I have a vine maple tree whose leaves turn a very plain, rather ugly brown in the fall. It gets full sun from about noon until sunset. From what I have read, its leaves should turn red, orange, and yellow. What can I do to trigger this? I am thinking of how Hydrangeas are different colors depending on the acidity of the soil. I would like a tree with attractive fall color. I have also read it likes moist places in the shade, and it has not had that environment in my yard. Could the amount of water it gets in the summer, or lack of water, be affecting this?
According to J. Harris in The Gardeners Guide to Growing Maples (2000, p. 119),
“Autumn color is due to a chemical change in the leaves and a combination of the
remains of the chlorophyll grains and a substance called anthocyanin. The
color assumed by leaves depends on soil and air conditions and on the amount
of moisture. If conditions are very dry in the autumn, then the color will
not last for long. After a frost, colors appear more intense, but the frost
can check activity. It will also not be so good in very wet conditions.”
The National Arboretum provides a complete explanation of why autumn
leaves turn color.
There is an excellent article from the Seattle Times (September 25, 2008) in which former Washington Park Arboretum Collections Manager Randall Hitchin describes this process. Fall leaves change color during “the final stage in the life of a leaf. [This] has to do with four groups of pigments. You know about chlorophyll, the green chemical that does all the heavy lifting spring through summer. Then there are the carotenoids — carotene and a suite of related compounds — that give leaves yellow and orange coloring. Tannins produce the russets and browns. Finally, anthocyanin provides the classic autumn colors of red and purple. During the growing season, chlorophyll dominates. It’s constantly being made to replace what’s degraded by ultraviolet light, and the leaf appears green. Depending on tree species, yellow, orange or brown pigments have been there all along, concealed by green chlorophyll. In autumn, as chlorophyll production slows and ultimately stops, the yellows, oranges or browns emerge. Anthocyanin is genetically controlled, so some tree species get red and some can’t. Unlike the carotenoids, anthocyanin isn’t usually present during the growing season, but is produced in leaves with fall weather conditions. In trees that can go red, the amount of it depends on environmental factors. In ideal conditions, you see vivid pinks, reds and purples — that ooh-and-ah factor. […] The Northwest autumn is often overcast or rainy with only minimal cooling at night; not optimal for fall color. Another reason has to do with numbers. In the Northwest, the effect of color is diluted because of species composition in our forest canopy, which is typically dominated by evergreens. With the evergreens outnumbering the changing deciduous trees, you don’t get those huge sweeps of colors you see back east.”
There are other possibilities why your vine maple is not producing good fall
color:
1. It might be getting too much light. The natural habitat for the vine maple is
under an overstory of large conifers (Japanese Maples, by J. Vertrees,
2001, p. 247). Afternoon sun is the most intense and could be stressing the
tree. Harris (2000) notes that while tree-like species prefer open sites, woodland conditions and dappled shade are ideal environments for shrubby maples. (Harris., p.
118).
2. Other than light, the environment might be a little off. Vertrees (2000, p. 247) notes that with vine maples, intense color does not develop in environments where abundant moisture and fertility keep the trees from being under stress, i.e., they need stress to produce good color.
3. Trees of the same species will exhibit different fall colors depending
on the growing environment and peculiarities of each individual tree. (As
identical twins can be quite different). When selecting a tree for fall
color, it is best to first view it in autumn — then remember it will change
somewhat when it is installed in a new home.
It is not likely that changing soil pH will have an effect. I have been
disappointed in fall color a couple of times and finally replaced the
trees — after viewing them in full color in the nurseries.