IN THE GARDEN Epic year for autumnal colour

Weather conditions mean autumn leaves are especially colourful this year

THERE has been a remarkable show of autumn colour this year and it has caught a lot of attention. It was good last year too but this is truly a vintage year. People go to the eastern United States to see the fall of leaves but it was not necessary to travel far this year, and it is still happening — there are a couple of weeks left in it.

The show of autumn colour was so good this year due to suitable weather since the end of May. There was a practically unbroken sequence of sunshine and showers all summer. Grass growth only slowed down for a couple of weeks in August, and tree growth did not slow down at all.

Trees grew at a phenomenal pace with near-perfect growing conditions. It was not a great summer for humans because daily showers do not suit holidaymakers, but it suits trees. The annual growth ring laid down by trees for 2016 will be massive. Many trees started secondary growth by late June. Also called ‘Lammas growth’, this usually coincides with the Lammas or Lughnasa festival at the start of August.

As summer faded, the good growing conditions continued into autumn with what must have been a record number of high-teen or low 20s readings of temperature. It was 17°C in Dublin on 14 November. There have been many sunny days and cool nights but no hard frost until a couple of days ago.

Sunshine packs the leaves with sugars and they last longer on the tree, but a combination of shorter day length and cooler nights causes the trees to withdraw the green chlorophyll into the buds, bark and branches and the underlying colour pigments of yellow, red and purple become visible. These are not as soluble and have to be jettisoned along with the leaf.

Losing leaves from many broad-leaved trees and some conifers, such as larch, is an evolutionary strategy to avoid desiccation during freezing winter conditions. Plants that stay evergreen are either originally from regions of warm climate, largely frostfree, or they have special features such as waxy coatings to resist moisture loss.

Some people have remarked that there are more fallen leaves this year — and there are. Growth of trees was so good that they just kept on growing and made long extended branches with more than usual numbers of leaves.

The last of them will not be down for a while yet, some alders are still green. Make sure to take leaves off lawns, driveways and paved areas.