If you think of your garden as a work of art--as it undoubtedly is on its good days--it's important to keep in mind a few basic principles that can make your landscape a triumphant opus rather than merely a competent arrangement. Designing a distinctive garden that really works means incorporating unity, rhythm and repetition. Tall, spiky annual plants can help.
Clumps of interesting foliage rhythmically repeated throughout a garden bed will unify the garden and transform it ordinary to sophisticated.
Cannas bloom, but the more interesting varieties such as 'Tropicana' and 'Pretoria' have variegated leaf patterns. Cardoon (Cynara cardunculus) adds a fascinating spiky texture. This plant requires well-drained soil. New Zealand flax (Phormium tenax) has strappy red foliage that is hardy in locations where winter temperatures stay above 20 degrees. 'Purple Majesty' millet (Pennisetum glaucum) feeds the birds as it perks up your design. It can even prop up your flopping cosmos (Cosmos bipinnatus).
Color for Easy Unity
These tall annuals will sow themselves, which makes a gardener's work easy. Simply weed out the seedlings that are out of place. The result will be a unified picture that is simply beautiful from a distance.
Sunflowers (Helianthus annuus) call in the birds and lend a happy personality to your garden. Seeds can be planted directly in the garden in spring. Woodland tobacco (Nicotiana sylvestris) is as fragrant as it is beguiling. It will grow to 6 feet in height and 1-2 feet wide, so give it ample space. Wheat celosia (Celosia spicata) is available in purple and pink. Both are excellent garden companions for other flowers, and also make good cut flowers.
Foxglove (Digitalis purpurea), a biennial, is deer-proof. It blooms in summer, then drops seeds which germinate readily and often bloom the following year. Tall verbena (Verbena bonariensis) is the classic "see-through" flower. Even though it's tall, you can plant it in the foreground as well as the rear.
Cool and Unusual
Every gardener wants a few plants that will stop neighbors in their tracks. Three or five of any tall, intriguing plant, spaced at orderly intervals, will do just that.
Lion's tail (Leonotis leonurus) is a fascinating orange flower in the mint family. It's very tall and blooms in late summer or early fall. Angelica (Angelica gigas) blooms the second year from seed, but you can often find nursery-grown varieties of this stately flower, which is the color of red wine. Clary Sage (Salvia sclarea), an old-fashioned biennial, is bee-friendly, deer-proof, and at home in the herb or flower garden.
'Red Shield' hibiscus makes an ideal companion to zinnias. For rhythmic balance, space this dark-leaved beauty every 6 to 10 feet in a bed of cutting zinnias.