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Some new favorite trees
From the Davis Enterprise, June 25, 2009
Some of my new favorite trees
A few years ago I wrote
a column about some of my favorite trees
: species and varieties that I recommend frequently, that have good habits, some seasonal beauty, reasonably carefree, and suitable to a range of garden situations.
Quick picks
Ginkgo biloba
Maidenhair tree
Pistacia chinensis
Chinese pistache
Platanus hybrids
Sycamore
Liriodendron
Tulip tree (not Magnolia)
I still stand by most of the trees on that list: Chinese pistache, Littleleaf linden, male varieties of Ginkgo biloba; hybrid maples, oaks, sycamores and plane trees (
Platanus
), tulip tree (
Liriodendron
), and Zelkova. New pest problems, new varieties, and more years of observation have led me to modify my list somewhat.
Poor availability would take
Koelreuteria elegans
off that list (check the Arboretum sale in the fall). Crape myrtles and plums are still among the most popular small choices, and I suggest considering disease-resistant crabapples (
Malus
) for another option in small flowering trees.
Such lists are very subjective. There were comments that I didn't include enough native species, to which I reply that there frankly aren't that many native tree species that are suited to the average garden. Our native Valley oak (
Quercus lobata
) is a wonderful tree in its place, but the shade is light and the growth rate is slower than many people want. Other native species such as Fremont cottonwood and California black walnut aren't appropriate for many situations. However, there are some new choices among native trees from California and the southwest.
Updated recommendations
Things change, even in the world of trees. In 2002 a pest arrived in the Sacramento Valley that attacks Chinese hackberry (
Celtis sinensis
), so that species is off my list. Calleryana pears have almost entirely fallen out of favor due to poor branch structure, especially in older varieties such as Bradford. On the other hand, new varieties of other trees have come into the trade that have better disease resistance: Columbia plane tree and Roberts sycamore, both in the genus
Platanus
, resist anthracnose disease (and mildew in the case of Columbia). Roberts is a form of the California native sycamore, a species we had difficulty recommending in the past due to the spring leaf blight. Bolder leaves and brighter white trunk have always made the California sycamore one of the prettier members of
Platanus
, so it's good to have a disease resistant form.
Where do new trees come from?
How, you may ask, do growers come up with these tree varieties? Most often they are selections, which are then clonally propagated.
Roberts sycamore is an example: somebody, looking at a stand of seedling-grown trees, observed one that was more robust, had bigger leaves, and appeared to be free of disease compared to the others. So he or she named it and propagated it by cuttings or by grafting onto a rootstock.
The advantage of this is that you get a tree with known characteristics, better in some specific way than those grown from seed. For example, Keith Davey is a male variety of Chinese pistache has reliable bright red fall color; Chinese pistache trees grown from seed vary from yellow to red to purple, and half of the seedlings are female. You want male (no berries), you want red: buy Keith Davey. The drawback, if a variety comes to dominate the trade, is that some undesirable characteristic may become evident with age. Once Bradford pears began falling apart all over the country, about 20 - 30 years after they were widely sold, the problems with branch structure of that variety became painfully obvious. Fortunately, such duds are less common than the successes.
Evergreens
The cultivars of coast redwood (
Sequoia sempervirens
) that we grow (Soquel, Aptos Blue, etc.) are selections. The names arise from the region in which these individual parent trees, deemed superior by an observant horticulturist, were found. Somewhere in the city of Soquel is the parent of all
Sequoia sempervirens
'Soquel' trees: all that you buy and plant are clones of that original tree.
Libocedrus (Calocedrus) decurrens
-- Incense cedar
Fond as I am of redwoods, I do think they get too large for many yards. The density that we prize for privacy can make a shady challenge after twenty years or so. A conifer that I've come to appreciate more over the years is our native Incense cedar (
Libocedrus decurrens
). At 2 - 3' a year, it grows more slowly than redwood. The habit is more open, which reduces its value for screening but may make it a better garden companion as it ages. Eventually Incense cedar gets very large, but much more slowly than does Coast redwood. And it is much, much more drought tolerant.
A smaller broad-leaved evergreen that is easy to recommend is
Arbutus
'Marina': if you like madrone (
Arbutus menziesii
), plant this instead. It has the same mahogany-colored bark, but is tolerant of garden conditions (madrone nearly always dies when planted outside its native range). It has pretty flowers in winter, attractive orange fruit in fall and winter enjoyed by the birds. Marina grows slowly, to about 15 feet in 5 - 10 years; ultimately much larger, but easily kept smaller with pruning every few years.
Choosing among Crape myrtles
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Crape myrtles (
Lagerstroemia
) are mostly grown as small patio-size trees with showy flowers. Mildew resistance has been an improvement in varieties introduced over the last few decades. Some new forms have much more intense flower color, and a couple are noteworthy for size and vigor.
Unlike selected varieties described above, new crape myrtles are the result of intentional breeding programs where seedlings are grown, assessed, and winnowed down as improvements appear in successive generations.
Breeding trees requires lots of space, meticulous record-keeping, and considerable patience!
Dr. Carl Whitcomb grew over 160,000 seedlings over 14 years before he introduced a spectacular red variety that has become very popular. It began as a selection: seedlings were grown from a particularly nice tree in Oklahoma. Then began the process of selecting the best seedlings, chosen for leaf color and disease resistance, and throwing out the rest. Their seeds were planted, and grown out until they bloomed (which takes a couple of years). Breeders have to be pretty ruthless, as they are reviewing thousands of seedlings. Eventually he came across a strong-colored seedling and commented in his notes that this one is "dynamite." Hence the name: that vivid red Crape myrtle you're seeing in landscapes is a patented plant with the trademarked name Dynamite.
Lagerstroemia indica 'Dynamite' showing variable bloom color
A note about this intense red Crape myrtle: flecks of white will appear in the blossoms after periods of cooler weather, affecting blossoms that set while we are having spells of cool delta breezes here. Some buds that develop under cooler conditions also open more pink than red (see photo). While these changes diminish the overall intensity of the bloom, they lend some interest to the blossoms up close. It is unavoidable and harmless.
Crape myrtles as shade trees
Dr. Whitcomb was breeding within the species
Lagerstroemia indica
. At the U.S. Arboretum, meanwhile, a long-term breeding program
between
species began in 1964, as
L. indica
was crossed with a mildew-free species (
L. fauriei
) that had been imported from Japan in 1956.
Lagerstroemia x 'Muskogee'
That breeding program has resulted in some of our best Crape myrtles, and in my opinion the most outstanding is Natchez. Most crape myrtles are small to medium trees grown primarily for the flowers. This white-flowered variety can grow 5' a year to 30' with equal spread! Great fall color, with beautiful cinnamon brown bark, Natchez is really a shade tree that happens to have nice flowers. Another large variety is Muskogee, which has soft pink flowers with a touch of lavender. Both have huge clusters of flowers, a nice round habit, and grow fast enough to provide shade quickly.
Lagerstroemia x 'Muskogee'
More recommendations.
There have always been trees that I would recommend but for limited availability. Desert willow (
Chilopsis linearis
) has long been a personal favorite, but was never really in the nursery trade. I got mine at a native plant sale many years ago, and it has grown to about 30 feet tall with about half that spread.
Chilopsis linearis
-- Desert willow
Desert willow isn't a willow at all; the name refers to the narrow, loosely hanging foliage. It's actually in the trumpet vine family (Bignoniaceae), and sports pretty pink tubular blossoms all summer. Hummingbirds love all members of this family, and my tree is active with hummers throughout the bloom season. Native to the southwestern deserts, Chilopsis is very drought tolerant. It provides a light shade due to the open growth habit, making it easy to garden under.
On my previous list I mentioned a couple of small trees, including the ubiquitous redleaf plum. Now we have another option with the same intense burgundy foliage: purple smoke tree
(
Cotinus coggygria
)
has become readily available over the last few years. Most growers produce either the seedling selection Purpureus (aka Atropurpurea) or the clonal selection Royal Purple. The name refers to the feathery appearance of the seed structures after the bloom. Smoke tree is a slow grower, suitable as a shrub or small tree and is very drought tolerant.
The
original article
was in 2002, so I'll update again in 2016. Stay tuned!
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© 2009 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
www.redwoodbarn.com
Feel free to copy and distribute this article with attribution to this author.
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