Landscape design is accomplished by both concept and plant materials. I prefer designing, initially, by concept. This means determining what you want your property to look like before deciding on the exact plants to use to achieve your goals. This method of designing your landscape is very effective, particularly for a garden's vertical and overhead planes.

Get started by laying out your concepts on paper; determine how you are going to use your space. Then consult an expert and decide what plants will fit your design. Because there are more than 9,000 plants identified in this country and more than 100,000 internationally, choosing the perfect one for your situation, without first knowing what you want the plant to do, will probably require some research and advice.

In more than three decades in the business, the number-one request from my clients has been screening to block unpleasant views, provide privacy or establish a barrier between their property and the neighbors. Screening can be achieved in a number of ways. But, if you know only one screening plant, such as giant arborvitae, then without research and talking with plant experts, you are left with only one choice.

Vertical Plane

Jay Appleton, a professor of geography emeritus at the University of Hull in Northeast England, described the human preference for refuge: "Refuge relates to the feeling you get within a secret place, where, from concealment, you might be able to see out without being seen by others."

It's human nature to feel secure and comfortable inside private, intimate enclosures. An enclosed garden area creates a relaxing atmosphere.

Some of the things that foster privacy are fences, walls, hedges, woods, masses of shrubs and trees. Design plant material to appear as though it's naturally occurring, rather than installing plants so they look as if they are hiding something. Soften a fence with shrubs and trees in groupings. Don't line a fence with a row of upright-growing shrubs. This will focus more attention on it.

Landscape design by concept can be achieved without knowing the plants' names. Specify to a plant expert that you want screening elements to fit the existing space. Bring drawings or photographs of the area. If appropriate, repeat the plantings in other parts of the garden to bring unity to your design.

While giant arborvitae might indeed be the answer for screening on the vertical plane, don't focus on one plant exclusively; develop concepts. All shrubs, grasses, vines and trees that grow in the range of 10 to 40 feet tall, along with fences and trellises, are vertical elements and, therefore, potential screeners.

I am not an advocate of surrounding yourself on the vertical plane with walls, fences and plantings everywhere on your property. However, be sure to design enough area to offer a private space where you can be alone and have the option to invite others in or not. Perhaps a section of fence would be enough of a screen, or several large conifers strategically located to block views. They offer screening with more of a parklike setting rather than the "Great Wall" effect of a fence or a formal hedge.

Groupings of trees and shrubs work well together. Use plants with upright and spreading branching habits. Design to create a physical barrier by planting several shrubs, a small flowering tree and some evergreens. Design for interesting flowers, foliage and bark.

One possible vertical-plane arrangement might be a hedge consisting of all the same plants, such as a row of Nellie R. Stevens hollies, fragrant osmanthus, or leatherleaf or Alleghany viburnum. If you add some showier elements to your design by including herbaceous annuals and perennials, the ornamental options are limited only by your imagination. Plant several large shrubs to the back of a bed as a screen, such as viburnum or boxwood. Then add tall, medium and short perennials to the front of the border.

Overhead Plane

The least-considered part of the garden is the overhead plane, which consists of the canopy, and serves to bring the landscape down to human proportion.

Shade trees and overhead structures create overhead enclosure. They are crucial elements in the garden, providing human scale and cooling shade, as well as enhancing the design. Trees add environmental benefits, too. They hold the earth's mantle, filter particulate and gaseous pollution, produce oxygen and add organic material to the soil.

Instead of choosing only trees that you already know, develop the criteria that you want, such as flowers, fall color, bird attraction and interesting growth habits. Then, go to the garden center and request trees that meet these criteria.

There are other overhead options, such as gazebos, pergolas and vine-covered arbors. Consider, if appropriate, using one or two of these elements in your landscape design in conjunction with shade trees. The structure's roof height and the lowest branches of a tree will have the greatest impact in determining whether an area feels large or small.

Tall trees, such as white oaks and tulip poplars, offer a monumental scale to the garden as they get older. Their lower branches are 20 feet above the ground. Other shade trees with lower canopies will bring the surroundings into smaller proportion. Some trees to help you achieve this because of their lower branching habits are river birch, large crape myrtle, paperbark maple, red maple, saucer magnolia, sweet gum and black gum.

The roof height of a garden shelter will also help to establish the intimacy of a landscape. If you wish to get the effect of privacy or enclosure, use a lower roof, one that is "people-sized" at eight to 10 feet in height.

These books will help you fill in the blanks in choosing plants that will meet the criteria, or concepts, that you develop: "American Horticultural Society A-Z Encyclopedia of Garden Plants" (DK Publishing Inc., 2004); "Dirr's Hardy Trees and Shrubs: An Illustrated Encyclopedia" (Timber Press, 1997); and "Armitage's Garden Perennials: A Color Encyclopedia" (Timber Press, 2000).

These books provide pictures of plants and descriptions by ornamental characteristics. However, the only way to know how plants will perform is to ask someone who has seen them grow. Find a plant expert at a garden center or nursery who's willing to exchange ideas. Otherwise, you will still just be picking plants by name.

Designing by concept for vertical and overhead planes is the easiest way to develop a vision of how you want your property to look. Do-it-yourself landscape designers who skip this step and immediately pick favorite plants often are not satisfied with the finished look of their properties, because plants must match concepts.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site,

A vine-covered pergola, left, is an overhead-plane option. Several large conifers, center, can offer screening with a parklike setting. With flowering perennials, right, plant large shrubs in the back.