Reader's question: Graham, from Darlington, is enjoying the fantastic display of colour that the trees are giving us this year as the autumn marches on. He wonders if I could explain why the leaves, which start out as green, turn various shades of yellow, orange and red just before they drop off.

THE saving grace of the impending gloom of winter is the beautiful display that we are treated to by our leafy friends.

Light buttery yellows blend in with deep plums, coppery oranges and rusty browns. So, what causes the green leaves to change? Well, it is normally shortened daylight hours or a sustained change in temperature that triggers leaf drop, depending on the species.

The oranges and yellows are caused by pigments called carotenoids, which are present in the leaf to protect chlorophyll – the important green-coloured molecules that take sunlight and turn them into sugars, or food for the trees – from sun damage. They are in effect a sun block. In the autumn, the chlorophyll is no longer needed as there is not enough sunlight in the day to make sufficient food for the tree, so it goes into hibernation. The redundant chlorophyll in the leaves is broken down, hence the green pigment vanishes from them. This allows the orange and the yellow pigments to become visible.

The reds and purples, however, are caused by molecules called anthocyanins which are only produced at this time of year.

Scientists are torn as to whether the red colour is a defence mechanism to ward off insects, or whether it is part of the break down and reharvest of chemicals (because trees are recyclers too) within the leaf before the end is sealed and it drops off.

This is when the best bit of all comes, though... you get to run through the piles of crunchy crackling leaves and kick them high into the air, daring winter to show you its worst.

Jobs this week

■ Prune shrubs that have flowered over the summer and that have outgrown their space. Leave any shrubs that flowered earlier in the year, though, as you will only be cutting away next spring’s blooms.

■ Clean leaves and debris from ponds and put a net over it until the rest of the leaves have dropped from the trees.

■ Remove as much muck and grass from lawn mowers as possible. Give the blades a good oiling before putting it away in the garage for the winter.

Brigid presents the BBC Tees Gardening show on Sundays from 1pm to 2pm.

Questions can be answered on the day by emailing brigidpress@bbc.co.uk anytime during the week, or texting 07786-200995 and phoning 01642-225511 during the show.