Asters are popular for their vibrant, late-season color, providing blooms when much of the garden fades. Whether asters return every year depends on the specific variety, as the term “aster” applies to plants with different life cycles. Most popular garden varieties are dependable perennials that regrow annually, but some types are strictly annuals and will not survive the winter.
Understanding Aster Life Cycles
Most asters sold are herbaceous perennials. This means the top growth dies back in winter, but the root system remains alive to sprout new growth the following spring. These perennial types, often native to North America, are now largely classified under the genus Symphyotrichum. Classic examples include the well-known New England Aster (Symphyotrichum novae-angliae) and New York Aster (Symphyotrichum novi-belgii). They reliably return each year and are generally hardy in USDA zones 3 through 9, depending on the species.
In contrast, the annual aster, most commonly the China Aster (Callistephus chinensis), completes its entire life cycle in a single growing season. This type grows from seed, flowers, produces seed, and then dies completely with the first hard frost, requiring replanting each spring. Knowing the botanical name helps determine if the plant is a long-lived perennial or a single-season annual. Perennial asters planted within their appropriate hardiness zone are expected to return.
Overwintering Care for Established Plants
For perennial asters to successfully return, their established root crowns need proper preparation to survive the winter dormancy period. The most important factor for winter survival is ensuring the plant is in well-drained soil. Excessive winter moisture combined with cold temperatures can cause the roots to rot, making asters planted in soggy areas more likely to fail than those in drier ground.
After the perennial aster has finished blooming and the foliage has been killed by a hard frost, you have the option to cut the stems back to a few inches above the soil line. Some gardeners choose to leave the spent stalks and seed heads standing over winter, which provides cover for beneficial insects and a food source for birds, then cut them back in early spring. Applying a light layer of organic mulch, such as straw or shredded leaves, over the root zone after the ground freezes helps maintain a consistent soil temperature. This mulch layer prevents the repeated freezing and thawing cycles that can heave the plant’s roots out of the ground.
How Asters Spread and Multiply
Perennial asters increase their presence in the garden through several natural multiplication strategies, which is why a single plant can eventually become a large clump. One of the primary ways they expand is through rhizomatous spread, where some varieties send out underground stems that develop new shoots a short distance from the parent plant. This creeping growth habit causes the plant to form a wider, denser clump over time.
Another method of multiplication is self-seeding, especially if spent flowers are left on the plant through the fall. The seeds drop to the ground and may germinate the following spring, producing new, often smaller plants near the original. However, seedlings from hybrid cultivars may not look exactly like the parent plant because they are a genetic mix.
To maintain plant health and vigor, perennial asters benefit from division every three to five years. Division is necessary when the center of a mature clump begins to decline or flower production lessens. Digging up the plant and separating the healthy, outer portions of the root ball will create entirely new, rejuvenated plants. This division is typically performed in early spring as new growth emerges.