Colourful autumn in store, says RHS The wet summer and recent warm, sunny weather means the UK could be in for an "incredible" display of autumn colours this year, experts said yesterday. The arrival of cold nights have prompted the first leaves to start to turn, according to the Royal Horticultural Society (RHS), and this year's conditions could deliver the perfect autumn. Wet weather earlier in the summer prompted trees to produce a large volume of leaves which they have retained, rather than starting to shed them early, as they would do in a dry year. And the recent warm, sunny days have increased sugar levels in the trees, which will boost autumn colours. So as chlorophyll, which gives leaves their green colour, begins to break down, exposing yellow, orange and red pigments, it could provide a "firework display from trees" this year, according to Colin Crosbie, curator at RHS Wisley. He said the recent very cool temperatures at night coupled with warm daytime temperatures had set the process of leaves turning in motion. And he said: "This year, we've had such a wet summer there's a large volume of leaves on the trees, and with the Indian summer, sugar levels will be high. There's the triggers for what could be described as the perfect autumn.