Hollyhocks are classic perennials that add charm and color to the mid to late summer garden. The flower spikes are also showy in cut-flower displays. Growing quite tall, sometimes up to 8 ft. tall, these perennials grow best in full sun and are often planted as a backdrop for other flowering plants. They're also a favorite for planting in cottage gardens and along fences and walls. Available in an array of colors and in single and double flower forms, they reliably return year after year. When buying hollyhock perennials for sale online, make sure they are suitable for your grow zone. Other considerations are their flower color and mature height and spread.