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Here Comes Color!

By Paul James

Celestially speaking, fall is inevitable, based on the manner in which the earth’s axis is tilted with respect to its orbital plane on or around September 21 or 22. But long range forecasts — at least to the extent you can believe them — suggest fall temperatures may not arrive until the end of the month, or perhaps even the middle of next month. So does that mean you should delay traditional fall gardening activities? No way!

Botanically speaking, most of the physiological changes plants undergo are driven by changes in daylength, not temperatures, so most plants don’t really care about warmer-than-usual fall temps. They may need to be watered more during dry spells, as in now, but otherwise they’re hardwired to do what their genetics tell them to do. This time of year, shorter day lengths of less than 12 hours trigger everything from fall color to flowering. The process is known as photoperiodism.

Deciduous trees and shrubs, for example, in response to shorter daylengths, cut off the flow of chlorophyll (the pigment responsible for green leaves) to their leaves, which allows other pigments such as carotenoids and anthocyanins that are already present to produce fall colors of red, yellow, and orange.

A number of flowers, including mums, will only flower when day length is roughly less than 12 hours. Any more and they won’t flower at all, although they can be tricked into doing so by manipulating light levels in a greenhouse. The same is true of Poinsettias and Christmas cacti, as well as rice, soybeans, and some onions.

But for gardeners, shorter day lengths mean there’s less time to get things done in the garden, which is the point I’m trying to make in an admittedly long winded and roundabout way. And among the things you should consider doing now are creating masses of fall color by planting trees and shrubs, mums, pansies, and flowering annuals of all kinds.

Because after all, the killing freezes of winter may not arrive until the end of November or even the middle of December. And that means more time to enjoy the amazingly beautiful colors of fall.

Happy gardening, ya’ll.

P.S. I may take some heat for suggesting you plant in the heat, but a century of weather data
clearly shows that temperatures are destined to cool soon. We may go through a very brief rough spot next week, but overnight temps are cooling off nicely, which means that although plants may stress out a bit during the day, they at least have a chance to rest at night. Just make sure you water well until daytime temps begin to drop.

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