“Move the needle away from just pretty, to pretty and ecologically functional.” That’s year-round gardening advice from Ulrich Lorimer, the director of horticulture at Native Plant Trust, America’s oldest plant-conservation organization, formerly known as the New England Wild Flower Society.
Mr. Lorimer’s advice is particularly relevant at the moment, as we head into late summer in a shifting climate. And following it could satisfy a landscape’s diverse constituencies — from gardeners to various animals and insects — who are all focused on one thing: What comes next?
Of course, gardeners want the show — the “pretty” — to continue, but many of us increasingly understand that there are more urgent matters.
“For a lot of insects, birds, other animals, the season of plenty will draw to an end,” Mr. Lorimer said. “There is a frantic push to get as much out of these late resources before they’re gone, whether for those migrating or staying put.”
Asters and goldenrods, closely related groups of native perennials coming into season now through fall, can extend visuals and bolster benefits — as they do at Native Plant Trust’s public 45-acre Garden in the Woods, in Framingham, Mass.
For migratory butterflies like the painted lady and monarch, these plants’ carbohydrate and nectar sources help fuel the trip, he said, while year-round resident insects, including new queen bumble bees, need resources for hibernation: “Beneficial insects like soldier beetles, rove beetles, lady beetles — they all need to fatten up for winter.”
Mr. Lorimer was the curator of the Native Flora Garden at Brooklyn Botanic Garden for 14 years, so he knows the choices of aster and goldenrod species and cultivars are dizzying. After years of “reading the landscape,” as he put it — looking for clues as to what grows where and with what — he offered some insights.
First Things First
Taxonomically, there are almost no native Aster (with a capital A) in North America; aster (with lowercase a) remains the common name for a species-rich genus that taxonomists have re-examined and largely reassigned elsewhere.
Only one native Aster (A. alpinus) remains in North America, writes Carol Gracie in her new book, “Summer Wildflowers of the Northeast,” and it grows in parts of the mountainous West, and in Alaska and Canada. There are still true Aster species in Eurasia, but domestically, gardeners need to practice using Latin names like Symphyotrichum, Eurybia, Doellingeria, Ionactis and Oclemena.
Telling Asters (or Goldenrods) Apart Is Difficult
That’s true even if you’re an expert.
Both asters and goldenrods are part of the aster family, an incredibly diverse group that includes hard-working native perennials like black-eyed Susan (Rudbeckia), coneflower (Echinacea), sunflower (Helianthus), ironweed (Vernonia) and blazing star (Liatris).
They’re sort of like sparrows: You know it’s a sparrow (or an aster or goldenrod), but at first you may not be certain which one.
Two tools on Native Plant Trust’s website can help: the extensive Go Botany database and the newer Garden Plant Finder. Although the site is New England-centric, Go Botany entries include range maps, and many of the plants listed are native far beyond the Northeast.
There Are Asters for Various Conditions
But don’t plant just one. Mr. Lorimer recommends incorporating several kinds of asters (and goldenrods) into your season-extending plans. That way, he said, “besides the range of textures, colors and forms, you also get more ecological functionality.”
The composite flowers, with fertile, central disk florets surrounded by ray flowers that look like petals, are “like a big party bowl,” he said. “Everyone can come enjoy it, because their shapes don’t exclude a lot of insects the way, say, closed gentian or cardinal flower’s long, skinny, tubular flowers do.”
A subtle detail: “When aster flowers have been pollinated, they turn from yellow to a darker color, as a way to signal pollinators to pay attention to the unpollinated flowers.”
Although some species may not work in a garden context, because they seed around aggressively — they may be more desirable in a larger, looser landscape — there are garden-worthy asters for a range of light and soil conditions.
An example: Showy aster (Eurybia spectabilis), a favorite of Mr. Lorimer’s for dry, partial-sun conditions, is slower to spread and shorter, with bigger purple flowers, than seeding-inclined smooth aster (Symphyotrichum laeve).
New England asters (Symphyotrichum novae-angliae) are beautiful, Mr. Lorimer said, “but they seed around, and if they don’t have friends to lean on they can be rather floppy — hence the push to breed more compact selections.”
Compact Purple Dome, a selection from Mt. Cuba Center in Delaware, has been an industry stalwart, and a new patented one called Vibrant Dome is even shorter — and hot pink.
For the challenge of dry shade, try white woodland aster (Eurybia divaricata) and heart-leaved aster (Symphyotrichum cordifolium). The heart-leaved aster is also adaptable to sun, and its stout stems stand up under a heavy floral load. “It rarely flops in either light condition,” Mr. Lorimer said.
Eurybia macrophylla, the big-leaf aster, makes a great dry-shade ground cover.
For moist sun, he uses New York aster (Symphyotrichum novi-belgii) or bog aster (Oclemena nemoralis); the New York aster grows to four feet, with large purple flowers, while bog aster is half the height and lilac.
Mr. Lorimer also has a soft spot for Calico aster (Symphyotrichum lateriflorum), a sun or light-shade plant for average soil, with small white flowers.
Want to extend the season even further? Cultivars of the Southeastern species aromatic aster (Symphyotrichum oblongifolium) called October Skies and Raydon’s Favorite “are very well behaved, form a nice mound, and pollinators really like them,” he said.
The Powerhouse Plant Called Solidago, or Goldenrod
The Latin name Solidago translates as “becoming whole,” and when Carl Linnaeus, the Swedish botanist, applied it to the genus in 1753, he was acknowledging the plant’s supposed medicinal qualities. If you see a stand of goldenrod buzzing with life today, you could say they were making a lot of creatures whole.
“It’s their time to shine,” Mr. Lorimer said. “They round out the later end of the growing season, and make for the bulk of the floral resources available to wildlife in autumn.”
Many native bees and other insects depend on goldenrod pollen, served up in individual composite flowers “borne on wands, plumes, flat-topped inflorescences and even zigzag ones that make them very accommodating,” he said.
As Douglas W. Tallamy, a professor of entomology and wildlife ecology at the University of Delaware, writes in “Nature’s Best Hope,” his most recent book: “Across the United States, Solidago is the top-ranked genus in terms of hosting the ecologically valuable caterpillars that feed our breeding birds and fall migrants.”
He calls it “a cornerstone plant for meadow and prairies,” noting that winter-resident birds depend on its seed, as do “voles and mice that feed hawks, owls, weasels, coyotes and foxes.”
Gardeners often skip goldenrod because its bloom coincides with that of ragweed (Ambrosia, also in the aster family). Goldenrod is incorrectly blamed for hay fever, although its pollen is not wind-borne. The spreading reputation of another species, Canada goldenrod (Solidago canadensis), also causes hesitation. “It’s a plant with loads of wildlife value, a pioneer species of old fields and open spaces, but often a bad choice for smaller gardens,” said Mr. Lorimer, who recommended goldenrods that are more clump-forming — or at least less rampant.
Goldenrods are not all gold-flowered (Solidago bicolor, or silver-rod, has white ray flowers), or suited only for sunny fields and meadows. Some hail from open woodlands, rocky clearings and forest edges.
For dry shade, try blue-stemmed or wreath goldenrod (Solidago caesia), or the silver-rod; for moister but well-drained, shady sites, Mr. Lorimer suggested zigzag goldenrod (Solidago flexicaulis).
Licorice-leaved goldenrod (Solidago odora) “plays nicely in sunny gardens,” Mr. Lorimer said. Gray goldenrod (Solidago nemoralis) and early goldenrod (Solidago juncea) are good choices for sunny, dry spots.
Rough-leaved goldenrod (Solidago patula), pine barrens goldenrod (Solidago fistulosa) and wand goldenrod (Solidago stricta) are well matched to a range of sites — from sunny to partial shade — in medium to wet soils.
Native Plant Trust propagates more than 250 types of native plants for sale at its Nasami Farm in Whately, Mass., and also sells them at Garden in the Woods. In other regions, seek out native-plant societies and nurseries. (More on that here.)
Grow the Species or a Named Cultivar?
With native plants, including asters and goldenrods, gardeners often know named varieties better than the species from which those cultivars are derived. Sometimes referred to as nativars, they are often bred for shorter-stature, showier flowers and other traits gardeners favor.
But what do insects, which evolved for thousands of years along with nature’s original species, think of the results of human tinkering?
“We don’t have all the answers for every species, and research is underway, with more needed,” Mr. Lorimer said. “But we do know that changing a plant solely based on aesthetics can have negative impacts on the wildlife it supports, as well as implications for that plant’s ability to adapt in the face of shifts in climate.”
Especially tricky, not in garden performance but in the bigger picture: cultivars or hybrids propagated for sale asexually — by cloning, including division or cuttings, or even in a lab by tissue culture — rather than by seed. This includes all patented plants (their labels say PP followed by a number) and many with non-Latinized names inside single quotes.
Making seed, or reproducing sexually, is nature’s way of keeping a population genetically diverse.
“That has been the process of plant evolution forever,” Mr. Lorimer said. “Now they have to survive a more rapidly changing climate — and with a more limited gene pool to draw from, they may have a harder time adapting.”
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