Rudbeckia is also known as black-eyed Susan or yellow coneflower and grows in U.S. hardiness zones 2 to 11. Rudbeckia loves the sun and grows to heights of 2 to 3 feet. A drought-tolerant plant, rudbeckia does well in a slightly acidic soil that drains well. Plant the clumping flowers between 12 to 18 inches apart so the plants have plenty of room to spread. Deadhead the spent flowers to promote blooming during the entire growing season.
Echinacea is known as purple coneflower, but this plant comes in several colors, including white. Echinacea grows to a height of 3 feet or more when it is fully mature. Plant in full sun in well-drained soil. A native to the eastern part of North America, echinacea grows in U.S. hardiness zones 3 to 8. This plant does reseed itself if the dead flowers are not removed. Echinacea can be propagated by division.
Growing 2 to 4 feet tall, gold yarrow prefers the full sun and a rich soil. Gold yarrow is also known as an herb and does well at the back of the herb garden. Hardy in U.S. planting zones 3 to 9, yarrow makes a good cut flower, lasting for a week or more. Yarrow varieties also bloom in shades of pink and white. This plant does not tolerate wet soil and may rot if exposed to excessive moisture.
Delphinium produces tall spikes of pink, purple or white bell-shaped blooms, in full sun. This perennial grows from 3- to 8- feet tall in well-drained soil. Delphinium grows in U.S. hardiness zones 3 to 7 and, unless reseeded, may only last two to three years in the garden. Allow the seeds to overwinter outdoors for germination in the spring. Delphinium is susceptible to powdery mildew and aphids and should be treated as soon as a problem is detected.