Sunday, October 7, 2012

Asters, Asters, Asters

An annual workshop offered by the Georgia Botanical Society is called “Aster, Asters, Asters” and it provides hands on learning about members of the Asteraceae family. Look for it every fall on their schedule – I have been twice now and learned just as much the second time. This post, despite having the same name, is about what gardeners call “Asters” – that is, those beautiful fall flowers that look like delicate daisies in the fall but come in shades of white, blue and purple.

Late purple aster, Symphyotrichum patens

Aster is a very convenient name, easy to pronounce and easy to remember. That’s why several years ago the taxonomists decided to change all that. Most of the fall blooming North American asters now reside in the genus Symphyotrichum with a few others scattered into other places (like Eurybia). Apparently DNA studies found that North American plants known as Aster were quite different from Eurasian plants known as Aster. Unfortunately Eurasian asters got to keep the old name! You can read more about the change here.

Asters in the genus Symphyotrichum bloom on wiry stems that probably look like weeds to many folks that have not witnessed their transformation in person. The leaves are either rough in texture or small in size - neither attributes designed to win the hearts of gardeners. However, once their blooms open up and reveal those beautiful flowers - every gardener will be wanting to make a place for them!

Georgia aster, Symphyotrichum georgianum
The beautiful Georgia aster (Symphyotrichum georgianum) is listed as threatened in the state. I feel fortunate to live in an area where it grows naturally. The blooms are the largest and have the deepest shade of purple. The disk flowers in the center start out with a cream color (not yellow like other asters); they age to purple, intensifying the overall purple color of the flower.

Compared to the Georgia aster, late purple aster (Symphyotrichum patens) - shown in the first picture - is slightly smaller, a lighter shade of purple, and has a yellow center. However, the foliage of the two species is very similar; I can't distinguish one from the other unless the plant is blooming.

Eastern silver aster, Symphyotrichum concolor

Another blue aster in my area is the eastern silver aster (Symphyotrichum concolor). The habit of this plant is different from the previous ones. Flower buds are closely held against a long stem as are many small leaves. The effect is quite beautiful when the blooms are open.

Symphyotrichum oblongifolium 'Raydon's Favorite'

New England aster (Symphyotrichum novae-angliae) is listed as native to Georgia but only sparsely; it is much more common in the mid-Atlantic and New England areas. However it is very showy, with large blue-pink blooms; it has been bred by nurserymen into a popular fall plant with a dense floral display. Aromatic aster (Symphyotrichum oblongifolium) and New York aster (Symphyotrichum novi-belgii), which are not native to Georgia, are also showy. I found the cultivar Symphyotrichum oblongifolium 'Raydon's Favorite' at a plant sale this weekend and people were snapping it up. It was also planted in the venue's gardens where it was doing quite well.

Aren't those blue and purple asters pretty?  White asters, however, are the true workhorses of the local aster world. They are the ones popping up in strange places as well as dominating the side of the roads in their season. In fact they are so ubiquitous that people take them for granted. Let's take a few minutes to celebrate their floral awesomeness!

Calico aster, Symphyotrichum lateriflorum
The calico aster (Symphyotrichum lateriflorum) has a lot of character. It has a relatively modest number of flowers, but they put on a colorful show. Like the Georgia aster and others, the disk flowers in the center change color over time and that allows for the different colors. Several cultivars are available including 'Lady in Black' which as burgundy-colored foliage.

Symphyotrichum dumosum
The two white asters vying for the title of "most flowers on a plant" are bushy aster (Symphyotrichum dumosum) and one with the name of "smooth white oldfield aster" (Symphyotrichum racemosum). I've spent many hours with cuttings and a hand lens trying to figure out the difference between some of these roadside asters. Distinguishing characteristics include flower size (in centimeters!), length of petiole, presence of hairs, whether the flowers are predominantly arranged on side of the stem, length and shape of leaves, and the look of the bracts underneath the flower itself.

I have both of these white asters in my garden, and this week, while taking pictures for this, I discovered a third one that is completely different. Maybe they are mutating!

Symphyotrichum racemosum

You can see that the flower arrangement on these two is quite different. A contributing factor is the length of the stem holding the flower. The stem on S. dumosum is long, allowing each flower to stand out as an individual.  The stem on S. racemosum is small so that the flowers appear more as a group, each held close to the branch. The flowers are also all facing in the same direction, presenting a very wand-like form (or a raceme, which explains how it got that species name).

Asters in the genus Eurybia have stems and leaves that are different from Symphyotrichum species in terms of shape and texture (that is, stems are not wiry and leaves are smooth, not rough). I suppose that it one reason why the two groups of aster now reside in different genera.

White wood aster, Eurybia divaricata
The white wood aster (Eurybia divaricata) often blooms earlier in the summer than other asters. The leaves are noticeably larger than the Symphyotrichum asters. Unfortunately this seems to make them tastier to deer so I try to protect mine. This is a pretty common part-shade perennial in my area, often overlooked until it starts to bloom.

Showy aster, Eurybia spectabilis

The other member of this genus in my area is the showy aster, Eurybia spectabilis. The purple blooms are very attractive, and there are often multiple flowers blooming at once. The leaves are quite unlike the white wood aster; they are smooth, dark green and fairly narrow.

If you're looking for some input on asters to choose, I recommend reading this report created by the Mt. Cuba Center based on their garden trials.


  1. Very informative post! "Asters" are one of my favorite fall blooms. I have several including the Georgia Aster, Wood Aster and New England Aster and I always look forward to them. I just picked up more Georgia Asters at the SBG native plant sale this weekend and got them in the ground today. Happy Day!

  2. I been seeing a "new to me" aster in abundance up in Floyd, VA that I haven't seen here in Roanoke-and thanks to your post I now know it's Calico Aster. A very sweet little plant. Asters have to be the most confusing and difficult to get a positive ID on.

  3. Dear Ellen,

    I'm pollination ecologist at UC Davis and I'm finishing up a project testing
    various native plant species for their performance in pollinator habitat restorations across the US. I'm writing to ask permission to use a photo from your website in a fact sheet we are developing for USDA NRCS to recommend the best-performing plants.

    The photo I'm interested in is the photo above of Symphyotrichum racemosum. I am also hoping to crop the photo to fit on the fact sheet so I wanted to ask if that is OK.
    Let me know what you think and if you are ok with me using it, whether/how you'd like me to credit you.

    Thanks very much!

    All the best,

    Kimiora Ward
    UC Davis Entomology Department