Your choice of plants and their grouping and arrangement should reflect the garden style you are trying to create. A traditional approach for a border design is to line plants up in order of size, with the largest at the back and smallest at the front; beds work in a similar way with plants of ever-decreasing sizes fanning out from the tallest in the middle. Modernists have adopted a different approach, and use blocks of a single species to mirror Cubist paintings. English-garden designs interlink oval-shaped swathes of perennials to create a natural effect, while modern perennial designs are also inspired by nature, weaving together wide ribbons of tough hardy perennials and grasses to create an undulating landscape of flowers and foliage. Consider these designs when deciding how to group your plants:
• Traditional designs: To create a traditional border, either plant a hedge, or use shrubs and tall grasses to form a backdrop, and add perennials with contrasting leaf shapes and flowers in front. Pom-pom-headed alliums work well with floating grasses, while flat-headed achilleas make a good match for flower spikes. Edge the front of your design with ground-cover plants, compact grasses, and annuals to form a line of flowers.
• Contemporary blocks: Inspired by the modernist art movement, planting in blocks produces a clean, minimalist design. You can use a single species of grass, such as a Miscanthus species, which will have a dynamic effect when the leaves rustle in the wind; clumps of bulbs or perennials, such as irises; or heavier blocks of closely clipped box or yew. Set them out on an asymmetrical grid, and use lawns and pools to break up the planting.
• Woodland planting: Even small gardens can play host to a woodland design. Underplant a small collection of trees with shade-tolerant shrubs, grasses, ferns and other perennials that would naturally occur in similar sites in the wild, but don’t be tempted to cram in lots of different species, since this will look too styled. Add some meadow flowers in open areas around the trees and in brighter areas within your woodland to mimic a glade.
• Natural-looking designs: Contemporary designs combine a limited palette of hardy perennials and grasses in bold swathes to resemble a prairie or steppe landscape. These designs work best on medium-sized to large sites, but you can shrink them down to fit smaller spaces by reducing the number and diversity of plants. Perennials such as Rudbeckia, Sedum, and Eupatorium are ideal, combined with grasses like Stipa, Miscanthus, and Calamagrostis.
Where to Plant Certain Plants
When selecting plants for your garden, it’s important to test your soil and assess your site carefully before you start. Failure to do so may end in disappointment, with sun-loving plants in shady sites growing tall and gangly as they strain to find the light, or shade-loving plants scorching in full sun.
Test your soil’s acidity too, because mistakes can be costly if plants are given the wrong conditions. For example, azaleas, rhododendrons, camellias, and pieris only thrive in acid soil and will suffer in chalky, alkaline conditions. On the other hand, roses will not flower well, if at all, in a shady site, and their stems may grow tall and leggy. Therefore, they should be planted in open, sunny areas in nutrient-rich, moist but well-drained soil. Remember, too, that the soil close to a house wall or permanent structure will be significantly drier than other areas of the garden—these areas are called "rain shadows."