Garden Witch of Pittsburgh

Garden Witch Photo

The Autumnal Equinox arrived yesterday at 5:18 p.m. Also known as the September Equinox, it is a myth that the day and night are equal on the equinox. Another myth is that on the fall equinox, you can stand an egg on its end. A related folk tale is that it can only be balanced this way within a few hours before or after the precise time of the equinox.

While there is still light and warmth, autumn is a time of preparation to go to earth, to enter dormancy for winter’s rest. Recalling Greek mythology, autumn signals the time for the goddess Persephone to return to the underworld to live with her husband Hades.

To deflect attention from ancient Pagan celebrations of the equinox, the early Christian observances of Michaelmas (the Feast of Michael and All Angels) was scheduled on September 29, being close to the Equinox. At one time, it even was a holy day of obligation. Mabon, the second harvest, is celebrated by Pagans on the autumn equinox as one of the 8 Sabbats (celebrations based on cycles of the sun).

Garden Witch Photo

Fall is my favorite season. Watching trees, shrubs and other vegetation change color, enjoying brightly colored, sweet-tasting, ripened fruits; the crunch and smell of leaves underfoot, now that’s what I’m talking about! I especially like it when I drive through some leaves on the road and look through the rear view mirror and see them swirling around in the air disturbed by my car. Admit it, you know that you’ve peeked back at least once at leaves like this yourself.

Although plenty of people complain about raking leaves in the fall, probably even more of them enjoy driving around to look at the different colors. So many people do this that they have been dubbed “Leaf Peepers.” Throughout New England, it is the last gasp of the tourist season until there is enough snow for skiing. There are even websites with webcams to check on the progress of fall color to plan your trip at just the right time for peak brilliant color.

But what makes for good fall leave colors? Can it be predicted ahead of time? Do tree species turn the same color every year? Why do leaves change color?

Ye olde Garden Witch will provide some of the answers here. But for answers to all of these and other questions about the fall season, you’ll have to wait for when Phipps Conservatory & Botanical Gardens or a local Herb Group or Garden Club asks me to present “Falling into Autumn,” a fascinating look at leaf changes in the fall, basic leaf identification, and lots more.

Do tree species turn the same color each year?

Yes. Most tree species do turn the same color each year. During the growing season, the dominant green color of the chemical chlorophyll from photosynthesis masks the normal chemicals associated with the particular tree. When the tree stops photosynthesizing (making sugars) at the end of the growing season, the normal colors can then be seen.

The color red is associated with the chemical anthocyanin, and are the result of glucose that is trapped in the leaf when the connection to the tree veins is cut off. Yellows and oranges are already hidden in the leaves and are associated with carotin and/or xanthophylls. Brown is associated with tannins.

Evergreen leaves do not photosynthesize during the winter but are protected from moisture loss and extreme cold by having narrow, thin needle-shaped leaves. The needles shed year round, rather than all at once as deciduous trees drop their leaves. But there are two needle-leaved deciduous conifer trees that completely drop all of their needles every autumn. The Larch the larch (Larix laricina) and Dawn Redwood (Metasequoia glyptostroboides) both drop all of their needles each fall, both re-grow their needles the following spring, and both produce tiny cones.

Why do the leaves fall off?

When the growing season is over, the vascular tubes that carried water and nutrients between the leaf stem and tree branch are no longer transferring these substances, an abscission layer forms to separate the leaf stem from the branch since the connection is no longer needed, and the leaf falls off. After the leaf falls off, the markings from the leaf stem and veins (or tubes) result in what is known as a leaf scar, which can be used to identify trees during the winter.

Can color intensity be predicted ahead of time?

Cool nights and days with bright sun result in more red leaves. An early frost will kill leaves, they will simply dry out as they turn brown and fall off quickly. Some trees have combinations of color depending on light conditions. For example, maples often have more reds because they produce more sugar, but if there is not enough sun, or part of the tree is more shaded, then there is more yellow and orange.

One cool shrub.

When all of the other shrubs and trees are losing their leaves and have branches heavy with fruit in the autumn, there is one shrub that has the audacity to bloom and explode its seeds. More on this unique native plant later.