Matthew Stevens: 'Spooky season' is a season of change for outdoor plants

The calendar has just turned to October, and while that may mean the beginning of “spooky season” for some, it also means that cold nights are coming. It won’t be long until we have to start watching the news for frost alerts and guidance for protecting tender plants. Take some time to bring in any houseplants that are still outdoors and be prepared to protect any tender plants you want to try to squeeze a few more weeks of enjoyment out of. Inspect houseplants before bringing them indoors to make sure you’re not carrying along any undesirable pests with the plants themselves.

Along with the cold weather of fall comes a change in leaf color for many of our deciduous trees. There’s always something nice about the way the new colors paint our landscape this time of year. This change is not an accident of course; there’s a simple scientific explanation behind how and why it happens.

The changing of leaf color is caused by a physiological change that happens in the plant during fall. Leaves produce a number of pigments, the most well-known being chlorophyll. Chlorophyll is a green pigment and is the reason the leaves of most plants are some shade of green for most of the year. However, plants also contain carotenoids and anthocyanin, yellow and red pigments, respectively. The amount of each pigment a plant produces depends on the temperature and the length of day. For most of the year, leaves produce much more chlorophyll than these other pigments, but in fall chlorophyll production slows down and the other pigments take over. Trees that turn yellow or orange have a lot of carotenoids present, while those that turn red have a high amount of anthocyanin.

A number of other factors seem to play at least some role in how brilliantly the colors of fall shine in any given year. One is rainfall. Colors often seem to be more intense if the weather has been dry and sometimes aren’t expressed as vibrantly if there’s been a lot of rain. This can also dictate when the color change happens, as it may occur slightly earlier in dry years than in wet ones. The weather also affects our perception of the colors as well. Colors appear brighter to our eye on clear days than on cloudy ones, so if it is rainy during peak foliage season, it may not be as impactful to us as viewers.

Though we think of fall foliage primarily as a forest phenomenon, many of the deciduous trees and shrubs we use in our landscapes go through the same color change just prior to their leaf fall. Don’t neglect this characteristic when selecting plants to include in your landscape, as fall leaf color can have incredible ornamental impact at a time of year when flowers are sparse.