Tuesday, September 4, 2012

Early Leaf Color is Drought Related by Mary Small

When fall coloration appears early, like this year, it usually means plants are stressed.  Many factors can stress trees, but in 2012, the likely culprit is the weather.  Conditions in the Denver metro area have been dry since fall of 2011.  March, June and July were warmer than normal months.  

The excessive heat and dry conditions can kill roots or stress them.  When roots are stressed they can’t absorb water well from the soil.  Tree leaves still continue to transpire (lose moisture to the surrounding environment) and the poorly functioning roots can’t supply the need.

During the growing season, trees are constantly making and breaking down chlorophyll (the green plant pigment) to produce starches and sugars, their “food”.   When a plant is stressed, it can’t produce as much chlorophyll, so the green color fades, allowing other pigments to show.  (These other pigments are always present, but masked by the presence of chlorophyll.)  So reds, oranges and yellows begin to appear even though the calendar tells us the normal leaf coloration period is a ways off.  

You can apply water to help improve plant health, although it won’t reverse leaf color changes now.  Be sure to provide water this fall and winter to help already stressed plants survive the winter. This fact sheet  http://www.ext.colostate.edu/pubs/garden/07211.html