Chlorophyll is replenished during summer but as autumn arrives and the days get shorter, trees start to seal off their leaves in preparation for harsher times ahead.  Chlorophyll production decreases and other pigments that are present start to become visible.  Depending on the tree these can include yellows, browns and oranges; reds and purples tend to occur where sugars are trapped in the leaves.  The brightest leaf colours appear before frosts when days are short and nights are cool.  Falling occurs when cells between the leaf and the stem start to elongate and break apart, triggered by autumn’s arrival or in stress conditions such as droughts.

Simple, yes?  All of these things are affected by weather throughout the season; sunlight, temperature and rainfall can all determine how our autumn colours appear and how long they last.  A really dry spring can result in early – and colourless – leaf drop because the sealing barrier between leaf and tree may have formed earlier than normal.  Colours may be muted if it’s been particularly wet during summer.  A sunny but cool run into autumn may produce early colour.  Really cold nights can result in yellow leaves; warmer nights can produce red colours.  Gusty winds and heavy rainfall as the leaves are turning may well bring them all to the ground before they’ve had chance to show off.

It seems that the perfect conditions for a beautifully coloured and prolonged autumn are a moist spring and dry summer followed by a dry autumn with warm, sunny days and cool, frostless nights.  That's not too much to ask for is it?