The effects of shortening days, lower temperatures

Published 3:42 pm Friday, September 27, 2019

The signs of shortening days are beginning to show even if the accompanying lower temperatures are running behind.

Both my hens have quit laying and are molting, i.e. shedding some feathers. The green ash trees out front are molting too, having shed a third of their leaves already. In the coming weeks shorter days will reduce chlorophyll production and that green pigment will get overwhelmed in many tree species as pigments of the fall colors come to the forefront.

The fall pigments have been there all along, just masked over by the green. A few plants will move toward bloom as less sunlight gears up reproduction in them. For these plants, it is actually the increasing daily period of darkness that triggers bloom, not the decreasing amount of light per se.

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Among the short-day plants we know, surely the best known is the poinsettia. That one insists on more and more total darkness to do its Christmas thing. Just a tiny, short flicker of light at the wrong time dooms blooming and the red holiday bracts around the blooms.

Most of us probably don’t think about a role for light in the sprouting of seeds. That’s because the seeds of most plants don’t need light to germinate. They merely need the right temperature range, decent moisture and a few days of both to sprout. They germinate in darkness, either underground or down in a pot or tray of some kind. But there are species with seeds that must get light to germinate. And some species merely don’t care: dark or light matters not to their seeds. It all goes back to the original ways of plants before we humans took to gardening and farming.

All the seeds that require some light to sprout are very small seeds. That makes sense because the smallest seeds cannot make it up planted down deep and dark like larger seeded species. Small seeds do not contain enough stored food for the energy to push up through an inch of soil. We like to plant seeds as deep as practical because that somewhat prevents them from being eaten by wildlife. Also, soil moisture lasts longer down there as opposed to close to the surface.

In nature, most seeds are dropped on top of the ground.

Other than a few seeds buried by squirrels or other critters for later food, wild seeds have to sprout on top of the ground with maybe a layer of damp leaves helping out. But even if a thin layer of soil or debris covers seeds, light does penetrate a bit.

Among the plants with seeds that require light to germinate are lettuce, poppies, impatiens, petunias, snapdragons, begonias and coleus.

There are seeds or other species that can usually be counted on to sprout when sown on top of the ground but they don’t require light to germinate. They are just small, relatively fast germinators like cucumber, mustard and turnip. For these, gardeners like a shallow planting with soil firmed up to keep the seeds moist.


Terry Rector writes for the Warren County Soil and Water Conservation District.