In autumn, deciduous trees flaunt themselves in rich reds and golds. Gillian Vine explains why.
Deciduous trees drop their leaves to survive the cold of winter and the spinoff is splendid autumn colour in many trees, such as Central Otago's poplars.
A number of things affect leaf colour, some of them relating to the season, as trees react to the amount of soil moisture and temperature as well as shorter days.
The most important factor is the reduction in daylight, as deciduous trees, which lack the tough leaves of evergreens such as pines, realise it is time to start shutting up shop for winter.
What then happens is layers of cells form at the base of each leaf and eventually seal the tissues connecting leaves to stems and when this process is complete, the leaves fall.
Before the leaves fall, they age, pigments in them break down to reveal marvellous colours from the gold of oaks through crimson and purple maples (Acer).
Three chemicals are at work in determining leaf colour - chlorophyll, which gives green colour; carotenoids for yellow, orange and brown; and anthocyanins for red.
Warm sunny days and cool nights usually bring the best autumn colours.
Understanding the science is less important than deciding what will suit your garden.
This is the time of year to take a good look around and note which trees and shrubs colour well in your area.
This will help avoid the trap of deciding on a tree, putting it in and finding it hates your neck of the woods.
That is not to say you should grow only what your neighbour does but be aware if you stick your neck out, horticulturally speaking, there is always a bit of a risk that your experiment could fail.
On the other hand, you could start a neighbourhood trend.
