Asters are perennial flowering plants belonging to the expansive Asteraceae family, bringing vibrant, daisy-like color to the late-season garden. When planning a garden, a gardener must consider the plant’s final size, which is highly variable for asters. Their mature height depends greatly on the specific species or cultivar selected and the conditions where they are grown. This genetic potential ranges from low, mounding groundcovers to towering border plants, allowing asters to fit nearly any landscape need.
Categorizing Asters by Mature Height
The diversity of asters means their mature size can vary dramatically, from six inches to over six feet tall, requiring categorization for practical gardening purposes. Dwarf varieties are genetically programmed to remain short and compact, typically staying under one foot (30 cm) in height. Examples include the Alpine Aster (Aster alpinus) and cultivars like ‘Professor Anton Kippenberg,’ which are perfect for rock gardens or the front of a border.
Medium-height asters generally mature between one and three feet (30–90 cm) tall, fitting well in the middle of a perennial bed. The Smooth Aster (Symphyotrichum laeve) and certain New York Aster (Symphyotrichum novi-belgii) cultivars, such as ‘Marie Ballard,’ fall into this group, providing a dense, bushy habit.
Taller asters are the most dramatic, growing from three to six feet (90–180 cm) or more, and are best suited for the back of a border or as vertical accents. The New England Aster (Symphyotrichum novae-angliae) is the most well-known tall type, with cultivars like ‘Harrington’s Pink’ easily reaching five feet. The Tatarian Aster (Aster tataricus) can occasionally grow up to eight feet.
Environmental Influences on Final Height
While the selected variety sets the genetic ceiling for height, environmental factors modify the plant’s final stature and growth habit. Light exposure is a primary influence; asters grown in insufficient sunlight will experience etiolation, where stems stretch out and become “leggy” as the plant reaches for light. Full sun encourages a more robust, sturdy, and shorter plant with denser branching, preventing the floppy growth often seen in shaded conditions.
Soil composition and fertility also play a role in determining height. Asters generally prefer well-drained, average soil, but soil overly rich in nitrogen can lead to excessive, soft growth. This rapid growth produces weak stems prone to bending or collapsing under the weight of the late-season flowers. Moisture levels further affect this outcome; dry conditions can stunt overall height, while overly wet soil can lead to root problems that limit above-ground growth.
Techniques for Height Management
Gardeners can actively manage the height and structure of their asters through specific pruning techniques to encourage a more compact and self-supporting form. The most common method is the “Chelsea Chop,” which involves cutting back the stems by one-third to one-half in late spring or early summer. This timing, typically around late May to early July, removes the apical bud, the primary growth point, thereby stimulating lateral branching.
This intentional removal results in a bushier plant with multiple flowering stems that are sturdier and shorter than a single main stalk. Although the Chelsea Chop may delay flowering by several weeks, it reduces the need for external support later in the season. For the tallest varieties, such as New England Asters over four feet, staking or caging may still be necessary. Supports should be installed early in the growing season before the plant reaches its full height and begins to flop.