The Seed is the horticultural magazine of the Nebraska Statewide Arboretum. It is published twice a year for the members of the Arboretum. This issue was written by Karma Larsen. Copyright 1999. For a full version of this publication with visuals, photographs, charts, landscape designs, etc. call 402-472-2971.

The Seed, Spring 1999

Flowering Trees

"If you want to create a garden for a year, then fill the borders with flowers. But if you want to create a garden for a lifetime, then plant it with trees and shrubs." John Kelly

     In just a few weeks, twigs now invisible against the winter background will suddenly fill their expanse with as much color and bloom as a good-sized flowerbed. We barely notice them now, but their day is coming.
      In Nebraska, winter forces a certain amount of patience (and simultaneously impatience) on us. If the vegetable gardener's hope and desire is for that first tomato, the flower-lovers among us wait as anxiously for the first blossoms. And one of the quickest, easiest and longest-lasting routes to early color is to plant spring-flowering trees and shrubs.
      It's hard to think of a garden with no trees. Frank Church says "In the intimate and humanized landscape, trees become the greatest single element linking us visually and emotionally with our surroundings. Other manifestations of nature–great rocks, deserts, moors, torrents, hurricanes–stir us, fill us with awe, make us afraid or humble, but a tree we understand and can allow to become part of us. It's no wonder that when we first think of a garden we think of a tree."
      To a large extent trees can determine the climate of the yard, certainly the microclimate of the area directly around them. They provide shade and protection from wind, they act as walls and ceilings to enclose outdoor "rooms." They provide interest of many kinds, appealing to all the senses by their fragrance, fruit, texture, even sound. Perhaps best of all, they are constantly changing. From buds to foliage to bark, they're a continuously visible but changing part of the landscape.
      We use them to frame some views, block out others. More often than not, the trees themselves are the focal point–whether they're being seen from the yard or from inside the house. Wildlife depend on them for food and shelter and add further interest.
      Our desires for maximum efficiency make us think in terms of seasonal interest, wanting "returns" for as much of the year as possible. And in fact, spring-flowering trees are rarely one-stop shows. Their blossoms often give way to fruit or colorful foliage later in the year, and many of them also have unusual and attractive bark.
      Most spring-flowering trees are good understory trees, thriving in the protection of the canopy provided by larger trees. The pale colors of their blossoms can be especially noticeable in the foreground of large evergreens. And the mulched area under these small trees can be a good place to plant spring bulbs.
      For a brief overview of spring-flowering trees, the chart at the end of this issue lists some of the things you may want to take into account in selecting trees for your landscape: mature size, bloom time, color and exposure.
      In the meantime, look out at your landscape and imagine what it might look like in future springs if you planted…

Redbuds
      Eastern redbud, Cercis canadensis, is a good landscape selection, doing well on its own, under the canopy of larger trees or in a grouping of small trees. It provides some of the earliest blossoms, opening its purplish pink flowers in late March or April. The cultivars ‘Alba' and ‘Royal White' have white flowers.
      Since they bloom so early, redbud's flowers almost seem to emerge from the bark. And even 4-year-old trees can produce blossoms. Redbuds have an extensive range and not all strains are cold-tolerant, so if you're planning to buy one, check to make sure it was grown from locally selected seed.

Magnolias
      Two of the magnolia species adapted to Nebraska are saucer magnolia, Magnolia x soulangiana and Loebner magnolia, Magnolia x loebneri.
      Choosing the right site is critical for magnolias. The temptation is to place them in a protected location, but if it's a warm south location, they may bloom earlier than usual and be even more susceptible to a spring freeze. Dirr writes that, for Magnolia soulangiana, "1(2) out of every 3 or 4 years would be a conservative estimate for almost total flower loss in many areas." Writing this on a February day with a temperature of 60°, those odds don't sound at all pessimistic. Still, the blossoms they produce are worth some risk.

Hawthorns
      The hawthorns are widely used in landscape plans, often close to buildings to provide horizontal lines and human scale to large buildings. They provide excellent year-round interest–spring flowers, glossy green summer foliage, beautiful fall color and fruit that persists through winter. And they can tolerate hot, dry conditions. The drawback is that they can be susceptible to many diseases and insects: fireblight, leaf blight, at least nine species of rusts, mildews, aphids, borers, miners, mites, to name just a few.
      The blossoms of Crataegus x mordenensis open in May and its deep red fruits ripen in September and persist into late fall. Cockspur and Washington hawthorn, Crataegus crusgallii and C. phaenopyrum, have 2" thorns, making them a questionable choice for high-traffic or play areas, but there are thornless varieties available. The fruits of green hawthorn, Crataegus viridis, are a deep red and often remain through winter; and this cultivar is somewhat less susceptible to rust than other hawthorns.

Crabapples
      There are endless varieties of flowering crabapples, and in full flower, few flowering trees can compete with them. But they are susceptible to a number of diseases. In western Nebraska, fire blight is the predominant disease. It can eventually kill the trees, unlike scab and cedar-apple rust that plague the central and eastern parts of the state, but primarily damage only the appearance.
      Don Steinegger, UNL horticulturist, recommends planting disease-resistant varieties but warns that disease-resistance is not a permanent characteristic since the fungi and bacteria they are susceptible to are continually changing. Some of the cultivars he recommends (see NebGuide Crabapples for Nebraska Landscapes for a complete listing) are: ‘Zumi Calocarpa' for flower display and abundant tiny red fruit; ‘Molten Lava' and ‘Red Jade' for horizontal branching habit; ‘Professor Sprenger' for persistent fruit; and ‘Dolgo' for harvesting the fruit.
      Since there are so many varieties with such varied periods of blooming, it is possible to plant trees that can extend flowering time from April all the way through July. There are also some varieties that hold their fruit well into the winter, adding winter color and providing food for birds. The two crabapple varieties gardening columnist Lauren Springer chose, ‘Ormiston Roy' and ‘Adams', produce fruit that persists long into the winter but she believes "that has more to do with the local birds' palate than with climate or the tree's physiological state." (She also gives some credit to the close supervision of her nine cats.) One of the crabapples at UNL's East Campus, Malus ‘Donald Wyman' was still holding fruit early in February.

Others to Try
      Fringetrees will survive in almost any landscape setting. White fringetree, Chionanthus virginicus, an American native, bears small white "clouds of bloom" in the spring. Chinese fringetree, Chionanthus retusus, blooms slightly later in spring, has smaller blossoms of a purer white, and its leaves are shinier and more leathery. Michael Dirr says he would "like to make a case for this as the national shrub for even dogwood does not carry itself with such refinement, dignity and class when in flower."
      Yellowhorn, Xanthoceras sorbifolium, is similar to fringetree but is not widely used. Like fringetree, it has white and yellow clusters of flowers in late spring and tolerates a wide variety of soils. Yellowhorn, however, requires full sun.
      Dirr believes American smoketree, Cotinus obovatus, "may be the best of all American shrub trees for intensity of color." The yellow flowers it produces in June are followed by a much more dramatic show as the dense hairs on the flower clusters go through several color changes, eventually turning a smoky pink beginning in June and continuing into August. The foliage goes from blue-green in spring to magnificent yellow, orange, and deep purplish red in the fall, sometimes with all colors present at the same time.
      Shantung maple, Acer truncatum, also has excellent fall color, turning yellow-orange and red in the fall. Its bright yellow flowers appear in April before the foliage is visible. It is tolerant of almost any of the difficulties associated with street plantings, i.e. poor soil, heat and drought.
      Amur maackia, Maackia amurensis, is valued not so much for its flowers as for its beautiful amber-colored bark. It is a very hardy tree and is good for lawn and patio use. New foliage is grayish, giving way to a dark green and bearing white blossoms in June or July. It is plagued by few diseases or pests, and even does well in planters.

Serviceberry
      Serviceberry, Amelanchier x grandiflora, also known as Juneberry, straddles the line between a small tree and large shrub. Regardless, its white blossoms, attractive fruit and good fall color make this an outstanding landscape plant, resulting in its selection as 1998 "Tree of the Year" for Nebraska. The cultivars ‘Autumn Brilliance' and ‘Robin Hill' are recommended.

Dogwoods
      While the well-known flowering dogwood (Cornus florida) of the southern United States is very difficult to grow in Nebraska, several other beautiful dogwoods can be successfully grown. The tree selected by members of the Nebraska Nursery and Landscape Association as "Tree of the Year" for 2000 is Pagoda dogwood, Cornus alternifolia. Its yellowish white flowers open in May or early June. It prefers partially shaded locations, and moist, acid, well-drained soil. As in the selection of cold-resistant redbuds, it's best to find a northern seed source, if possible. Its branches, which open out in tiers, create very strong, horizontal lines.
      Cornus kousa is somewhat better adapted to our soils than Cornus florida, but it still prefers moist, acid, well-drained conditions. Cornus mas can tolerate acidic soils, high pH or even clay soils. Its yellow flowers open in March, often before anything else. ‘Golden Glory' is a cultivar that has reliably produced an abundance of flowers. Dirr says it is "the longest lived of all Cornus species" in the Midwest.
      Callery pear, Pyrus calleryana, is tolerant of heat, drought and compacted soils. The cultivar ‘Bradford' has been widely used in urban settings over the last decade or so, but its tight branching habit can cause it to split in snow and ice storms. Some of the other cultivars are less likely to split with age, among them ‘Aristocrat' and ‘Chanticleer'.
      European birdcherry, Prunus padus, can grow to 30-40', bears white blossoms in early May. ‘Plena's' flowers are large and double, and last longer than those of most cultivars. Prunus sargentii is slightly smaller, 20-30' high, with pink blossoms in early May and shiny, dark green foliage in summer that turns bronze-red in the fall. The blossoms of Prunus virginiana, common chokecherry, are white and open in late April.

Lilacs
      Lilacs are synonymous with spring in Nebraska. While the most familiar lilacs are shrubs, one tree-like species also deserves a place in the landscape. The blossoms of the Japanese tree lilac, Syringa reticulata, are white, unlike bush varieties. It is extremely adaptable to difficult sites and also resistant to mildew, scale and borers. Dirr says it is one of the toughest and "possibly the most trouble-free lilac." The cultivars he recommends are ‘Ivory Silk', ‘Regent' and ‘Summer Snow' for their flower production, uniform habit and foliage.

Viburnums
      The viburnums are also known mainly as shrubs, but have several species that take on tree-like proportions. "A garden without a viburnum is akin to life without music and art" is Dirr's introduction to this family of shrubs. Some of the notable spring-flowering varieties are nannyberry and blackhaw viburnum, Viburnum lentago and prunifolium.
      The 1" long buds of the nannyberry viburnum open to 3-4 _" white inflorescences in May. This shrub/small tree can grow to a 30' height with a variable spread. It is susceptible to mildew and so even though it grows well in shade, it should be planted where there is good air movement around it.
      Blackhaw viburnum has similar blossoms, grows to a 20' height and is less susceptible to rust. Both have good fall color, with foliage going to a purplish red.

"Now!"
      If you simply can't wait any longer, you can force branches of any of the trees mentioned in this issue. Choose branches with lots of plump flower buds, cutting 6-18" branches just above a side bud so you don't leave a stub. If temperatures are below freezing, submerge them overnight in room temperature water. Cutting a 2" vertical slit in the bottom of the stem helps them absorb water, which should be changed every few days. Place them in a cool, humid room out of direct sunlight. It will take 1-8 weeks, depending on how far along the buds were.
      But hopefully by the time you read this, the "march of buds" Karel Capek writes about in The Gardener's Year will have begun, starting with the forsythias while "the other bushes and trees are still waiting for some imperative ‘Now!' which will breathe from the earth or from the sky; in that moment all buds will open, and it will be here."