Where is Jack Frost?
He is late–in previous years, he always came around 8 October, my mother-in-law’s birthday.
Actually, it’s not Jack Frost that causes leaves to turn color.
What causes leaves to turn color in the fall? Shorter day lengths and cooler temperatures trigger the leaves to discontinue the production of chlorophyll, allowing other pigments to shine through. Sunny days stimulate the manufacture of carbohydrates and cool (40-45° F) nights allow the carbohydrates to break down into sugars. The more bright sunny days and cool nights we have, the more brilliant the autumn colors. Adequate rainfall is also necessary. In a dry summer and fall, the leaves turn brown instead of red or yellow.
For the most part, golden leaves appear earlier than red leaves.
Carotenoids color pumpkins, carrots, corn, and sunflowers, and provide yellow and orange pigments to the leaves.
The Natural History of the Senses
One of the earliest to color is the ubiquitous Honey Locust (Gleditsia triacanthos). A legume, the doubly-compound leaves become a blaze of golden-yellow early in October. The leaflets are so small they don’t need to be raked when they fall; they simply blow away.
This native tree, minus its thorns and long seed pods, was refined to take the place of the American Elms killed by Dutch Elm disease in the 1950‘s. It grows fast to a height of 30-50’.
Kentucky Coffee Tree (Gymnocladus dioca) is also a legume with golden, doubly compound leaves in Autumn. These leaves can, however, reach up to 36” inches in length and 24” in width.
Growing 60-90’ tall, this handsome tree leafs out late–very late (Its Greek genus name, gymnocladus, means “naked branch”.) The female tree flowers and produces picturesque seed pods that last all winter; the male tree produces far less–for that reason it is preferred for street planting–see above. (I myself, prefer the flowers and pods.)
Not many people know of this tree, but it is a superior tree in every way, attractive all four seasons. It needs full sun and makes a splendid lawn or street tree. I had one growing in the tight space between two driveways at my townhouse, visible through both my living room and bedroom windows and it was delightful every single day that I lived there.
In spite of its name, it is native to the Midwest. it is rare in the wild, but can be found along streams and in floodplains.
The large heart-shaped leaves of Redbud turn to a glorious gold early in the fall. A fast grower, its spreading crown grows wider then tall, creating a delightful umbrella under which to sit. Another legume, It is an understory tree, found in the shade of larger trees in dry-mesic soil in open woods or savanna. It is common in woodlands just south of Chicago, but rare to the north. It is also compatible with Black Walnut trees.
An open grown Black Walnut tree (Juglans nigra) is magnificent–it can grow as tall as 100’ with an equal spread. The compound leaves turn a glistening gold in October, a standout when viewed against a brilliant blue sky.
It does, however, have a bad reputation. Many people think that the juglone produced by the roots is poisonous to all other plants, but that’s not true. Members of the Rose family–rose, potentilla, spirea, chokeberry–and the nightshade family–tomatoes, eggplant–won’t grow within its root zone. In my experience, Witch Hazel (Hamemelis virginiana) is incompatible, also. But all other native plants, to the best of my knowledge, that grow in woodlands will grow under a Black Walnut.
A close cousin of the more common Sugar Maple, Black Maple (Acer nigrum) can be identified by the drooping edges of the similar looking leaf. It is, indeed, a majestic tree; the brilliant gold leaves are as eye-catching as the scarlet leaves of Sugar Maple. Black Maple is found in rich woods and further west than Sugar Maple into Minnesota, Iowa, Kansas, and Arkansas and said to be more tolerant of heat and drought than Sugar Maple. Swink & Wilhelm surmise ‘that it was the principle “sugar tree” in our prairie provinces prior to settlement.’
I can only recall seeing only 3 Black Maples in my life: one at Cantigny, a park in Wheaton, IL., one in Geneva next door to a client of mine, and this one at the Frank Lloyd Wright Home and Studio in Oak Park where this photo was taken.
The rounded, oblong leaves of Witch Hazel (Hamamelis virginiana) turn to a luminous gold in the fall, while a stunning surprise waits for us in November. (stay tuned) It is an open, multi-stemmed shrub or small tree, up to 18’ tall. It is common in the high dune area, in rich woods, and the slopes of ravines on the west side of Lake Michigan. it’s easily obtainable in commerce.
Spicebush (Lindera benzoin) . Ginny Umberger sent away for 5 Spice Bushes many years ago and they have thrived in her back yard ever since. But they aren’t aways that easy to grow in our area–I planted one here and the top half died the first winter; the bottom half the second. This photo was taken at Potawatomi Park in St. Charles in a partially shady, moist soil situation, which is what it requires in order to thrive. It is dioecious (separate male and female plants), but is more likely to increase clonally. Rarely found in nature in NE Illinois, it is absent in NW Illinois altogether, but common in southern Illinois. The caterpillars of Papilio troilus (Spicebush Swallowtail) feed on the leaves.
The fan-shaped leaves of Wild Black Current (Ribes americanum) turn to gold and brass and copper in the fall. It’s distinguished from Buffalo Current (Ribes odoratus) by its “gorgeous, golden, globular, glistening, glittering glands” on the lower leaf surface, visible only with a 10+ hand lens, declare Swink & Wilhelm in Plants of the Chicago Region. These shrubs, situated next to the building at Potawatomi Park in St. Charles, grow to 5‘ tall and around. In the wild they are found in moist or upland woods.