UNITED STATES—Autumn does not get cool enough locally to prevent everything from blooming. A few plants can bloom sporadically all year except only during the coolest part of winter. A few plants naturally bloom in autumn. Cool season annuals begin blooming before warm season annuals finish. Flowers can potentially provide plenty of autumn color if necessary. A mild climate can be a major advantage.
It can also be a disadvantage. Minimal chill causes deciduous foliage to start to get messy before it starts to get colorful. Some deciduous plants shed completely before getting chilled enough to develop appealing autumn color. A few others do not even get cool enough to defoliate completely. They instead retain their shabby old foliage through winter until new foliage replaces it in spring.
Nonetheless, several adaptable deciduous plants get sufficient chill to develop impressive autumn color here.
Foliar autumn color is not exclusive to New England.
Sweetgum, Chinese pistache, flowering pear and ginkgo are likely the four best deciduous trees for autumn color locally. Sweetgum and Chinese pistache produce the most impressive ranges of vibrant colors. Flowering pear is comparable, but with less yellow, and more rich deep burgundy red. Ginkgo lacks such range of color, but develops the brightest and clearest yellow autumn color.
Boston ivy, crape myrtle and persimmon get about as colorful as sweetgum, even if incidentally to their primary duties. Crape myrtle is popular for its abundant and richly colorful bloom in summer. Persimmon is a fruit tree. Boston ivy obscures graffiti and helps muffle sound on freeway soundwalls. Cottonwood and black walnut turn bright yellow, but in the wild rather than in refined gardens.
Even for the locally mild climate, there are plenty of deciduous plants that provide foliar autumn color. Trees are the most familiar. Vines and shrubbery are also popular. Because this mild climate is marginal for some of them, color is likely to be variable from year to year. Unfortunately, some that perform satisfactorily for inland locations may perform less satisfactorily in coastal conditions.
Where autumn chill is minimal, the best and brightest yellow autumn color is that of the ginkgo, Ginkgo biloba. Some know it at the maidenhair tree. Except for older trees that produce messy and stinky fruit, it is a notably clean tree. Perhaps it is too clean. It drops nothing all year, but can defoliate too soon once it develops it striking autumn color. Minimal chill actually prolongs the process.
Ginkgo is dioecious, with separate genders. Modern cultivars for landscapes are male, so produce no obnoxious fruit. Female cultivars that produce nuts and fruits are not commonly available in nurseries locally. (As objectionable as their aroma is, the nuts and fruits are edible.) Some people may be allergic to the pollen of mature male trees. Many mature trees predate modern cultivars.
Trees are somewhat slender and perhaps sparse while young. They develop a broader canopy as they age. Trees can get more than 50 feet tall, with sculpturally irregular branch structure. Foliar venation radiates outward from the petioles. Leaves, which are about two or three inches long, therefore have the shape of fishtails. Leaves on current season stems are cloven into paired lobes.
Horticulturist Tony Tomeo can be contacted at tonytomeo.com.