The calico aster blooms in October as the leaves go through a sequence of color changes. (Adrian Higgins/TWP)

I stumbled across a new phrase recently to describe what's happening in the garden at the moment: the fifth season. The term applies to the way that plants collectively bow out in a carnival of decorative decline. Some, such as the prairie flower known as gayfeather, turn a shade of black that tulip breeders can only dream of; the plumes of feather grass shift from blond to something darker and richer. Some of these plants remain upright and stoic during this transition, others lose their inhibitions by gyrating and leaning as they exchange their greenery for something a little more gaudy. The willow blue star (Amsonia tabernaemontana) in particular wants to play the motley fool.

The withered seed heads of the alpine sea holly are set against the straw-colored clumps of grasses in a garden in Somerset, England. (Adrian Higgins/TWP)

I hear you ask: Isn't this leaf coloration thing called, er, the fall? It is, of course, but we think of trees as providing the autumn show. Gardeners who have become beguiled, as I have, by perennials and grasses have found October to be a moment unlike any other. The more perennials and grasses you use, the more interesting the tapestry becomes below the tree canopy. With close observation, you experience a flow of color that is both autumnal in its yellows and tints of oranges and red, but with hues too that are unexpected. You can find leaves, stems, seed heads and grass blades in such shades as purple, lavender-blue, soft magenta, silver gray and browns that range from orange-tan to a murky chocolate.

Planted under an ornamental grass, the cranesbills begin to turn red as the season winds down. (Adrian Higgins/TWP)

The fifth season also contains perennials that aren't evidently throwing an exit party — they're perfectly green. I'm thinking of ferns, epimediums and leadwort, but there are plenty of other examples. Rear-guard perennials are only now coming into sustained bloom, chief among them asters merrily attracting bees as if it were July. To the many varieties of aster, you could add dahlias, Japanese anemones or salvias. I have the aptly named Hosta tardiflora, which doesn't think about flowering until November.

Grasses form an essential component of the fifth season. I am told it's passe to speak of them as ornamental grasses. This is because so many grass varieties are available, appealing and as essential to the late-season garden as grapes are to wine.

Many of the best originate in North America and, as improved cultivars, work just as beautifully in Europe, where they are heartily embraced, as they are here. I continue to be enchanted by the prairie dropseed. The species is slow to bulk up, but after three or four years it becomes a mounding clump of fine blades maybe two feet high and three across and topped with upright and arching stems of seed heads.

The taller switch grasses offer a more solid column of vertical blades and are crowned with a froth of tiny seed heads. The fine-textured effect is accentuated when they are planted in a group. The blades have a reddish tinge now. Shenandoah is stout and applies lots of rouge. Cloud Nine is a much taller variety, flowering to eight feet and spending autumn in an aura of gold. I might worry about it flopping.

Plants display flowers not for our pleasure but to draw pollinators in a partnership that in October produces the spoils of this effort: the seed heads. The clusters of pods and capsules can seem desiccated and colorless, especially when presented in a ring of withered petals or calyxes.

But even this wizened state has a life of its own, and not just because the seed heads are alive with the germ of the next generation. The black lollipops of the coneflower, so effective at punctuating the veil of grasses, are at least as important in early autumn as they are in early summer, when they begin their flowering. The purple coneflower (Echinacea purpurea) is most often planted, but the horticultural cognoscenti seem to really like Echinacea pallida — Hula Dancer is a favored variety. This coneflower has paler and more narrow petals that hang down noticeably. The effect is of a shuttlecock.

The false indigo, or baptisia, is a shrublike perennial that blooms in late spring but has extraordinary purple-black leaves as it ends the year. It might look morose, but when I saw it paired with a pink aster and a yellow cup plant recently, it stopped me in my tracks.

Other perennials are unpredictably beautiful, like the way the filigree leaves of cranesbills turn a rich red, but only some of them, as others remain green.

The purple-black foliage of the baptisia with the still-blooming aster and cup plant. (Adrian Higgins/TWP)

Coneflowers form black lollipops, here resting on a big bluestem grass that is seeing out the season in its own fashion. (Adrian Higgins/TWP)

Where you live may amplify the effect. Astilbes struggle in hot, humid climates and are a perennial for partial shade and evenly moist soils in the Mid-Atlantic. But in England, where I saw a drift earlier this month, they play in the sun and enter the fifth season full of mature beauty — the flower plumes had aged to cinnamon wands, and the exquisitely divided foliage was turning a coral pink.

But it is not just one element that makes this time of year so enriching — it's the confluence of them all that produces a spectacle greater than the sum of its parts. The period feels different, too. Through the growing season, plants naturally ebb and flow. Now the perennial gardener must deal with the sense of an ending. It's sad, yes, but the beauty is intensified by its air of completion.

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