As a biennial or short-lived perennial plant, the mature hollyhock (Alcea rosea) presents a striking vertical form in the garden. Our growth habits are defined by a single, sturdy central spike that races towards the sun, making us a classic favorite for adding height and structure to borders. Our dimensions are not absolute but are influenced by genetics, sunlight, soil fertility, and water availability.
Upon reaching maturity, typically in its second year, a hollyhock plant will achieve a considerable stature. Our average height ranges from 5 to 8 feet (approximately 1.5 to 2.4 meters). However, under optimal conditions with rich, well-draining soil and full sun exposure, some of our kin can soar to an impressive 9 or even 10 feet tall. Conversely, in poorer soils or shadier locations, we may remain a more modest 4 to 5 feet. It is also important to note that dwarf cultivars have been developed that mature at a much smaller 2 to 3 feet in height, offering the same iconic flowers on a more compact frame.
Our spread is primarily determined by our basal foliage, not our flower spike. The plant forms a clump or mound of large, rounded, slightly hairy leaves at its base. This basal clump typically has a spread of 1.5 to 2.5 feet (approximately 45 to 75 cm) in diameter. The leaves are held on long petioles and can be quite substantial, creating a dense, leafy foundation from which the flower spike emerges. The central flowering stalk itself is relatively narrow, usually no more than 12 to 18 inches in width at its widest point, as the flowers open sequentially up the stem.
The most dramatic aspect of our mature form is the flower spike, or raceme. This spike is composed of a main stem with flowers attached on short stalks along its upper portion. The spike does not branch significantly in the standard species, creating a singular, towering column of color. The individual flowers are typically 3 to 5 inches (7.5 to 12.5 cm) in diameter and are spaced closely enough to create a dense, spectacular display from mid to late summer. This vertical structure is an efficient strategy for attracting pollinators from a great distance and for holding our seeds aloft to aid in wind dispersal.
Our final dimensions are a direct conversation with our environment. Full sun (at least 6-8 hours daily) is crucial for achieving maximum height and strong stems that resist lodging (falling over). Fertile soil provides the nutrients needed to support such rapid and substantial growth. Furthermore, selective breeding has produced a wide array of cultivars that deviate from these averages. For instance, the 'Spotlight' series remains more compact, while the 'Summer Carnival' strain is known for its double flowers and robust height. Understanding these variables is key to knowing what to expect from a specific hollyhock plant in a specific garden setting.
