Blazing Star (Liatris, often L. spicata or L. pycnostachya), is a distinctive perennial known for its tall, spiky columns of purple flowers. These native North American plants bring vertical interest to a garden and are highly attractive to pollinators like bees and butterflies. Blazing Star does spread, though generally in a manageable manner. Its expansion occurs through two distinct methods: the production of new plants far from the original through seeds and the slow, gradual increase in size of the existing plant clump.
Propagation via Seed Dispersal
The most noticeable form of spreading occurs when the plant reproduces by distributing its seeds, resulting in new plants appearing in unexpected locations. After the purple flowers fade in late summer and early fall, they develop into small, dry fruits called achenes.
Each achene is attached to a feathery structure known as a pappus, which functions like a small parachute. This adaptation allows the seeds to be carried by the wind and deposited a significant distance from the parent plant. Seeds can also be spread by birds, who feed on the seed heads, or by gravity, which drops them directly to the soil surface near the original clump.
For germination to occur, Liatris seeds require a period of cold, moist conditions, a process called cold stratification. This means that most seeds that drop in the fall will not sprout until the following spring, often leading to “volunteer” seedlings. While this spread is natural, it is the primary source of unwanted Blazing Star plants in manicured garden beds. New plants grown from seed often will not produce flowers until their second or third year of growth.
Localized Expansion Through Corms
The second way Blazing Star spreads is through the vegetative expansion of its underground structure. Liatris plants grow from a corm, a specialized, bulb-like, swollen stem base that stores nutrients. This corm is the perennial heart of the plant, producing the roots below and the foliage and flower spikes above.
Over time, the parent corm slowly produces small offset corms or cormlets around its perimeter. This annual production leads to the plant clump increasing in diameter and becoming denser. This growth is a slow, methodical process, not an aggressive spread.
The increase in size and density means that the clump will produce more flower spikes each year. Eventually, the center of the mass can become overcrowded. After about three to five years, the older, interior corms may stop producing healthy flower stalks, leading to a decline in plant vigor. This localized expansion signals the need for gardener intervention to maintain a healthy and floriferous plant.
Practical Management of Growth
Managing the spread of Blazing Star involves addressing both the long-distance seed dispersal and the localized corm expansion. To prevent the appearance of volunteer seedlings, the most direct approach is deadheading. This involves removing the spent flower spikes shortly after the blooms fade but before the seeds fully mature and disperse in the late summer or fall.
For those who want to prevent seedlings but still feed winter birds, the flower stalks can be left standing until late winter before being cut back. Choosing a site with full sun and well-drained soil also encourages vigorous, upright growth, which can naturally reduce floppiness and excessive self-seeding.
To manage the dense clumping caused by corm expansion, occasional division is necessary to rejuvenate the plant. Plants should be dug up and divided every three to five years. This division is best performed in the early spring, just as the new shoots are beginning to emerge.
The corm mass can be separated using a sharp knife, shovel, or saw, ensuring each section retains at least one healthy “eye,” or growth bud. Replanting the divided corms in new locations or spacing them out helps to thin the clump, which promotes better air circulation and ensures the plant continues to produce robust flower stalks.