Trees to Try
02 Sep 2010
Autumn is tree-planting time, so dig a hole for these favorites of the senior curator at Denver Botanic Gardens. They’re tough, generally xeric and pretty to boot.
Text and photos by Panayoti Kelaidis Trees and shrubs are the bones of our gardens, the structure upon which everything depends. We often ignore them in summer, when the rush of flowers and vegetables clamors for our attention. But as the days cool, fall colors stain the canopies and by October, our gardens are ablaze in autumn splendor. As senior curator at Denver Botanic Gardens, I’m blessed with the task of monitoring hundreds of trees and shrubs as they attain splendor. Here are my picks for trees and shrubs that thrive in tough conditions, and add interest and color to the landscape.Black Maple (Acer nigrum)
Coloradans struggle with sugar maples. But imagine a maple with the same stunning fall color as a sugar maple that thrives in our alkaline soils and takes our changing seasons with equanimity. That is precisely what black maple does. This picture shows an astonishing specimen I’ve admired for decades on Colorado Boulevard in Denver that is surely the state champion. It’s nearly 80 feet tall and almost as broad, with a vigorous constitution. It turns color late, often in late October and November, with the same melting orange and pink tones as the sugar maples of the northeast. But what a toughie this one is!
Garden tip: This can grow into a massive street tree—even larger than the numbers cited below—if well sited. Plant it where it has plenty of room. Height: 50 feet Width: 45 feet Culture: Occasional deep watering. A loamy or sandy soil is best.
Redbud (Cercis canadensis)
Redbud invariably produces a huge display of bright magenta flowers in April and May. As you drive around older neighborhoods, massive redbuds are surprisingly common. Although this eastern woodlander is reputed to be temperamental, if you can obtain northern stock it seems to be one of the tougher garden trees. I’m amazed to see it growing in some very exposed, even hot spots. And I know, once established, it can be very drought tolerant. This isn’t surprising, considering that both the California and Mediterranean redbuds can endure half a year without rain.
Garden tip: There is a place for a redbud in every Front Range garden. Surprisingly fast growing and endlessly rewarding. Height: 20 feet Width: 15 feet Culture: Thrives in a surprising range of soils and exposures, provided you have a cold-hardy strain.
Carol Mackie Daphne (Daphne x burkwoodii ‘Carol Mackie’)
Daphnes are taproot shrubs, and best planted young. But everyone wants huge specimens, and some are willing to pay for them. Alas, a great proportion of the larger planted daphnes die, so this shrub has an aura of difficulty it doesn’t deserve. Buy daphnes young; they will grow quite quickly and soon you’ll have them coming out your ears!
Garden tip: Do not let daphnes dry out too deeply or get too wet. The other culprit is too much nitrogen fertilizer—DON’T do it. Our soils are rich enough for daphnes, which can live a very long time in well-drained sites in part sun. Height: 4 feet Width: 4 feet Culture: Loamy soil is best, with occasional deep watering.
William Baffin Rose (Rosa ‘William Baffin’)
It’s been several decades since the first Canadian roses invaded Front Range gardens. As far as I’m concerned, they can conquer the entire state! The wonderful shrub roses bred at the Morden Research Station and elsewhere in Canada are famous for blooming repeatedly in summer, and having far greater hardiness and grace than the roses we used to grow. Few are more magnificent than the giant William Baffin rose, which can be trained to climb and continuously produces huge pink flowers for months on end. This gorgeous rosebush deserves a spot in every large garden.
Garden tip: This is a monster of a plant, so give it lots of room to grow. Very tough and adaptable, if you have space. Height: 10 feet Width: 12 feet Culture: Full sun is best, on good loam or sandy loam. Occasional deep watering.
Goldenrain Tree (Koelreuteria paniculata)
Surely goldenrain tree is one of the most glorious trees. Its spectacular yellow flowers transform into impressive, lantern-shaped seedpods in fall. This compact Chinese gem is best grown in hot exposures, particularly xeriscapes and on the south side of buildings, where its steely constitution demonstrates its steppe ancestry. Too much water or shade makes the branches grow too quickly and become brittle and susceptible to breakage in heavy snows, especially when the leaves are still on the tree. When the tree’s yellow flowers fall in August, they literally rain. Then the golden leaves rain and finally the seedpods—a true surfeit of golden rain!
Garden tip: This tree can self-sow a lot in areas mulched with wood chips and watered excessively. Seedlings are easily pulled up, however. Plant it on hot, exposed spots, abuse it a bit and it will be happy. Height: 40 feet Width: 30 feet Culture: Best in full sun. Tolerates considerable drought, once established. Very tolerant of a wide range of soils.
Lacebark Pine (Pinus bungeana)
I fondly remember hearing the late CU professor Paul Maslin describe these hoary trees he grew up with in China. Eventually I went to China myself and saw massive specimens with white trunks at monasteries in the north of the country. But it’s the younger plants that sport the fabulous lacy bark that gives this plant its name. As the tree ages, the bark turns a glistening white.
Garden tip: This tree seems to thrive wherever I have seen it planted. Full sun, however, is best. Height: 45 feet Width: 20 feet Culture: Occasional deep soaking. A sandy or loamy soil is best.
Rocky Mountain Mountain Ash (Sorbus scopulina)
Garden tip: This tree does not like it too hot or too dry. Otherwise, it promises to be a superb small tree that would fit in almost any Colorado garden at any elevation. Height: 25 feet Width: 15 feet Culture: Sun or part shade, and loamy soil. Occasional deep watering.I am always mystified that anything as gorgeous as European mountain ash (Sorbus aucuparia) is not that frequently planted, and that our own native mountain ash is essentially nonexistent in gardens here. Both turn spectacular colors in fall, from yellowish-gold to flaming orange. I’ve noticed that birds always devour the berries of our native mountain ash in autumn, but berries on the European mountain ash persist until spring. Why is that, I wonder?
Golden Yellowhorn (Xanthoceras sorbifolium)
This rather unusual tree from north-central China loves to grow in Colorado. Plant Select has selected and promoted it, and yet I still only know of a handful of these in gardens. In April it’s covered with enchanting white flowers with a yellow center that turns deep red once fertilized. The flowers gradually transform into huge seedpods that remind me of Christmas ornaments full of black, marble-sized seeds. If you want to confound garden visitors, plant this gem of a plant, which is decorative in all seasons.
Garden tip: Not too wet or shady. It seems to do well in most places I’ve seen it planted. A very unusual and rare tree in Colorado. Height: 25 feet Width: 15 feet Culture: Full sun and sandy or loamy soils. Very drought tolerant, once established. Deep watering is recommended in drought years.
Panayoti Kelaidis is a plant aficionado, and senior curator and director of outreach at Denver Botanic Gardens. 
