It is important to gage the potential height of perennial plants before placing them in the garden. These plants are likely to be part of your garden for a long time. Tall perennials are best placed towards the back of beds or against buildings and fences. They are also useful placed at the base of slopes. Floating beds seen from both sides should have the tallest perennials positioned in the center.
The coneflower (Echinacea purpurea) is a native species has a medium purple ray-type flower with a pronounced orange seed cone. The stems will easily reach 3 to 4 feet in height. There are white, orange, gold, yellow and red varieties of coneflower. There are also dwarf forms, so check the size of each variety before choosing. This flower is a nice addition to the wildflower garden, and will attract butterflies and bees. Coneflowers are hardy in all USDA zones.
Bee balm (Monarda didyma) is a tall, fragrant flower. The red varieties are the most favored by gardeners, hummingbirds and bees. Some varieties suffer from powdery mildew, so seek out disease-resistant varieties like "Jacob Cline." The leaves and flowers can be used in teas and salads. The flavor is reminiscent of Earl Grey tea. The spiky flower petals stand out in the garden. Bee balms do well in full sun or partial shade.They are hardy in USDA zone 2.
The flowering sages (Salvia) are a varied group. There are culinary sages and ornamental sages. The tall perennial sages can fill in quickly and are a great accent for the naturalistic garden. A salvia for USDA zone 8 and higher is anise sage (Salvia guaranitica, or "black and blue"). This is a 3- to 4-foot plant with cobalt blue flowers that bloom in late summer. There are two medium blue sages (Salvia sylvestris, or "blue hill," and Salvia nemerosa, or "may night") that are better suited for colder regions. These are hardy to USDA zone 2.
Japanese anemone (Anemone hybrida) appears more like a foliage plant in early summer. The bold green leaves are a wonderful backdrop for other perennials. The white flowers are held on tall stems far above the foliage. Japanese anemone is also available in pink and double-flowered varieties. They are hardy to USDA zone 2.
Another tall perennial for full sun is cape fuchsia (Phygelius). This flower is more of a sub-shrub, leaving behind a woody base. It can be cut way back to keep it under control. The tubular flowers come in white, cream, salmon, pink and red. Many of the flowers also have yellow throats. This is a premiere hummingbird plant. The long stems are covered with glossy leaves that look attractive even when out of bloom. Cape Fuchsia is hardy to USDA zone 4.
False indigo (Baptisia) is a tall clump-forming perennial. Spires of smoky blue flowers appear in early summer. There is a white form ("alba") and an attractive pale yellow indigo ("Carolina moonlight"). These native wildflowers are hardy to USDA zone 3.
Jupiter's beard (Centranthus ruber) is one of the most versatile perennials. Clusters of tiny red flowers bloom from early summer until frost. This is a favorite of the Swallowtail butterfly. There is an equally valuable white form ("alba") that also exudes a sweet fragrance. Both forms are easy to grow in average sunlight. Jupiter's beard is hardy to USDA zone 2.