In the May/June 2018 issue, we got to know some of the plants that grace Mt. Cuba Center’s hot, sunny South Garden during the spring and summer months (“12 Great Natives for a Sunny Border,”). The garden had been recently redesigned to showcase a collection of borderworthy natives that can take the heat of the Zone 7 summers in Hockessin, Delaware.
At season’s end, the carefully planned color palette transitions from the warm pinks and oranges of summer to an explosion of blue, gold, and burgundy. The plant list includes well-known fall favorites as well as a few up-and-coming autumn attractions, such as ‘Summer Sunshine’ coreopsis and ‘October Skies’ aromatic aster. Both top performers in Mt. Cuba Center’s plant trials, they definitely deserve to be grown in more gardens.
By massing several plants of each variety together and repeating these blocks of color throughout the garden, the horticulturists who designed the garden struck a delicate balance. The double borders feel formal but not forced, and each plant has enough space to really show what it can do.
When planning your garden’s fall finale, don’t overlook your region’s native plants. There are many excellent species and cultivars that look perfect in a more formal setting, and your local pollinators and wildlife will appreciate the autumn bounty.
Try these at home
Donna Wiley, horticulturist at Mt. Cuba Center, was on the South Garden’s design team and has tended this collection of heat-tolerant natives since it was planted in 2015. Here are her tips for enjoying these autumn beauties in your own garden.
1. ‘Shenandoah’ switchgrass
(Panicum virgatum ‘Shenandoah’, Zones 5–9)
‘Shenandoah’ has a long season of interest, with attractive foliage that remains upright. It starts to flower in late summer; the airy pink flower spikes turn beige in the fall and persist through winter.
2. Giant coneflower
(Rudbeckia maxima, Zones 4–9)
To encourage more silver-green basal foliage late in the season, cut stems to the ground after the flowers fade, and clean any bad foliage from the base. The new leaves that emerge will look good through fall. Stalks left in place may flop over, but if you have room for them to do their thing, goldfinches will visit often to feast on the seeds.
3. Tiny Wine® Atlantic ninebark
(Physocarpus opulifolius ‘SMPOTW’, Zones 3–8)
The foliage of this shrub provides rich, dark color throughout the season and takes on a reddish tint in fall. Prune it in late spring after it flowers to keep it in scale with the rest of your garden. Its flowers attract plenty of pollinators.
4. Willow-leaved blue star
(Amsonia tabernaemontana var. salicifolia, Zones 3–9)
After spring flowers fade, blue star can be cut back by about half to keep the plant’s habit more full and compact. The foliage stays attractive all season, turning golden yellow in late fall.
5. ‘Summer Sunshine’ coreopsis
(Coreopsis palustris ‘Summer Sunshine’, Zones 6–9)
From late September into October, this low-maintenance plant provides bountiful blooms. It has a sturdy, upright habit and light-green foliage that is disease free. It tolerates full sun, hot weather, and well-drained soil.
6. ‘Dark Towers’ penstemon
(Penstemon ‘Dark Towers’, Zones 3–8)
This dark-leaved plant produces a bounty of attractive burgundy seed pods after its early summer flowers fade. It looks equally nice either cut back to expose the rosette of burgundy foliage or with seed spikes left on for a taller show. Cutting the seed stalks off in late autumn helps the basal foliage toughen up for the winter; it also prevents unwanted seedlings.
7. ‘Concord Grape’ spiderwort
(Tradescantia ‘Concord Grape’, Zones 3–9)
Unless the weather is wet, ‘Concord Grape’ needs supplemental water to get through the heat of summer. Cut stems to the ground in midsummer after flowering starts to slack off, leaving any new foliage emerging at ground level. Fresh foliage will start to grow soon after.
8. ‘Arizona Apricot’ blanket flower
(Gaillardia ‘Arizona Apricot’, Zones 4–9)
This little powerhouse blooms all season long, provided it has excellent drainage and loose soil, not clay. If it is deadheaded as the flowers fade, it can bloom from early summer through late autumn.
9. ‘Bluebird’ smooth blue aster
(Symphyotrichum laeve ‘Bluebird’, Zones 4–8)
This pollinator-pleaser is a Mt. Cuba Center introduction. It shouldn’t be pruned or shaped, because its habit is different from many asters; it produces flower spikes that emerge from basal foliage. Give it plenty of room, and enjoy the show!
10. ‘October Skies’ aromatic aster
(Symphyotrichum oblongifolium ‘October Skies’, Zones 3–8)
The shorter of the two asters grown in the South Garden, ‘October Skies’ (photo p. 65) only grows about 2 feet tall. It may be cut back by about half in June to make it fuller. In fact, most North American asters (Symphyotrichum spp. and cvs., Zones 3–8) may be pruned or shaped before July 4 without reducing their bloom.