The Hampton Gardener: Aster

If you happen to drive up to New England during the summer taking route 684 you can’t help but notice the miles and miles of lythrum that grows on the roadside, in the median strip and in the culverts. Toward the end of the summer, these pinkish to purple flowers begin to fade and are replaced by the glowing faces of the sundrops (oenothera) and in early September your eye will undoubtedly be caught by the radiant yellows of the goldenrods, which then get replaced by the vibrant purple glow of the asters.

The same thing in a slightly less vibrant fashion has happened to me driving down the winding roads from the Shinnecock golf course toward the National and the bay. WHAM, out of nowhere, like a horticultural bolt of lightning, the asters jump into view. Indeed, with all their vibrant color, these asters are a harbinger of fall and while there are asters that bloom in April (Aster alpinus) and annual asters that can be grown through the summer, it’s the fall asters that are striking, bold and should be an important part of the later summer/fall garden and landscape.

We are particularly blessed with having two native asters, one of which has a very interesting history. The New York aster, Aster novae-belgii, meaning New Belgium, reveals the classic thinking of Linnaeus, who bestowed the name on it. Linnaeus knew that the Dutch had first settled the area that later became New York. Searching for a classical synonym for New Netherlands, he found that the original Roman province, which included modern Holland, was named Belgica. Thus it was logical to name this the New Belgium aster, novae-belgii.

The plant was brought back to England in the mid 19th century and through hybridization and reselection, British horticulturists developed the Michaelmas daisy, now a repatriate well known to American gardeners. The plant also found its way to Germany where extensive breeding and selection was conducted well into the 20th century.

As a rule, asters are hardy, leafy stemmed perennials with clusters of flower heads. Individual flower heads consist of many flat rays or petals that are colored white, blue, red or purple and a central “eye” or disk, which is generally yellow. Most varieties bloom from late August until mid-fall and some will continue until we have a hard frost. When looking at the flowers, many are reminded of a multi-pointed star and in fact the Greek word aster means star.

While some try to grow these plants from seed, which is fine for the wild species, the only way to ensure that you get a plant that is true to name and color is to buy from reputable nurseries (mail-order or local) or to make your own root divisions or stem cuttings. Clumps of roots of mature plants can also be divided into single or multiple divisions with one three-year-old clump yielding as many as 20 single plants that will mature in just a year.

These plants are generally vigorous growers that do well in sandy to organic soils and will grow in full sun to partial shade. While pages and pages have been written about disease and insect problems with asters, I’ve never been deterred from planting them and with the usual care that you’d give to any plants in your garden they should perform well. Mildew problems can be fairly easily avoided by letting the plants have plenty of air circulation and this means dividing the plants every few years. Having said that, it’s only fair to also add that the asters can get a bit tall—some to 8 feet—and some will need staking or they can get floppy.

Some tricks may also apply well here. Staking can be reduced and in many cases eliminated in many of the mid-sized cultivars if the plants are grown in full sun and pinched back once or twice in spring and early summer. This is a good practice for the tall varieties as well and will result in compact, dense plants, if that’s what you want. Pinch back 2 to 3 inches of growth from each growing tip no later than June 15.

Aster x frikartii, or Frikart’s aster, flowers in late summer with lavender flowers and grows to 3 feet tall with a similar spread. The foliage is mildew resistant and remains disease-free throughout the season. Flowering starts in late July and continues for about eight weeks. Plant in full sun and fertilize only once in the spring. Some gardeners have told me that they’ve had trouble overwintering this hybrid and the problem may be wet winter soils. If you have the good fortune of having a heavy organic soil, try mixing it with equal parts of clean sand to root depth and this should solve the problem.

There are two cultivars of this aster. Monch is said to be the best frikartii, being similar in habit to the parent. Wonder of Staffa has lighter blue flowers than Monch and may be slightly taller, but even the best of gardeners have been known to confuse the two.

Several cultivars of the New England aster, Aster novae-angliae, are of note: Alma Potschke is a stunning bright rose selection that grows to 4 feet with 2-inch flowers that have slightly curled petals. It is more compact than others in this group, but still needs staking. Harrington’s Pink was developed in Iowa by Mrs. Harrington, of course. This plant grows to 5 feet, bears salmon-pink flowers and is one of the latest bloomers.

In the cultivars of the New York asters, there are three classes: The dwarfs are less than 15 inches tall, mediums are less than 4 feet tall and the taller types are 4 feet tall and up.

Each group has at least half a dozen cultivars in a wide range of colors and the dwarfs and mediums make a nice replacement for the time-worn fall mums.

When using asters in the garden, remember that they are daylight sensitive. During the long day periods of the summer they make most of their vegetative growth and as the days shorten they set their buds for the late blooms. However, if you put these plants in areas where they get less than full sunlight in July and August they can bloom up to two weeks earlier than the same plant that’s grown in more light.

The aster that I think is most spectacular sits hidden behind a clump of tall miscanthus in my garden. You can’t see the foliage or any part of the plant until late August when it begins to reach 6, 7 then 8 feet in height, but you can never miss it once it’s in bloom. This plant is Aster tataricus, or the Tartan Aster, from Siberia. In its first year, this plant rarely grows to more than 4 or 5 feet tall and at this stage it looks like one humongous weed with leaves 6 inches wide and up to 2 feet long. The second year, however, the plant pushes for the sky and when it gets there (the one I remember most was nearly 8 feet tall and hidden for most of the season way in the back of the garden) the flower stems branch near the top resulting in many spectacular blue to purple ray flowers with yellow centers.

Flowering starts in September and may continue until late October and November. Look for asters in garden centers now or in the spring, but the largest selection is probably available from mail order and internet nurseries.

Keep growing.

Andrew Messinger has been a professional horticulturist for more than 30 years. He divides his time between homes and gardens in Southampton, Westchester and the Catskills. E-mail him at: Andrew@hamptongardener.com. The Hampton Gardener is a registered trademark.