Summer has officially come to an end, but while March 1 signals the change of season, it also welcomes a good time to plant. Hopefully we have had a bit of rain in some areas to increase soil moisture and temperatures in the soil are still very good for root growth. So, what do we plant? Consider planting something to give a show in the coming months when many plants are looking tired and the showiest plants in the garden are coming to an end.
Deciduous trees and shrubs really come into their own in the autumn, offering spectacular displays. No one can dispute that a whole tree or shrub dramatically changing colour is a showstopper. We often accept it as natural, but it gets even more interesting when you look into why a plant changes colour.
To understand it we need to get back to the basics of how plants make food. Plants have a green pigmentation in them called chlorophyll that is vital in the process of photosynthesis. This process turns sunlight into energy that is stored as sugars to feed the plant. Plants with coloured leaves, other than green, all have chlorophyll present as it is essential for growth, but in small enough quantities as not to be seen. The reverse is also true as many green plants have beautiful coloured leaves, but high quantities of chlorophyll masks the colour.
There are many pigments involved in leaf colour, but the main ones are anthocyanins and carotenoids. The anthocyanins cause the purple and red colours in leaves, and are sensitive to pH levels in the cells. The more acidic, the brighter the red colour; the less acidic, the tendency is towards purple. Carotenoids give the yellow and orange colouration, and are present in most leaves all year, but are masked by the green chlorophyll. As autumn sets in, the nights become cooler and the days get shorter, and chlorophyll concentrations decrease. This is when deciduous plants show their brief, but often dramatic, true colour.
Some years the display is better than others, and this is dependent on the weather in the build-up to autumn. Night-time temperatures need to be cool, but not freezing, as frosts will begin to destroy the cells and cause them to turn brown. Sunny days will help increase the level of carotenoids, intensifying the display. In dry years, stress to plants can cause early autumn colour, but conditions that are too dry often result in premature leaf drop or browning. If conditions are right, displays can last weeks or even months.
The choice of plant is important as some are much more reliable than others and just because it is deciduous certainly does not mean you will get the desired display. One of the best-known groups of plants for reliable autumn colour is the maples, with a huge range from which to choose. All sizes, shapes and colours are catered for in this diverse group.
Another reliable group of plants are viburnums. These are often very tough and resilient to a wide range of conditions, and, in addition to autumn colour, have beautiful spring flowers and often berries. If you can choose a plant that will produce more than one display a year, no matter the size of your garden, you get better value for money.