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Volume 16, Issue 43 - October 23 - October 29, 2008
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The Bay Gardener by Dr. Frank Gouin

Coloring the Leaves

Moist summers and dry falls turn up the color quotient

We Easterners are fortunate in being surrounded by a large number of hardwood species that have the potential of displaying an abundance of colors from yellow to brilliant red. The colors that each tree species develops in the fall are genetically controlled. However, the intensity of the colors is determined by growing conditions.

In New England and in colder regions, including western Maryland, sugar maples and red maples abound, and their colors are a brilliant red to orange.

The bright yellow colors are provided by birch, ash and poplar trees.

Here in southern Maryland, the tupelo, black gum, dogwoods, scarlet oaks and red maples provide us with a variety of red colors, while the tulip poplar, river birch and ash provide an abundance of yellow colors.

When fall coloring of the foliage occurs is dependent on day length and drop in temperatures.

As daylight hours grow shorter, the growth of plants slows and they begin preparing for the cold winter months. For deciduous trees such as oaks and maples, growth ceases, the buds in the axils of the leaves develop heavy bud scales on the outer surface and nitrogen begins the slow process of moving out of the leaves, accumulating around the buds on the new stems.

The nitrogen that is moving out of the leaves into the stem is the result of the natural destruction of the chlorophyll within the leaves. As the chlorophyll breaks down, the colorful pigments called carotenoid and xanthophyll — which have always been present in the leaves — appear. The genetics in the plants determines which pigment is prominent. An early frost can hasten the color change but can also cause premature leaf drop.

The intensity of the colors, however, is determined by environmental conditions such as how much precipitation, when and with what temperatures. If we have a wet or moist growing season and have a dry fall, we will have bright colors. If we have a dry summer and a wet fall, we will have much more muted fall color. If we have a dry summer and dry fall, the fall foliage season will often be shortened.

Most interesting of the hardwoods is the scarlet oak. On the average of about once in five to six years, the scarlet oak will develop its most attractive penetrating scarlet red color. For this to occur requires an almost perfect growing season followed by a cool dry fall. Under these conditions, nearly all of the scarlet oak will turn a brilliant red from top to bottom and retain the color for at least two weeks. When I see this happen I say to myself, it was a good year.

Ask Dr. Gouin your questions at [email protected]. All questions will appear in Bay Weekly. Please include your name and address.

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