Be generous when marking out the area for your bed or border. If you can afford the space, allow at least 10 ft (3 m) to provide a good planting width. You can then build up several layers of plants, one behind the other, and use shrubs and climbers to create height toward the back. If the choice is between two narrow borders and one deep one, you’ll find the larger more rewarding, however intimidating it may seem at first.
Choosing the Key Plants
Working from an accurate base plan makes designing a new bed or border
easier, and helps you decide how many plants you need to fill it. When
selecting plants, think of your border as a stage performance, and pick
out the leading cast. This should include plants that have an important
presence because of their handsome shape, decorative leaves, or long
flowering season. Good candidates include colorful foliage shrubs, such
as berberis and cotinus, and many of the grasses, sedums, and
euphorbias. Repeating these every few yards brings rhythm into a plan.
Think of where you would like to see your stars: sedums flower in fall
and are good front-of-the-border plants, while taller grasses, such as
molinia or calamagrostis, are better placed in the middle or background.
Mark the plants on your plan with a circle representing their final
spread. Most of the larger perennials will spread to 18 in (45 cm),
while smaller ones will reach 12 in (30 cm); check plant labels for the
spreads of shrubs, and note that their size can be affected by your soil
and garden conditions.
Planning in Color
Once the key plants are on your plan, choose supporting players that
offer more subtle effects. Keep a note of their flowering times and
colors, and, if in doubt, make an overlay with tracing paper, onto which
you can mark the color of each plant using different pen types or
symbols. Do a few overlays for the different seasons to show when your
chosen cast is in flower, where the gaps are, and at what time of year
they need to be filled.
Contrasting Flower Shapes
Think of the contrasts in flower shape as well as color, height, and season. Plants with spiky flowers, such as veronicas, delphiniums, foxgloves, and verbascums, or upright, linear foliage, such as irises or daylilies, will introduce a vertical accent. Those with round, disklike flowerheads, such as sedums, yarrows, fennel, and all the cow-parsley relatives, create a horizontal plane. Mixing these two types of flowers paints an exciting picture. Distinctive spherical shapes, such as alliums and Echinops ritro, add to the structure.