During September and October many gardeners are already anticipating spring. Many of us cheerfully labour in our gardens on crisp autumn days, planting colourful tulips, dainty crocuses, and cheerful daffodils to ensure early spring colour next year.
However, spring flowers are not the only way to extend the growing season. It's also possible to have plenty of colour in prairie gardens in September and October. If your garden seems a bit drab right now, think about making a few additions to brighten it next autumn.
Fall-blooming perennials are now taking centre stage in the flower border. Hardy and reliable, fall asters can withstand a few degrees of frost and often bloom through October. Asters produce daisy-like flowers in a large colour range, including white, pink, and purple. Plant asters in a sunny location; they prefer moist, yet well-drained soil.
There are many excellent cultivars, some low-growing, and some reaching 1.5 m in height. Try the compact cushion aster hybrids Aster x dumosus 'Audrey' (lavender blue), 'Alert' (crimson red), 'Little Pink Beauty' (bright pink), and 'Professor Kippenberg' (bright blue). Some popular taller asters include A. novae-angliae 'Alma Potschke' (rose-pink), 'Hella Lacey' (pink), 'September Ruby' (red), and 'Purple Dome' (purple). In addition, look for A. novi-belgii 'Coombe Rosemary' (violet-purple), and 'Winston Churchill' (deep red). The single drawback to late-blooming asters is that they may not bloom in years of exceptionally early hard frost.
The garden mum (Chrysanthemum x morifolium) is another essential fall-blooming perennial with aromatic leaves and masses of flowers. Plant garden mums in full sun or partial shade in rich, well-drained soil and water frequently. The Morden mums are the hardiest for prairie gardens and will bloom from late summer through fall. Choose from 'Morden Canary' (bright yellow), 'Morden Everest' (pure white), 'Morden Gaiety' (bronze), 'Morden Fiesta' (rosy-purple), and others. Other fine chrysanthemums include C. x rubellum 'Clara Curtis' (rose-pink), 'Mary Stoker' (pale apricot), 'Duchess of Edinburgh' (muted red), 'Pink Procession' (soft pink), and 'Paul Boissier' (white).
If you are looking for perennials to bring fall colour to sunny rock gardens, there are many species of sedums, also known as stonecrops, which thrive on the prairies. Sedums have attractive, succulent foliage that enhances the garden throughout the growing season. You can find sedums with red, bronze, purple, variegated, and colourfully edged leaves, in addition to many shades of green. Late-blooming varieties are ideal for the fall garden. The hybrid 'Autumn Joy' produces clusters of flowers that change from green to pink to rust, while 'Vera Jameson' has striking purple leaves and pink flowers. Showy stonecrops (S. spectabile) such as 'Variegatum' and 'Brilliant' bloom in late summer.
Many other perennials will bloom through September and sometimes well into October. Blanketflowers (Gaillardia aristata) produce bronze-centred flowers tipped with yellow. For small areas choose 'Goblin', a dwarf cultivar. Black-eyed Susan (Rudbeckia fulgida) has long-lasting golden yellow flowers with black centres; 'Goldsturm' is a compact and vigorous variety. Many gardeners enjoy the large double yellow daisies of the giant Rudbeckia lacinata 'Golden Glow' up until hard frost. There are many late-blooming yellow daisy-like perennials, such as coreopsis, and golden Marguerites.
The blooms of Helenium autumnale hybrids appear from late July through late September and feature yellow petals, or a combination of orange, bronze, reddish-brown, and crimson petals around a darker centre. Purple coneflower (Echinacea purpurea) is another hardy perennial that will bloom into October. The daisy flowers have deep purple, pink, or white petals that flare downward from bristly, cone-shaped centres. All these perennials prefer a sunny location.
Flowering plants are not the only way to brighten the fall garden. Plan your garden to include a selection of perennials with beautiful foliage all season long, as well as those that change to autumn hues. Silver-leafed perennials (artemisia, lamb's ears) are striking in fall, as are plants with purple foliage (Heuchera micrantha 'Palace Purple').
Some perennials that provide spring or summer bloom have attractive fall foliage colour. Bergenia (Bergenia cordifolia and B. crassifolia) has large, leathery leaves that turn scarlet, then purple as the season progresses. The foliage of many cranesbills (Geranium spp.) and cushion spurge (Euphorbia polychroma) also turns red in the fall.
Plants with attractive seed heads bring texture and interesting shapes to late summer and fall gardens, and may also attract birds. A few good choices are ornamental grasses, alliums, thistles (the cultivated varieties, not the weeds), fuller's teasel (Dipsacus fullonum), and pincushion flowers (Scabiosa caucasica).
Trees and shrubs can introduce lovely yellow, red, purple, or orange fall foliage to the garden. Mountain ash (Sorbus spp.), Ohio buckeye (Aesculus glabra), Amur maple (Acer tataricum var. ginnala), 'Fallgold' black ash (Fraxinus nigra), and trembling aspen (Populus tremuloides) are among the trees that provide the spectacular flaming colours associated with autumn. Good shrubs for intense fall colour include cotoneaster, burning bush (Euonymus spp.), viburnum, and many spireas (e.g. 'Anthony Waterer').
In addition to splendid fall foliage, many trees and shrubs produce brightly coloured fruit in late summer. Ornamental crabapples (Malus x adstringens cultivars), mountain ash, European red elder (Sambucus racemosa), buffaloberry (Shepherdia argentea), viburnum, shrub roses, and red-twigged dogwoods (Cornus alba, C. sericea) are all excellent choices for prairie gardens.