Hardy perennials that bloom
Mums are the go-to for fall flowers, but they are often considered annuals to be replanted each year. Alternatively, plant reliable perennial fall flowers once and enjoy them for seasons to come. All are part of the Mount Cuba Collection, a group of plants selected and introduced by the Mount Cuba Center, a botanic garden in Delaware. Known for extensive research on native plants and their effectiveness in gardens, the center has introduced about 20 named perennials over the past few decades.
"With the collection, we're taking a snapshot of the best old introductions you can still get commercially, plus some new highlights," explains Sam Hadley, who manages the Trial Garden at the Mount Cuba Center. These plants—all selected as chance seedlings or games, not hybridized for certain traits—took the top spot in a three-year test assessing their value to gardeners and beneficial insects.
1. 'Gold Standard' Tall Tick (Coreopsis tripteris 'Gold Standard')
"This species has a ton of merit, but 'Gold Standard' makes it accessible to home gardeners with limited space," says Sam. The stout Coreopsis tripteris can reach heights of seven feet or more, and it has been found to fail Mount Cuba's Coreopsis test on its own weight. Meanwhile, the 'Gold Standard' grows five to six feet tall and stands erect. Sam points out that the stem "doesn't need to be Chelsea chopped" to improve its firmness. Blooming in late summer to early fall, it feeds many pollinators and later delights American goldfinches with its seeds.
Growing Tips: Provide it with full sun and moderate humidity. Shallow roots can tolerate rocky and clay soils with tall tick seeds. Like the species, 'Gold Standard' spreads slowly by rhizomes or underground stems, but is not invasive. Zones 3–8.
2. 'Bluebird' Smooth Aster ( Symphyotrichum Lae var. Lae 'Bluebird' )
It was the top performer in Mount Cuba's 2003 to 2005 Aster trial. It heralds fall with pale purple-blue ray flowers that support pollinators, including monarch butterflies that migrate late in the season.
"I grow this at home, and (the flowers) are covered in little bugs," says Sam. The flowers are small, but they occur in profusion on this dense, erect, three- to four-foot-tall plant. "You can cut it to make it more compact, but it's unnecessary," he notes. Diseases can disturb the leaves of the aster, but it remain clean all season.
Growing Tips: Keep this aster in full sun to light shade. (More sun will result in a tighter habit and more flowers.) It adapts to a variety of soil types and humidity and is perfectly happy on the dry side. Zones 4–8.
3. 'Purple Dome' New England Aster (Symphyotrichum novae-angliae 'Purple Dome')
The second aster in the Mount Cuba collection displays dark purple flowers on an elegant mound 18 to 24 inches tall. Its compact form pulls double duty: first, it makes this aster ideal for the front of a border or a container; Second, it "overlooks any foliar problems," Sam explains. (This plant can develop powdery mildew in the fall.) He also notes that the hardy and native 'Purple Dome' "reminds me of garden mums, but much better." Favorite partner? Goldenrod, for color mixing.
Growing Tips: Like 'Bluebird', 'Purple Dome' can tolerate full sun or dappled shade and a range of soil types. However, it grows best with consistent humidity, a key difference comparing the natural habitats of different species of the two asters. Zones 3–8.
4. ‘Golden Fleece’ autumn goldenrod (Solidago sphacelata ‘Golden Fleece’)
When we hear "goldenrod," many of us picture tall, skinny wands weaving between similarly tall meadow plants in a natural setting or manicured lawn. The cultivar 'Golden Fleece' "fills a fun niche for goldenrods," says Sam. "It's a dwarf, clump-forming form of this species."
Spreading just 18 to 24 inches tall and 24 to 36 inches wide, it blends well into a mixed bed, with tall edging alLatu can act as a weed-choking ground cover or fill a large container. It blends equally well into formal and natural spaces and finds its autumn blooms "absolutely swarming" with pollinators, in Sam's words. The variety won Europe's International Stodden-Union Award for Best New Plant when it was introduced and is still going strong.
Growing Tips: Sam notes that this goldenrod will last through a "wide range of conditions." It can take partial shade and dry soil but does best in full sun with regular moisture and decent dirt. Zones 4–9.