Symphyotrichum praealtum aka Willowleaf Aster

Symphyotrichum praealtum is also known as willow aster. It is an herbaceous perennial: a plant with soft stems that lives for years. It belongs to the daisy family, Asteraceae. Its native range spans southeastern Canada to central Mexico. It grows in temperate zones and likes moist ground. Wild plants grow in wet prairies, ditches, and open woods. They also grow by lakes, streams, fields, and roads. They can form dense groups, or colonies, in these sites. Its older scientific name is Aster praealtus.

In gardens, willow aster grows 2–5 feet [0.61–1.52 metres] tall. It can spread to 4 feet [1.22 metres]. Narrow leaves grow along the stems in an alternate pattern. This means they grow in turn, not in pairs. Their shape gives the plant its common name. Small teeth line the leaf edges. Leaves reach about 0.42 feet [0.13 metres] long. They reach about 0.06 feet [0.02 metres] wide. The leaf undersides look pale whitish-green. A clear network of small veins marks this surface.

Groups of flowers form near the stem tips from August through October. Each flowerhead grows up to about 0.08 feet [0.025 metres] across. Pale lavender ray florets ring a yellow center. These showy blooms draw butterflies. They also add color late in the season. Group plantings suit the way this plant forms colonies. It suits native plant gardens, cottage gardens, and moist borders. It also fits prairie plantings and open woods. Other uses include rain gardens and pond edges.

Grow willow aster in rich, moist loam. It accepts full sun or part shade and tolerates wet soil. Its listed hardiness range is USDA zones 4–8. It needs little care and grows with ease from seed. Plants can grow many new seedlings without help. After bloom, cut stems to the ground to curb unwanted seedlings. This also clears leaves that no longer look good. Pinch stems several times before mid-July for shorter, bushier growth. This may cut the need for stakes.

Serious pest and disease problems are not usual. Powdery mildew, leaf spots, and rust can still occur. Leave space for air to flow through the plants. This helps reduce leaf disease. Tall stems may need stakes or some other support. Leaves can lose their looks by late summer. The plant may still bloom at that time.