It’s an accepted truth in the retail nursery industry that most customers only buy plants when they’re in full bloom. It’s not hard to guess, then, why many gardens are lacking in late-season plants. By August, gardeners are a little tuckered out and less likely to visit nurseries, so they never get to know all the wonderful plants that are at their best from September onward.
There are so many impressive late-season garden performers, in fact, that I had trouble whittling the list down to just eight. In the end, it was a bit of a coin toss, and I opted to focus more on plants that are less common or have exceptionally long “peak” periods. The runners-up include the old reliable and ubiquitous black-eyed Susan (Rudbeckia), the late flowering bugbanes such as Cimicifuga ‘Hillside Black Beauty’ (not the native C. racemosa, which starts and finishes flowering earlier), and the native asters (two of which I profiled here).
All of these plants require plenty of sun and well-drained soil, with the exception of turtlehead, which can tolerate light shade and a moist spot in the garden.
As a general design rule of thumb, I like to group plants that peak at the same time near one another in the garden rather than space them out too much. A combination I like a lot starts with a tall pink New England or New York aster such as ‘Alma Potschke’ at the rear. In front of that put a few specimens of burgundy-leaved snakeroot (Eupatorium rugosum ‘Chocolate’—see below). Finally, add Northern sea oats (Chasmanthium latifolium—again, see below) in the foreground. The aster will get “bare legs” as the season progresses, as pretty much all tall asters do, but they’ll be hidden by the bushy foliage of the snakeroot. A pink aster, meanwhile, will bring out the deep purple tones of the snakeroot’s foliage. At the front, the heavy, showy seedheads of the ornamental oats will arch gracefully, dance in the slightest breeze, and slowly turn from green to russet as autumn progresses. With a little thought, I’m sure you’ll find many wonderful combinations using these 8 great late-season plants.
Anemone x hybrida ‘Robustissima’
All of the Japanese anemones are good performers, but I recommend ‘Robustissima’ for the North because of its exceptional hardiness. This plant is late to emerge in spring but quickly produces a dense 2-3’ tall clump of grape leaf-shaped foliage. In August, delicate, naked stems spring up another foot, topped by poetically fragile, shell pink flowers. Although it can be aggressive in some gardens, it’s generally not a problem plant. Spraying with deer repellant is essential since it’s a favorite of the hooved crowd.
Northern sea oats
It’s a mystery to me why this medium-sized, self-supporting, very showy and native grass isn’t more common in our gardens! It looks great next to just about any companion, mixes well with small shrubs such as spireas, and its seed heads are long lasting when harvested and dried for arrangements. Grows 2.5-3’ high and 2’ wide.
The two species of turtlehead native to North America and occasionally used in gardens bloom white or pale pink in the wild, but the much more brightly colored cultivar ‘Hot Lips’ is what you’re more likely to find for sale at nurseries. Turtlehead is notable for its extremely long flowering period and robust, healthy foliage. If grown in shade, it can be lax, but in sun I’ve found it to be entirely self-supporting and a nearly no-care plant for the front of the border.
Dahlias, of course, aren’t cold hardy in New England, but of all the common tender tubers and bulbs, it’s the most rewarding. It’s often thought of as just a fall-blooming plant, but that doesn’t have to be so. I put dahlias in the ground around the second week of May. They generally break ground in late May, just when the threat of frost is passing. If you plant them this way, you’ll have flowers starting in July, and they’ll keep going until hard frost, making dahlias one of the longest blooming plants available. I avoid dahlias with enormous flowers because their stems are prone to breakage from the excessive weight they have to bear. Provide tall dahlias with support, and to successfully overwinter them, pack them in ever-so-slightly damp light soil or another medium (nearly anything, from sphagnum moss to wood shavings, will do) and store them at 40 degrees F in a container that is not completely airtight. I’ve overwintered them in everything from damp basements to dry, heated sheds; they seem less sensitive to humidity than temperature—they do not want to get warm! With a little luck, dahlias can last for many, many years.
Chrysanthemum or Mum
A mum by any other name is still a mum…but these days, it’s more likely to be called Dendranthema. Unless you go out of your way to find unusual varieties, the ones you’re most likely to see are apricot-pink ‘Sheffield’ or its lookalike, ‘Cambodian Queen’. Both are bone hardy and medium sized, making them suitable for most New England gardens. Mums, like asters, get “bare legs” and should be planted behind something lower growing and bushy to look their best. They’ll be dense and less likely to flop if you pinch them once or twice by removing a third of their growth before mid July.
Eupatorium coelestinum, syn. Conoclinium coelestinum
If you’re a lover of blue flowers, you’ll want this. Its stems won’t elongate until well after other plants have put on lots of growth, but be patient—it will become bushy once it gets going, growing 2’ tall and indefinitely wide via a dense mat of spreading roots. Regular division is essential! Its exceptional flower color echoes that of Lobelia siphilitica and Caryopteris x clandonensis.
Eupatorium rugosum, syn. Ageratina altissima
This New England native plant is so dirt common you may have dozens of them growing on your property without even knowing it, but you’ll be amazed at what a bushy, showy plant it becomes when you move it away from the woodland edges where it naturally finds its niche and give it the space and sunlight of a perennial border. Its sprays of small white flowers attract a wide variety of nectar feeders. Although the cultivar ‘Chocolate’ (referring to its burgundy leaves) is more commonly offered for sale in nurseries, the plain green-leaved roadside species is equally beautiful.
Here’s a second moderately sized, self-supporting grass with showy seedheads and absolutely minimal maintenance needs. It’s common in commercial plantings, but home gardeners often ignore it in favor of larger, harder to manage grasses. Fountain grass is the perfect companion for any Sedum spectabile, such as ‘Autumn Joy’. Its mophead shape makes it a natural choice for the “first tier” of the perennial border, where its delicate blades can drape gracefully over the edge between border and path.