Dim and Dimmer

January, 2012

PICKAWAY TO GARDEN

Dim and Dimmer

By Paul Hang

Last month the theme was the dimming light as the Winter Solstice approached. Now that it has passed, light, or the lack of it, is still on my mind. As the earth continues its annual revolution around our Sun its axis begins ever so gradually to point towards our greatest natural source of light. That's the good news for us in the northern hemisphere. The days are getting longer. The bad news is that the warmth lags the light. We still have more cold weather ahead. This dim light, plus the permanent overcast over the states surrounding the Great Lakes, causes dimly lit days.

For plants light is essential, along with water, warmth, a place to grow and the necessary nutrients. Given that the light is dimmer I have been reading about it and its effect on plants. I guess you could say that "absence makes the heart grow fonder." In "Botany for Gardeners" Brian Capon discusses the fascinating, to me at least, science of plants. If you can't grow them you can read about them. It turns out that the physiology of plants is just as intricate and complicated as our own, if not more so.

As I dimly understand it, plants, as well as teenagers, have raging hormones. Two hormones in sun-loving plants are especially affected by light. The process of plants growing towards the light is called phototropism and it is caused by hormones.  Auxin is a hormone which causes cells to elongate. When light strikes a plant from above the auxin is equally distributed across the stem resulting in straight growth. Light striking one side of the plant causes the auxin to migrate to the shaded side. This causes the cells to elongate more on the shaded side than on the lighted side. This causes the stem to bend towards the source of light.

Growth of the stems between the leaves is caused by another hormone called gibberellin. The action of gibberellin is affected by the intensity of light. When the light is intense stems grow slowly spacing the leaves to promote a squat stable strong plant. In low light gibberellin becomes more active causing the stems to elongate.  The plant reaches for the light stretching the leaves up to better catch the light. This may help a plant in competitive situations to outgrow its neighbors.

In extremely low (dim) light gibberellin's uncontrolled effect results in leggy, weak plants trying desperately to reach the life giving light. The plant can get so tall and spindly it can't stand up and falls over. The result is often the death of the plant. Interestingly shade loving plants have evolved to show no such reaction to low intensity light.

These processes are familiar to anyone who has observed plants' growth. Although science can inform us about this it still hasn't been able to fully understand it. How do these hormones "flee" from the light? We don't know.

Houseplants are particularly susceptible to these effects. As the light dims outside it grows even dimmer inside and plants respond. Plants near a window "reach" for the light and the stems curve. That's auxin. Dim light from above results in elongated unstable plants. That's gibberellin. To keep our over-wintering and house plants healthy and attractive we need to take account of those raging hormones.

Turn plants every week or so to keep them balanced and from growing only on one side. Pinch back leggy growth. Provide artificial light to mimic the longer days that are only a dim memory. If you do these things and cut back on the fertilizer your plants will do fine until the light returns.

January begins our calendar year. The full moon occurs January 9, 2012. Although the light is dim we can take comfort in the fact that it will not get dimmer. Longer days are coming! The sun returns and with it we, and the plants, will begin to rouse from our winter slumber, but not just yet.

Things to do in the garden:

The list of things to do in the garden has gotten shorter. Things we can do about gardening can fill those idle hours, if you have any.

Learn to sharpen your tools, trowels, pruners, spades and if you are really adventurous, your mower blades. It's always a good idea to consult the experts. Go on line and google it.

Review last year's garden. Draw a map while you can still remember what grew where.

Check your supply of old seeds. Are they expired? Do you want to reorder that variety? Read your new seed catalogs and begin to plan next year's garden. Order seeds now, especially the new varieties. They usually sell out quickly.

Believe it or not, by the end of the month, you can begin to grow members of the Allium family; Onions, Leeks, Garlic and Shallots from seed. You can get ready by getting your seed starting supplies together. Make sure you provide plenty of light.

Check your houseplants for bugs and overall health. Are they getting enough light? South and west facing windows get the best light. Place as close to the window without touching the glass. Cold windows can damage plants. Try using a grow light but don't use a dimmer.