Now that the late summer garden is beginning to look fuller and more colourful and the days are becoming cooler, it's time to consider adding generous clumps of plants that glow with the hues of the season. "It is a good plan to plant them where at some moment of the day they will catch the sunlight; and it is more effective to plant two or three in a clump than some isolated specimen…to make a bonfire of colour in the rich, mellow days of autumn," wrote Vita Sackville-West of her Sissinghurst Garden. Gardeners like myself, who never purchase one of anything, are especially gratified by such advice.
The second group of late bloomers fills the humid days of August and carries on through to October. Rose of Sharon shrub (Hibiscus syriacus, 2.4 metres, Zone 6) begins its six-week season of bloom—my two favourites being the single-flowered 'Blue Bird' and the double mauve 'Ardens'. In moist corners of partial shade, deep blue monkshood (Aconitum napellus, one metre, Zone 3) sends up its long-lasting, delphinium—like spikes of flowers that are both beautiful and toxic (so keep it away from small children and plant-chewing pets). In the same light I can put a fat clump of turtlehead (Chelone obliqua, 90 cm, Zone 5) in rosy purple. And obedient plant (Physostegia virginiana, 90 cm, Zone 3) must find a place in this corner, with its articulated and adjustable little florets arranged in precise lines up and down its stems. It can be had in lovely clear white, or pink 'Bouquet Rose'—though I'm partial to the deep lilac-pink 'Vivid'. Obedient plant wants to run in moist soil, but this can be an asset in such a charming plant. (If you don't think so, there is a recent, more polite, clumping cultivar to try called 'Miss Manners'.) Two more plants for a moist and shady location, and which look lovely planted near each other, are 'The Rocket' ligularia (Ligularia stenocephala 'The Rocket', 1.2 metres, Zone 5)—with its tall, black-stemmed racemes of brilliant yellow florets and decorative mound of toothed foliage—and the fragrant 'Royal Standard' plantain lily (Hosta x plantaginea 'Royal Standard', 60 cm, Zone 4), with glossy ribbed leaves and large, scented white trumpets in August; or the larger-flowered 'Grandiflora' or its double-flowered cousin, 'Aphrodite'.
Out in sun and well-drained soil is the place for a colourful array of single hollyhocks, beloved in cottage gardens (Alcea rosea syn. Althaea rosea, 1.5 metres, Zone 4), and sneezeweed (Helenium autumnale, 1.2 metres, Zone 4), with daisy-like blooms in rich mahogany red (H. 'Bruno'), golden yellow (H. 'Butterpat') and bronze-red (H. 'Riverton Beauty'). As well, 'Worcester Gold' bluebeard (Caryopteris x clandonensis 'Worcester Gold', 90 cm, Zone 5) is a welcome sight with its chartreuse leaves and misty blue flowers—a small shrub that is treated like a perennial in most of Canada.
All these vibrant colours are softened by the narrow racemes of white flowers of Bowman's (or Culver's) root, (Veronicastrum virginicum 'Album', 1.2 metres, Zone 4) and the plumes of creamy white mugwort (Artemisia lactiflora, 1.2 metres, Zone 5)—taller, more subtle and altogether better behaved than its silvery cousins.
At last it's time for the vivid Michaelmas daisies of autumn—lavender blue 'Mönch' (Aster x frikartii 'Mönch', 76 cm, Zone 6) and 'Andenken an Alma Pötschke' (Aster novae-angliae 'Andenken an Alma Pötschke', 76 centimetres, Zone 5)—which combine splendidly with the entirely respectable hybrid goldenrod (Solidago rugosa) cultivars 'Fireworks' (one metre, Zone 6) and 'Crown of Rays' (76 cm, Zone 5). And nearby are the lightly scented bottlebrush stems of 'White Pearl' autumn snakeroot (Actaea matsumurae syn. Cimicifuga simplex 'White Pearl', 1.2 metres, Zone 4).