Wednesday, September 7, 2011

The Complementary Colors of Fall (Part 1)

Symphyotrichum cordifolium (f/k/a Aster cordifolius)
Blue Heart-leaved Aster /Blue Wood Aster
Anyone who lives in Michigan knows that, if you don't like the weather, just wait; it'll change, for better of worse.  Hard for some folks to believe that, on September 3rd we were huddling in our homes with the air conditioning going, flashing back to the third week of July and two days later, on September 5th, it was definite "sweater weather".  But that's Michigan for you.

So, it looks like Fall really is on its way, and with it the wildflowers of the season.  This is an important time of year for some of our pollinators, as they prepare for winter in their individual ways - all of which feature important end-of-season wildflowers to either prepare them for their long migrations, as in Monarch Butterflies, or storing additional food to carry them through the winter, as in some of our native bees.  It all adds up to just one aspect of our dynamic Fall Show here in the Mitten State, and Mother Nature doesn't stint on her selections.

One of the most important groups of flowering plants for the season are our native Asters.  Many of the names of these plants have been changed to reflect relatively recent genetic studies which led to the discovery that, while our native Asters do belong the Aster Family (Asteraceae, formerly Compositeae), they were found to be sufficiently genetically distinct from the family's name species (Aster amellus, or the Michelmas Daisy) and its Old World allies, that they were assigned to other genera.  In all such cases, the second part of the plant's binomial Latin name (the "epithet") has been retained, although modified if necessary to correspond to the new genus.   (For example, our native Blue Heart-leaved or Blue Wood Aster, formerly known as "Aster cordifolius", is now known as "Symphyotrichum cordifolium".)  The good news is that many growers and print sources are retaining the plants' old names, as well their new ones, in their publications to ease us through this difficult transition.  So, just because it isn't called an Aster any more, does not mean it isn't an Aster!

Symphyotrichum laevum (f/k/a Aster laevis)
Smooth Blue Aster
Our Asters, like the rest of the family, are characterized by composite flowers consisting of "ray flowers", which are at the edge of the efflorescence and have long, narrow, showy petals, and "disk flowers" which make up the center of the flower.  The ray flowers are sterile, but act as "flags" for potential pollinators to draw them into nectar on, and pollinate, the numerous disk flowers (think about the seed head on a big sunflower, another member of the Aster Family, and you'll get the idea), which is why many pollinators spend a lot of time on a single flowerhead, nectaring on - and pollinating -  every flower, leading to very high seed production.  Many of the markings on these petals are only visible in the ultraviolet range of light - invisible to us but within an insect's visual field, acting as flags to guide them into the bounty at the flower's center. Also typical of Old World Asters, flower color tends to the cool white/blue/lavender range.

Blue Heart-leaved, or Blue Wood, Aster, (Symphyotrichum cordifolium, f/k/a Aster cordifolius) is a relatively small, conservative plant with, yes, heart-shaped basal leaves ("cordi-" means "heart-shaped).  The plant sends out graceful, arching stems up to three feet tall topped with clusters of small, delicate flowers of a very pale violet, almost white, which makes it a lovely addition to the front of the border.  True to one of its common names, this is not necessarily a plant for full sun; as an added bonus, it can handle dry shade, one of the more challenging combinations of conditions in some of our gardens.  With the light flower color, it really shines in a woodland setting.

Smooth Blue Aster (Symphyotrichum laevum, f/k/a Aster laevis) is, over time, a more massive plant that can benefit from division and sharing.  It likes a bit more sun than Blue Heart-leaved Aster but does well in drier conditions, being quite drought tolerant.  The pale violet flowers form a loose panicle at the top of graceful, three-foot stems, emerging from long, tapered, blue-gray basal foliage.  The stems are denser, as the leaves, gradually reduced in size, also clothe the flower stems.  With a neat habit, as long as it gets the sun it wants, it won't need any staking and looks lovely in a mass planting.

Symphyotrichum novae-angliae (f/k/a Aster novae-angliae)
New England Aster
New England Aster (Symphyotrichum novae-angliae, f/k/a Aster novae-angliae) is probably the best-known of our native species.  This is a tall, charismatic, relatively massive plant which works well in the back of the border or in the center of a large bed.  In masses it is truly impressive, with its relatively dark violet-to-purple flowers, especially in context with many of the yellow-flowering plants of the season; it can top out at five to six feet, and may benefit from staking as it can bend under the weight of the flowers.  If you would prefer shorter, fuller plants, however, you can cut them down by a third at the beginning of June, July and August, to encourage denser shorter growth with greater flower production, like the ever-popular Fall-blooming garden mum, also a member of Asteraceae.  Not surprisingly, this species prefers moister conditions to really thrive, forming a thick clump after a few years.  It is certainly one of the showiest species - literally covered with blooms - and pollinators - at its peak.

As a precaution, bunnies and deer love members of the Asteraceae family.  I took a late walk to my garage from my house last night, and my resident rabbit was out sampling a nearly-midnight snack.   I'm sure he has the most educated palette in all of Detroit by now, at least in terms of native plants, because he's tried everything in my garden!

All photos by Don Schulte,