Want some color and height at the back of your flower garden, but not interested in shrubs? There are many tall flowers that can anchor the back of a border. Which ones you choose will depend on the space available (some of them are as wide as they are tall) and on your growing conditions.
Foxgloves, for instance, will grow to 6 feet if they’re in moist, nearly neutral soil in semi-shade, but they might top out a bit below 4 feet if they’re in average soil in the sun. The same goes for black snakeroot (Cimicifuga racemosa), which might stretch to 7 feet or more if happy and dwindle utterly if not.
Foxgloves are usually columnar, their tall flower spikes rising almost leafless from a broad rosette at the bottom. Snakeroot is rangier; sending out beautifully cut-edged leaves almost all the way up the stem. Meadow rue (Thalictrum spp.) also sends out leaves all the way up, but they, like the flowers, are lacy and delicate, so the overall effect is light. T. rochebrunianum, which has purple blooms, and T. speciosissimum, (aka T. flavum ssp. glaucum), which has pale yellow flowers and bluish leaves, are both 4 to 6 feet tall. White-flowered T. polygamum can grow to 8 feet.
Other tall flowers include delphinium, Caroline lupine (Thermopsis caroliniana), plume poppy (Macleaya cordata), Ligularia spp., Japanese meadowsweet (Filipendula purpurea), foxtail lily (Eremurus stenophyllus), Joe Pye weed (Eupatorium purpureum), and globe thistle (Echinops bannaticus). Read cultural descriptions carefully before you buy; many of these plants have very specific needs and some — especially plume poppy and Joe Pye weed — are very aggressive spreaders.