Oct. 31, 2009

The river of leaves along the south side of the lane behind our block is brimming this year, evidence that the world is evolving as it has for eons. Or, at least for the 10 years or so we’ve lived here.

Except, the Evans and Nanking cherries still have green leaves.  Same with the mountain ash down the block. And the 15-metre columnar aspens were still full of leaves earlier this week, but they’re brown. Same with the Hawthorne.

No reason to expect that in a strange year in the garden, when we had June frosts, a cool-wet growing season and record high temperatures in September, that autumn would be normal.

Ever recall when leaves didn’t turn fully yellow? It’s the first time in the 30 years he’s been here that John Gilbert, arborist for the City of Lethbridge, hasn’t seen much yellow. Oh, he may still see weeping birches with most of their leaves, sort of yellowish, but not the usual brilliant fall colour.

What happened? The temperature dropped to -17 one night around Oct. 12, stopping the normal process in the abscission layer at the base of the leaves.

As the U.S. National Arboretum explains, verified by John Gilbert and friend Clive: “When nights reach a threshold value and are long enough, the cells near the juncture of the leaf and the stem divide rapidly, but they do not expand. This abscission layer is a corky layer of cells that slowly begins to block transport of materials such as carbohydrates from the leaf to the branch. It also blocks the flow of minerals from the roots into the leaves.

“Because the starting time of the whole process is dependent on night length, fall colors appear at about the same time each year in a given location, whether temperatures are cooler or warmer than normal.”

Since the deep frost stopped the colour transformation from happening to a large extent, it’s simply a strange phenomenon, but not likely to hurt the trees.

”It’s just Mother Nature taking care of itself,” says arborist Gilbert who was planning to continue watering in city trees until today, as he usually does. Trees and bushes in our yard got a good drink this week too. They’ll need it again come winter.

Another effect of the Oct. 17 deep freeze seemed to be a mass, simultaneous leaf drop – still green – from some lilacs. And with other trees, you can’t pull the leaves off.

Makes it all confusing for those accustomed to raking or otherwise gathering leaves through October.

Around our place, they gather from other folks’ trees both east and west of us. No problem, except they never fully get picked up, often pushed around by the snow shovel. But by next spring, they still make good compost. I still have a bag from a couple of years ago that contributes to the composter.

Also works well to just dig the leaves into the garden.

The rest sit in paper bags atop the leaf river in the lane for the city’s residential fall leaf collection. The lane leaves will have to await a warmer day and drying wind.