There is little subtlety to maturing fall plant relationships. Cooling autumn air temperatures cause petal and leaf colours to intensify; reds become redder, blues are tinged with purple, and greens are burnished with copper. These vivid colours mark the changing of seasons, a last audacious display before hard frost nips at leaves and blossoms.
The hybrid goldenrod 'Fireworks' puts out arching, golden flower stems and forms a thick clump that stays put and doesn't seed around. Looking more refined than its wilder cousin seen in fields and along roadsides, 'Fireworks' finds a soulmate in the dusty-pink stonecrop Autumn Joy, with its broccoli-like flower heads. This striking partnership is intensified by the garden workhorse 'Goldsturm' black-eyed Susan. As a foil to the vertical lines of these plants, I like the airy and relaxed clumps of pale lilac dwarf calamint and mauve pink 'Herrenhausen' ornamental oregano, which keep flowering until the beginning of November. Silver sage (a biennial) provides a cool contrast to this grouping, with its huge rosettes of velvety, pewter grey leaves. A single specimen of this diva makes an emphatic statement of form and shimmering colour. For a more modest combination, try 'Big Ears' lambs' ears.
Small shrubs with ornamental features partner well with autumn perennials. 'Brilliantissima' red chokeberry makes a clever combination in autumn's perennial borders, with its slim form, deep scarlet foliage and clusters of jet-black berries. The chokeberry offers a blazing backdrop for the tall stalks of deep purple 'Arendsii' monkshood (but remember, it's poisonous if ingested by people or pets). For a similar but scaled-down display, pair the shorter violet-blue 'Bressingham Spire' monkshood with a highbush blueberry, such as 'Northblue', which has bright red autumn foliage. Some of the new barberry selections, such as rose pink 'Rose Glow' or burgundy purple Ruby Carousel, would make fine partners, too.