Mixing It Up

With the profusion of plants available these days, a walk through the nursery or even just flipping through the stack of trade publications on your desk can make your head spin. This huge selection is both a blessing and a curse. I joke with my colleagues about sometimes having “option paralysis” when I am designing: so many plants to choose from that I'm overwhelmed and fall back on my old standbys. In the end, I feel like I'm in a rut and fear my designs reflect it. That's why its essential to make good plant selections and revitalize your landscape projects as a result.

Many times plants are selected based on the function they will serve in the landscape. Examples might include a low hedge to direct foot or vehicular traffic, to screen an undesirable view or to accentuate a building entrance. With this function in mind, you should base plant selection on the environmental requirements and the aesthetic qualities of the plant. And because a healthy landscape is a growing and ever-changing entity, you also have to consider the maintenance it will need after installation.

ENVIRONMENTAL FACTORS

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Environmental requirements for a plant include a its low- and high-temperature tolerances as well as light, soil and moisture needs. You should meet these requirements first because matching a plant to the environmental conditions of the site is vital to its success. Keep in mind that every plant tolerates a range of conditions for each of these environmental factors. Sometimes you can create a microclimate to modify the environment around a plant. One example would be to make an area warmer or less windy, which might allow you to grow a species that tends to be marginally hardy in your zone.

AESTHETIC QUALITIES

The aesthetic qualities of a plant are what make it unique. I tend to characterize these qualities under a few broad categories including form, texture, color, flowering and fruiting habit, and mature size.

Form

Plant form is described as the outline of the plant as a result of its three-dimensional mass. Tree and shrub forms make up the “bones” of the landscape and they create the background for the rest of the design. It is these bones that create the silhouettes against the gray winter sky and provide interest in the landscape once the flowers have faded, herbaceous perennials have died back and deciduous leaves have dropped. Some common plant forms include rounded (Anthony Waterer Spirea; Spiraea x bumalda ‘Anthony Waterer’), oval (Greenspire Linden; Tilia cordata ‘Greenspire’), columnar (Columnar European Hornbeam; Carpinus betulus ‘Columnaris’) and pyramidal (Emerald Arbrorvitae; Thuja occidentalis ‘Emerald’).

Landscapes with a variety of plant forms are attractive, but too much variety in a small space can be chaotic. Depending on the size of the landscape, select a few forms and repeat them throughout to achieve some continuity. It doesn't have to be the same plant, just the same form. The rounded forms of the small shrub Anthony Waterer Spirea; the large shrub European cranberry viburnum (Viburnum opulus ‘Roseum’) and the Eastern redbud tree (Cercis canadensis) all work well together and provide form repetition in the landscape. Be sure to select a plant based on its natural form, not the form achieved by constantly pruning it.

Texture

Texture is the visual relationship of the foliage and twig size to the remainder of the plant. Just because a plant is large, doesn't mean it has a coarse texture. For example, a white pine (Pinus strobus) can be 50 feet tall and 40 feet wide, but it has a fine texture because the needles are narrow and flexible and the branching habit tends to be slender. In contrast, a bigleaf hydrangea (Hydrangea macrophylla) is 6 feet tall and wide at maturity, and is considered coarse textured because of the large leaves and flowers in relation to the overall size of the plant. A majority of ornamental plants fall into the medium texture category. Just as with form, it is important to incorporate a variety of textures in the landscape, but don't over do it or the result may be a little visual chaos.

Color

My eye is always drawn to a colorful landscape. Color is an important factor to consider, but because it tends to be temporary due to bloom time and fall color persistence, it shouldn't be the only thing. Select flowering plants based on when they will provide color and for how long, as well as the actual color. By carefully selecting trees, shrubs, perennials and annuals, you can overcome that temporary color impact and have color in the landscape almost year round.

You can group flower colors as those with warm tones (orange, red, yellow) or cool tones (green, blue, purple). Selecting plants with the same tone creates a harmonious planting combination. For a sunny spot, a warm tone combination that will provide color throughout the spring and summer could be forsythia, corydalis (Corydalis lutea), annual marigolds and salvias, nasturtium (Tropaeolum majus), Red and Gold sneezeweed (Helenium autumnale ‘Red and Gold’) and chrysanthemums. A cool tone combination for shade might include pig squeak, (Bergenia spp.), columbines (Aquilegia spp.), hostas (Hosta spp.), coral bells (Heuchera spp.) and violets (Viola spp.).

One of the great things about using color is that by changing out just a few existing perennials or adding in a new annual color bed, the landscape can take on a whole new look. Do some armchair color gardening online, at the bookstore or in the library. Gardening books and magazines are a great source of new ideas. They are loaded with pictures of inspiring gardens and planting combinations. And because the magazines are timely, you'll probably find information on the hottest trends. If you still aren't sure about some of these color combinations, talk to a particularly adventurous client to see if they are up for a small-scale planting trial on their site. Or, if the plants are small enough, pot up a few containers to see how they look together and evaluate how well they bloom.

Although flowers are eye-catching, don't over look plants with colorful bark, fall color or fruit. Serviceberry (Amelanchier arborescens) is one of my favorite “four-season” plants. It has showy white flowers in spring, beautiful blue-green leaves in summer that change to a striking yellow-orange in the fall, small dark-blue fruit in late summer and silky-smooth gray bark all year long. In addition, its multi-trunk branching habit gives it an interesting form all year long, and the medium texture makes it a complement to other ornamental plants.

One of my favorite groups of plants are the Viburnums. Not only do most of the species have good form, interesting texture and attractive yellowish fall color, they also provide a variety of flowering times. Many are deciduous but some are evergreen or semi-evergreen. Granted, not all of the species are hardy in the coldest of zones but there are still plenty of species and a number of cultivars to choose from. Some of my favorites include: Blue Muffin viburnum (Viburnum dentatum ‘Christom’), Onondaga viburnum (Viburnum sargentii ‘Onondaga’), Lantanaphyllum viburnum (Viburnum x rhytidophylloides), Doublefile viburnum (Viburnum plicatum var. tomentosum ‘Mariesii’), Alfredo American cranberry viburnum (Viburnum trilobum ‘Alfredo’) and Spring Bouquet viburnum (Viburnum tinus ‘Spring Bouquet’).

Flower and Fruiting Habit

Selecting plants with varied bloom times creates a landscape that blooms for the entire growing season. After the flowers are gone, many trees and shrubs will set fruit. Sometimes this can be a benefit because the fruit will attract wildlife to the landscape, but other times the fruit may be a nuisance. In this case, limit the number of fruiting species and, if possible, locate them in the landscape where they will not create a litter, maintenance, or pest problems.

Mature Size

Healthy plants grow. As such, the mature size of the plant must be considered in light of where it will be sited in the landscape. A common mistake is to select plants that soon become too large for their location. Regular and drastic pruning shouldn't be required to keep a plant in bounds.

MAINTENANCE REQUIREMENTS

Without regular maintenance, even the best-designed landscape can become self-defeating. Be sure that maintenance requirements are factored into your landscape plan. Some plants, particularly deciduous trees and shrubs, require more pruning and fertilizing when they are young and less as they mature. Needled evergreens are relatively maintenance-free regardless of age. Herbaceous perennials and annuals, on the other hand, tend to have a seasonality associated with their maintenance. Many perennials need to be pruned to the ground in the spring and some may need to have the crown protected with mulch in the fall. Once planted in the spring, annuals benefit from regular and frequent fertilizing throughout the summer and some need frequent dead-heading in order to continue blooming. Even though these annuals need a little extra time and attention, their striking appearance is worth the effort.

CHANGE IT UP

Although plant selection can become a repetitive, mind-numbing chore, I contend that it can also be perhaps the most rewarding and interesting part of creating a beautiful and functional landscape. If your plant knowledge is limited, or even if you just need some new inspiration, a number of reference books are available to help you make well-informed decisions. For me, the goal is not only to get the right plant in the right place, but also to use a variety of plants to diversify my landscape plantings. Try something new next time you need to select plants for a project. Don't give in to “option paralysis.” Give the old standbys a rest.

Ann Marie VanDerZanden, Ph. D., is an associate professor of horticulture at Iowa State University (Ames, Iowa).

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