Today the day length is 11 hours 46 minutes. Why does a gardener
spend time focusing on the length of day? It is because the
plants do. Why do they? It is because the length of daily light
compared to the period of darkness directs the daily function of
plants. In our part of the world, leafing out in the spring,
flowering, seed set, leaf color change, and leaf fall in autumn
are all determined by day length. Thus it should be no surprise
that particularly woody plants begin to prepare for winter
starting June 20, the date of the summer solstice. The
construction of a wall called the abscission layer, where the
leaf stem (petiole) joins the twig, first inhibits and finally
cuts off the flow of sugars from the leaf to the remainder of
the plant. This barrier is functional and necessary so that when
leaves detach from the plant, an open wound is not left. The
leaf itself contains a green substance, chlorophyll, where
carbon dioxide and water in the presence of sunlight are
converted into simple sugar that is th