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Captivating Conifers for the Landscape

American Nurseryman
February 15, 2008

Text and photos by Richard and Susan Eyre

Landscaping and garden design is a fantastic career choice. Nurserymen, landscape architects, designers and contractors are people who express their art in the gardens and landscapes they create for their clients. Legacies of living art are created for future generations to admire when you choose a captivating conifer for the landscape or garden. Every modern landscape can be enhanced with the use of conifers as foundation plantings or as barriers to negative lines of sight. The diverse attributes of conifers enable them to provide four seasons of interest as the "bones" in the American mixed perennial border.

Site plants on an inclined plane or irregular rolling slope. Slope adds interest to a flat surface and provides the opportunity to stage dwarf plants toward the foreground. The design should capture the positive viewing lines of the property. Large or intermediate conifers can be used to block unwanted sightlines. Dwarf garden conifers provide a wide range of forms to add to the landscape.

Once some of the larger design concepts are identified, it is important to look at each conifer individually since each one offers a unique form. Color, texture, seasonal changes and cones provide great options. Whatever landscape situation exists, there is a superlative conifer available for that site. Basic knowledge of conifers and of the site is required to make wise plant choices. With the wide palette of conifers available, there are plenty of appropriate choices. Therefore, why keep using some of the older conifer cultivars that are prone to inherent disease problems?

Before planting conifers, you must be able to answer three critical questions:

The American Conifer Society, Lewisville, NC, has adopted four size categories for conifers: miniature, dwarf, intermediate and large. The letters (M), (D), (I) and (L) are used in the following descriptions to best depict the mature size category for each cultivar (see table below). Note the size of the internode to determine the growth rate. The internode indicates the rate of growth for one year from the terminal bud to the first set of branchlets called a whorl. Size may vary due to cultural, climatic and regional factors.

The American Conifer Society’s tree growth sizes
Category Growth per year Size at 10 years
Miniature (M) Less than 1 inch 1 foot
Dwarf (D) 1 to 6 inches 1 to 6 feet
Intermediate (I) 6 to 12 inches 6 to 15 feet
Large (L) More than 12 inches More than 15 feet

Conifer planting considerations. The first critical consideration is to determine the drainage and percolation of the site. Most conifers thrive in well-drained, sandy, clay loam soil in full sun. Not all projects have ideal conditions, but good drainage is essential to guarantee the success of most plantings.

Many contractors are landscaping houses in new subdivisions, which is like trying to landscape a strip mine. All the good topsoil has been removed and replaced with only a few inches of topsoil. Hard clay soil and bad drainage remains. Landscape plants need help where bad drainage is concerned. Test your soil percolation by digging a 2-foot-deep hole with a posthole digger. Fill the hole with water, let it drain, and fill it again. If the hole does not drain in two hours after the second filling, the soil is limited for conifers. In heavy clay, raise half the root ball out of the clay layer and surround the protruding half with good topsoil. Another solution is to remove narrow channels of clay leading away from the plant, like spokes of a wheel. Replace that soil with sand or pea gravel so water and rootlets have an easy path. Water must drain away easily, or the roots will rot due to lack of oxygen.

If your soil is heavy, wet and can't be amended, there are some conifers that are naturally predisposed to such conditions. Choose a deciduous conifer, such as Larix (larch), Taxodium (bald cypress), Metasequoia (dawn redwood) or Thuja (arborvitae). Taxodium distichum (bald cypress) is one of the most versatile conifers because it can thrive in standing water or on a dry, rocky ridge and is the most adaptable to heavy clay soils in new subdivisions. Taxus (yew), Pinus (pine), Picea (spruce) and Abies (fir) demand good drainage and will die with too much water in the soil.

The second critical consideration for conifers is the amount of sun your site receives in the summer. Most conifers want to live in full sun. There is a wide variation in conifers as to their shade tolerance. Only a few species will tolerate and thrive in partial shade. Some conifers that tolerate shade are arborvitae, yew and Tsuga (hemlock). There are many cultivars of hemlocks with a variety of forms, colors and textures to make a more interesting shade garden.

Dwarf forms of Tsuga canadensis (Canadian hemlock) include 'Bennett' (D), 'Jeddeloh' (D), 'Jervis' (D), 'Gentsch White' (D) and 'Albospica' (D). Intermediate forms of Canadian hemlock include 'Dawsoniana' (I), 'Geneva' (I) and 'Pendula' (I). Tsuga diversifolia (Japanese hemlock) and Tsuga caroliniana (Carolina hemlock) are great alternatives to Canadian hemlock.

If your site receives some shade, but at least four to five hours of direct sun each day in the summer, then use Pseudotsuga menziesii (Douglas fir), Abies balsamea (balsam fir), Pinus cembra (Swiss stone pine), Pinus strobus (eastern white pine) or Picea abies (Norway spruce). Sun-loving conifers planted in the shade may live, but do not thrive or grow properly.

Recommended dwarf cultivars are Pseudotsuga menziesii 'Fletcheri' ('Fletcheri' Douglas fir; D), Abies balsamea 'Nana' ('Nana' dwarf balsam fir; D), Pinus cembra 'Glauca' ('Glauca' Swiss stone pine; D), Chamaecyparis obtusa 'Nana Gracilis' ('Nana Gracilis' hinoki cypress; D) and Japanese hemlock (D). The thick needles of Sciadopitys verticillata (umbrella pine; D) add tremendous texture to landscapes with a northern or eastern exposure.

The third consideration for selecting conifers is the rate of growth of the desired plant. The contractor must know about the growth rates to aid in proper selection and siting of the plants. It is disappointing to see fast-growing trees planted too close to buildings and each other. Overplanted landscapes look great for a few years, but then the nightmare begins. Like baby raccoons, conifers are cute when they are small, but can quickly grow into nuisances. By using slower-growing dwarf conifers, the growth rate is cut in half and doubles the life of the planting before the plants outgrow the available space. Spacing plants properly is essential. Using slower-growing plants can extend the life of a landscape by 10 to 12 years.

Many landscapers are daunted by the sheer number and diversity of conifers and are unsure how to use them. Many tend to use the same common evergreens in every landscape situation. Professionals are encouraged to do more than plant a straight row of one conifer species as a hedge or fence line. Large-scale conifers are the most useful plant for screening or windbreaks, and they are far more interesting when planted in irregular triangles using more ornamental or slower-growing forms in the foreground.

Conifer forms. Dwarf conifers provide a wide range of forms to add to the landscape. Fastigiate or columnar trees add height to a garden, but leave a narrow footprint in the landscape. Picea pungens 'Fastigiata' ('Fastigiata' Colorado spruce; L), Picea abies 'Cupressina' ('Cupressina' Norway spruce; L), P.abies 'Hillside Upright' ('Hillside Upright' Norway spruce; I) and Pinus strobus 'Fastigiata' ('Fastigiata' eastern white pine; L) are selections hardy to Zone 3, and they like full sun.

Other upright, narrow forms of conifers include Pinus sylvestris 'Fastigiata' ('Fastigiata' Scots pine; I), P.sylvestris 'Spaan's Fastigiate' ('Spaan's Fastigiate' Scots pine; I), P.sylvestris 'Sentinel' ('Sentinel' Scots pine; L), Thuja occidentalis 'DeGroot's Spire' ('DeGroot's Spire' arborvitae; D), T.occidentalis 'Emerald' ('Emerald' arborvitae; I), T.occidentalis 'Malonyana' ('Malonyana' arborvitae; I), Juniperus communis 'Gold Cone' ('Gold Cone' common juniper; D), J.communis 'Suecia Nana' ('Suecia Nana'common juniper; M), J.communis 'Compressa' ('Compressa' common juniper; M), Picea glauca 'Pendula' ('Pendula' white spruce; I) and Pinus cembra 'Glauca' ('Glauca' Swiss stone pine; I).

Picea omorika 'Pendula' ('Pendula' Serbian spruce; L) remains narrow in form, with branch tips that have blue undersides pointing up. Chamaecyparis nootkatensis 'Green Arrow' ('Green Arrow' false cypress; L) and C.nootkatensis 'Van den Akker' ('Van den Akker' false cypress; L) add drama to any landscape. Taxus×media 'Stovepipe' (D) or Taxus×media 'Pilaris' (D) are great for small spaces in the shade. Pinus leucodermis 'Emerald Arrow' ('Emerald Arrow' Bosnian pine; I) is salt-tolerant with stiff, green needles.

Dwarf conifers. Dwarf and miniature conifers are ideal as foundation plants because they require low maintenance and are highly ornamental. Once established, these forms do not need pruning or fertilizing. Good pyramidal forms are blue Picea pungens 'Montgomery' ('Montgomery' Colorado spruce; D), green Picea abies 'Clanbrassiliana Stricta' ('Clanbrassiliana Stricta' Norway spruce; D), P.abies 'Asselyn Compacta' ('Asselyn Compacta' Norway spruce; D) or P.abies 'Mucronata' ('Mucronata' Norway spruce; I). Recommended low, green spreaders are Picea abies 'Pumila' ('Pumila' Norway spruce; D), P.abies 'Repens' ('Repens' Norway spruce; D) or P.abies 'Elegans' ('Elegans' Norway spruce; D).

Slow-growing, globose conifers include Pinus strobus 'Blue Shag' ('Blue Shag' eastern white pine; D), P.strobus 'Horsford' ('Horsford' eastern white pine; D), P.strobus 'Nana' ('Nana' eastern white pine; D), Picea pungens 'Thuem' ('Thuem' Colorado spruce; D) or P.pungens 'Glauca Globosa' ('Glauca Globosa' Colorado spruce; D). Picea omorika 'Nana' ('Nana' Serbian spruce; D) offers a globose shape with an attractive bicolor needle (green on top with a blue underside).

Mounding and spreading conifers. Dramatic, mounding, conifer forms include Pinus×'Jane Kluis' (Pinus densiflora and Pinus nigra hybrid; D), Pinus densiflora 'Low Glow' ('Low Glow' Japanese red pine; D) and Pinus nigra 'Hornibrookiana' ('Hornibrookiana' Austrian pine; D) with its outstanding white buds. Dwarfs Pinus mugo 'Valley Cushion' ('Valley Cushion' mountain pine; D) and P.mugo 'Slowmound' ('Slowmound' mountain pine; D) may grow 1 to 3 inches or less per year during the first 10 years of their lives.

Spreading conifers make great groundcovers, such as yellow Juniperus horizontalis 'Mother Lode' ('Mother Lode' creeping juniper; D), yellow and green Juniperus×pfitzeriana 'Daub's Frosted' ('Daub's Frosted' spreading juniper; D), green Juniperus sabina 'Calgary Carpet' ('Calgary Carpet' savin juniper; D), green Juniperus communis 'Green Carpet' ('Green Carpet' common juniper; D), green Pinus sylvestris 'Albyn' ('Albyn' Scots pine; D), light green P.sylvestris 'Hillside Creeper' ('Hillside Creeper' Scots pine; D) and bicolor Pinus pumila 'Blue Dwarf' ('Blue Dwarf' dwarf Siberian pine; D).

Dramatic-looking conifers. Large pyramidal forms, pendulous forms, pruned or poodled conifers add high drama to larger spaces. Any weeping tree will attain the height you want by staking. After the desired height is reached, all growth is usually downward. A pendulous tree that is never staked becomes a groundcover, such as Picea abies'Pendula' ('Pendula' Norway spruce; I).

Other dramatic specimen trees are Chamaecyparis nootkatensis 'Glauca Pendula' ('Glauca Pendula' Alaskan false cypress; L), Larix decidua 'Varied Directions' ('Varied Directions' European larch; I), Pinus strobus 'Pendula' ('Pendula' eastern white pine; I), Picea pungens 'Glauca Prostrata' ('Glauca Prostrata' Colorado spruce; D) and P.pungens 'Glauca Pendula' ('Glauca Pendula' Colorado spruce; I). For shadier sites, Pseudotsuga menziesii 'Graceful Grace' ('Graceful Grace' Douglas fir; I) and Tsuga canadensis 'Pendula' ('Pendula' eastern hemlock; I) are outstanding.

Many garden conifers display a rainbow of colors in shades of green, yellow, blue, orange and purple. Yellow cultivars can add color to a garden or landscape, but they generally need full sun to maintain great color. The thread leaf Chamaecyparis pisifera 'Golden Mop' ('Golden Mop' sawara false cypress; D), C.pisifera 'Filifera Aurea Nana' ('Filifera Aurea Nana' sawara false cypress; D) and C.pisifera 'Lemon Thread' ('Lemon Thread' sawara false cypress; D) add a gold or yellow accent, plus interesting texture. Thuja occidentalis 'Sunkist' ('Sunkist' arborvitae; I) and T.occidentalis 'Yellow Ribbon' ('Yellow Ribbon' arborvitae; I) have outstanding pyramidal forms.

Conifers for specific needs. Try Juniperus×pfitzeriana 'Saybrook Gold' ('Saybrook Gold' spreading juniper; D) for a low, compact spreader, or use mounding Pinus mugo 'Aurea' ('Aurea' mountain pine; I) for showy foundation plants. For a site protected from winter sun, Picea orientalis 'Skylands' ('Skylands' Oriental spruce; I) has great color and form. Picea pungens 'Aurea' ('Aurea' Colorado spruce; I) and Pinus sylvestris 'Aurea' ('Aurea' Scots pine; D) change color from green to brilliant yellow in the winter months. For an eastern exposure, Abies koreana 'Aurea' ('Aurea' Korean fir; I) is outstanding. In general, Korean firs like cool morning sun. Never plant them in the hot afternoon sun, and keep the roots cool with coarse mulch.

Favorite, large-growing, blue cultivars include steel blue Picea pungens 'Hoopsii' ('Hoopsii' Colorado spruce; L), P.pungens 'Thomsen' ('Thomsen' Colorado spruce; L) and Abies concolor 'Candicans' ('Candicans' white fir; L).

Intermediate forms Abies lasiocarpa var. arizonica (Rocky Mountain fir; I), Picea glauca 'Coerulea' ('Coerulea' white spruce; I) and Picea abies 'Weeping Blue' ('Weeping Blue' Norway spruce; I) showcase great color. Pinus sylvestris 'Watereri' ('Watereri' Scots pine; I) and P.sylvestris 'Glauca Nana' ('Glauca Nana' Scots pine; I) sport blue-green needles, and they develop superior orange bark as an added feature.

Outstanding dwarf varieties include Picea pungens 'St. Mary's Broom' ('St. Mary's Broom' Colorado spruce; D), Abies lasiocarpa 'Glauca Compacta' (compact Rocky Mountain fir; D), Abies concolor 'Compacta' ('Compacta' white fir; D), Picea glauca 'Yukon' ('Yukon' white spruce; D) and Picea mariana 'Blue Tier Drop' ('Blue Tier Drop' black spruce; D).

Bicolor-needled conifers. Some conifers display bicolor needles of stripes, spots or patches. Bicolor-needled trees offer high interest and often tie various colors together. For example, Picea omorika 'Nana' ('Nana' Serbian spruce; D), P.omorika 'Pendula' ('Pendula' Serbian spruce; I), P.omorika 'Expansa' ('Expansa' Serbian spruce; I) and Picea bicolor 'Howell's Dwarf' ('Howell's Dwarf' alcocks spruce; D) highlight needles with green topsides and blue undersides.

Green and yellow variegation is found on Pinus densiflora 'Oculus-draconis' (dragon's eye Japanese red pine; I). A variegated thread leaf false cypress with green and creamy yellow foliage is Chamaecyparis pisifera 'Filifera Aureovariegata' ('Filifera Aureovariegata' sawara false cypress; D). Abies koreana 'Silberlocke' ('Silberlocke' Korean fir; D) displays recurved needles showing the white undersides of its curled foliage.

Challenge yourself to learn more about captivating conifers for the landscape because limited exposure makes for limited designs. Educate yourself by visiting gardens and displays. Meet the professionals passionate about the newer cultivars. Join the American Conifer Society, for the latest news on garden conifers and good photographs of the trees. Purchase new books on garden conifers that provide information you can pass on to your clients. Design landscapes with great plant material displayed in an artistic manner. Learn the value of dwarf plant material so plant size will remain in scale with its surroundings.

Promise to make the plants and your customers happy, and you will be rewarded for your efforts. Make your nursery, garden center or garden design unique with extraordinary plant material, and people will notice and remember you. Happy customers will expand your client base with many referrals.