunlight is necessary. Where a leaf lies atop another, anthocyanin tan lines will result.
To sum up, plant foreign things that produce anthocyanins in the fall if you like red leaves. Or, move somewhere where such plants naturally occur.
P.S. A very good description of the physiological/biochemical bases of leaf-turning is this source.