Autumn is coming into its full glory with a striking array of colours

Autumn can be a busy time for a gardener; it’s a time of change, with shorter days and falling temperatures. Summer jobs such as watering, weeding, feeding and mowing are swapped for jobs of a more preparatory nature. Autumn tasks include cutting back, lifting and dividing, not to mention the dreaded leaf clearing.

At RHS Garden Harlow Carr, as the summer ends and the autumn begins, gardeners and visitors begin to wrap up warm as a guard against the impending cold and wind. The garden becomes quieter: the hum of lawn mowers reduces, and bird song diminishes. There is a brief lull, a few mushrooms pop up, wind blows and twigs snap. Then all of a sudden, we are presented with an awe-inspiring show of colour, but not from flowers and plants – in autumn, the trees are the stars of the show! An explosion of colour erupts from the woodland canopy: flame-like reds and oranges, cooler lemon-yellows vie for attention against the richer, buttery tones. Trees that have been quite indistinguishable during spring and summer suddenly reach the top of the must-see list.

So why is it that some trees such as alder and ash have leaves which fall when they’re still green, whereas others produce a range of vibrant hues, from bright yellow through to orange and red?

The answer lies in their function. Leaves are small power plants; their main role is to convert carbon dioxide into sugars, using the energy of the sun together with a green light capturing pigment known as chlorophyll. This process is known as photosynthesis. Sunlight is made up of a wide spectrum of colours, as seen in a rainbow. The process of photosynthesis is driven by blue and red light; it is these colours that the leaf absorbs. The remaining unused green light is not absorbed and is instead reflected back (into your eye), causing all plants and leaves to appear green.

As autumn progresses, trees detect the reduced sunlight levels, shortening days and dropping temperature. There is no longer enough light or water for photosynthesis to occur. The tree begins to break down and re-absorb all useful substances from the leaf such as proteins, sugars and chlorophyll. At the same time, the leaf is filled with any waste products the tree wants to get rid of such as heavy metals. Pigments that are normally present within the leaf but masked by the green chlorophyll are revealed. Yellow pigments (xanthophylls), orange pigments (carotenoids) and red pigments (anthocyanins) now show through. The brown colour so familiar to the often overcast and grey Britain is actually due to the pigment proanthrocyanins that gives wood its colour.

My personal autumn colour favourites are:

The reds: Trees such as maples and oaks are well known for having strong red leaf colouration. Euonymus alatus ‘compactus’ and Liquidambar styraciflua (sweet gum) look particularly good. At Harlow Carr Vitis coignetiae (crimson glory vine) has the most show-stopping red winter colour. This

grape vine relative has large, slightly lobed leaves which turn scarlet in September; it entirely swamps the large oak tree it grows upon and it is located at the northern end of the Streamside. It’s well worth checking out.

The yellows and golds: This group is well represented by birch and cherry trees. Some notable specimens include Gingko biloba (maidenhair tree), Parrotia persica (Persian ironwood) and Liriodendron tulipifera. Ginkgo leaves continue to look amazing after the leaves have left the tree, carpeting the ground completely with a mass of yellow leaves. The most spectacular of the yellow trees are the Betula lenta (sweet birch); a group of these trees are planted deep in the woodland glade at the top of the garden. They have brilliant colour but don’t last long, so be quick.

The oranges: This colour group is best represented by the magnificent Cercidiphyllum japonicum (katsura tree) which in addition to orange and pink-flecked yellow leaves, gives off an intense perfume of burnt sugar as the leaves degrade. Acer palmatum ‘Sango Kaku’ (coral bark maple) and Castanea sativa (sweet chestnut) are other good examples of orange winter colour.

Finally, the browns: This is perhaps not the first colour that jumps into one’s mind when thinking of autumn leaf colour. Metasequoia glyptostroboides (dawn redwood) turns a distinctive coppery pink colour. Its close relative Taxodium distichum (swamp cypress) has been described by one gardener as big ball of rust; it certainly does stand out.

Autumn is a fabulous time of year to be in the great outdoors – make sure you step outside and soak up the vibrancy and colour of this spectacular season.