Jennifer Schultz Nelson
Extension Educator, Horticulture
When you say fall flowers, most people immediately think of chrysanthemums. An equally beautiful choice for the fall garden, but one which is often overlooked is the aster.
The name aster comes from the ancient Greek word astron, meaning "star", referring to the shape of the plant's flowers. Originally, botanists classified almost 600 species of plants in Europe, Asia, and North America as belonging to the genus Aster.
The development of modern scientific methods such as DNA fingerprinting allowed botanists to reexamine how different plant species were related. Using these methods in the 1990's, many of the plant species formerly classified as the genus Aster were reassigned to other genera.
After this reorganization, only about 180 species remained assigned to the Aster genus, all but one native to Europe and Asia. The rest were assigned to other genera, but all remained within the Asteraceae family. Sometimes despite being assigned to another genera, plants have retained the name Aster as a common name, which can be confusing when searching for particular plants.
Asters come in a wide range of flower sizes and colors, but have the same basic structure. Other than their distinct star shape, they vaguely resemble daisies, one of their cousins. What we commonly call the flower is actually a grouping of hundreds of tiny flowers, or florets.
The center of each flower is filled with flat yellow to orange disc florets, the perimeter surrounded by ray florets which each have one colored petal attached. Aster petals can be many colors, from red to pink, blues to lavender and purple, and white. Most are an inch or two in diameter, but some species may be smaller.
The overall size of an aster plant ranges from six inches to eight feet tall, depending on the species and cultivar. Most cultivars for home gardens are in the six inch to three feet tall range.
Asters are split into two main groups, the New York and New England types. New York types tend to be shorter than about a foot, and New England types are generally taller.
Aster leaves are very long and narrow, and sometimes are a bit hairy. The plants themselves occasionally become leggy and flop over during the growing season. Pinching or shearing back periodically through midsummer will help encourage branching and bushy compact growth.
Most asters are grown for their fall blooms, but depending on the species, some bloom in the summer. One that I have planted is Frikart's Aster (Aster x frikartii) a selection made from a cross of Aster amellus x Aster thomsonii.
The original cross was made in Switzerland in the 1920's, and from it the cultivars 'Monch' and 'Wonder of Stafa' were selected. I grew the cultivar 'Monch', which caught my eye because of its lavender blue flowers with orange centers. It was perfect for my Illini garden.
Frikart's Asters are easy to grow, and hardy here in our Zone 5 climate. Hardiness is increased with winter mulching, and waiting to cut the plant back until spring. Mine survived its first winter just fine, but an early spring warm up followed by extended freezing weather unfortunately wiped out my Frikart's Aster.
Despite this early failure with Asters, I tried additional varieties which have flourished for multiple years in my garden. One isn't technically a member of the Aster genus, but has retained the common name Aster. Stokesia laevis 'Blue Danube' is commonly referred to as Stokes' Aster. 'Blue Danube' produces gorgeous showy blue flowers from late spring through frost.
The other Aster in my garden is just gearing up for its fall show. Aster oblongifolius 'Raydon's Favorite' is a star in my fall garden. This Aster is most similar to the New England asters, but flowers later. It is native to states that are part of the Mississippi River watershed. This plant took a little while to establish in my garden, but this year it is HUGE, about three feet tall and four feet wide. It starts flowering in September, and remains covered in tiny blue-purple flowers through frost.
Asters prefer well-drained soil in full sun. Once established, they will tolerate drought to some degree. They will also tolerate clay soil to some extent. They are susceptible to several fungal diseases if there is too much moisture present, including root rots.
Asters are one of the many plants susceptible to aster yellows, a disease caused by a tiny organism called a mycoplasma which is spread from plant to plant by leafhopper insect feeding. In general, affected plants appear yellow, and new growth is stunted and distorted. If plants are infected, they must be discarded to reduce risk of it spreading to other plants. There is no treatment and no cure.
Another great reason to grow asters is they are butterfly magnets. In the late summer and early fall, it is not uncommon to find multiple butterfly species enjoying the nectar of asters in the garden. The flowers are beautiful, and they attract butterflies- in my opinion, these are two great reasons to try asters in your fall garden this year.