The leaves still cling to the trees, immersed in the process of shedding their emerald green tones for the vibrant warm colors they don for the fall.
The process begins as cooler weather and shorter days signal the trees that winter is approaching. The trees in turn begin breaking down their chlorophyll, the green pigment responsible for capturing energy from the sun to be used in the sugar-making process. The tree then reabsorbs the chemical building blocks of the chlorophyll for use during the winter and for the re-leafing process next spring.
As the chlorophyll fades, the other pigments in the leaves that can’t readily be seen while the chlorophyll is in place, become apparent. These pigments — reds, yellows, and oranges — don’t break down as readily as the chlorophyll does. Each tree species has a different specific combination of pigments in their leaves, giving them their own specific color. White oak leaves are a yellowy-orange, ginkgo trees turn bright yellow, and dogwood and Bradford pear trees turn a deep maroon color. Sugar maples are my favorite, as they have deep orange leaves with a spattering of red and yellow.
Most people don’t realize that the pigment colors that you see in the leaves are the same that you see in flowers and in the food that we eat. Most of the pigments are in a group called carotenoids. The yellow of a ginkgo leaf is the same pigment as a daffodil and a golden delicious apple. The orange of the sugar maple is the same as the orange of a daylily and a carrot. The red of a scarlet oak leaf is the same as a rose and a tomato.
Eventually the trees shed their leaves in a process called abscission, where a barrier is built between the leaf and the tree. Most leaves fall to the ground at this point, but some like oaks and beeches hang on through the winter. They are still detached from the tree’s vascular system, but they hang on until they are pushed off by new growth the next year.
So, as it turns out, the process of changing leaf color in the fall is all about recycling nutrients to feed the plant through the winter and save different molecules for next year.
Now, while the upper part of the tree may go dormant in preparation for the harsh winter, it doesn’t mean that the whole tree has gone to sleep. Fall and winter (when the ground isn’t too cold) is an ideal time for trees to grow roots.
To take advantage of this period of root growth, the fall is a great time to plant or transplant deciduous trees and shrubs. I get lots of calls throughout the year asking when is the best time to dig up small trees and shrubs and transplant them in the landscape. My answer is always to wait until just after the leaves fall in the autumn.
Digging up and transplanting a tree or shrub is a source of stress for the plant — it damages the roots and can cause the plant to go into a shock. Leaves can be lost and growth slowed until the plant has recovered. The effect is reduced in trees and shrubs that are dormant, so planting in the fall can help plants get off to a better start. In addition to the lower amount of stress the plant undergoes, planting in the fall allows the tree or shrub to take advantage of the period of good root growth in the fall and winter.
After transplanting, you’ll want to make sure that your newly planted or transplanted trees and shrubs receive plenty of water. That means that if we have a dry week, you’ll need to drag out the hose and water your newly planted trees. This is the most important step in assuring success.
I would also suggest a soil test prior to planting, to make sure that all nutrients are in balance. Growing roots do require good nutrition, especially phosphorous. However, this doesn’t mean that you automatically fertilize trees and shrubs when you plant them. And you never want to add fertilizer directly to the planting hole. Instead, do a soil test to see if you need to adjust your fertility to the right level — adding fertilizer when it is not needed can cause more problems than it solves.