Achillea millefolium cultivars (Common yarrow)
Wide variety of perennials bloom in summer and autumn; many have grey or green finely dissected aromatic leaves in a wide range of heights (2' to 4') and colours, including yellow, pink, rose, red and white. Prefers moist, well-drained soil in full sun, but tolerates wide range of soils and conditions. Many cultivars hardy to zone 3. Favourite cultivars include 'Paprika' (a tomato red), 'Moonbeam' (citrus yellow with silvery foliage). Divide in spring. Can be invasive.
Aconitum napellus (Blue Monkshood)
Cool, moist, well-drained, mulched sites. These tall, sturdy perennials do not need staking. 4-5 feet in height. Bloom from late July to frost. Part shade. Good for cutting, but note all parts of this plant are very poisonous.
Agastache foeniculum (Anise Hyssop)
A North American prairie wildflower. To 60 cm (3' to 5') tall with spikes of pale violet or white flowers from July to September. The entire plant has a nice anise (licorice) fragrance and can be used to make teas or jellies. Attracts bees and butterflies, and the flowers can be eaten in salads. Full sun, well-drained soil. Reseeds freely.
An old-fashioned plant, really a self-seeding biennial, that looks like it belongs in a Beatrix Potter book. garden. The two metre (7 foot) upright spikes add vertical interest in the garden. Attractive to bees and butterflies. The single-flowered cultivars have better resistance to leaf rust. Good air circulation helps, too. Full sun, well-drained soil.
Clump-forming biennial or short-lived perennial. Has rich, dark purple-red flowers on dark red stems and is a bee attractant. Imposing, architectural plant. Height: 1 to 2 metres (3 to 6 feet). Zone 4.
Artemisia lactiflora (to 5') or A. ludoviciana (to 30") (Wormwood)
Artemisia lactiflora produces showy plumes of creamy-white flowers August through September. Needs well-drained soil with moisture. About 75 to 150 cm tall in bloom. Zone 5. A. ludoviciana has pale, silvery leaves, is drought-tolerant and can spread quickly (and become invasive) if grown in light, sandy soils. Recommended cultivars include 'Silver Frost', 'Silver King' and 'Valerie Finnis'. Hardy to Zone 3-4.
Aster divaricatus (White Wood Aster) (60 cm - 24 "); Aster x frikartii 'Monch' (70 cm - 28") - lavender-blue flowers; Aster lateriflorus 'Prince' (75 cm - 30") Deep plum foliage; blooms are tiny white stars;Aster novae-angliae 'Adenken an Alma Potschke' (New England Aster) (1.2 m - 4'). Salmon-pink flowers; Aster sedifolius 'Nanus' (Rhone Aster) (45 cm - 18") Blue-purple, lilac, or lilac pink rays with yellow disk florets. This plant is tough, durable and able to withstand heat and drought. These cultivars are improvements that bloom earlier on plants that are more compact. Most bloom from August until frost.
Vigorous perennial with toothed, dark green leaves—coarser in habit than the more common, earlier season Astible arendsii. Pinkish-white flowers. (60 cm - 24"). Other cultivars may have purple-pink or reddish-pink flowers. Plant in full fun or partial shade. Prefers moist, humus-rich soil; will not thrive in alkaline or clay soils that dry out in summer, but tolerates more drought than other astilbes.
Boltonia asteroides 'Snowbank' (Bolton's Aster)
Looks like a white fall blooming aster (only taller and no flopping). (1.5m - 5'). A showy plant with masses of small, white, daisy-like flowers. Unlike some asters, this is not susceptible to mildew on its foliage. Sun or part shade. Zone 4.
Campanula cultivars—many cultivars in this useful family, including carpatica. Deadhead for long bloom.
Campanula lactiflora cultivars (Milky Bellflower)
Partial shade and cool, moist soil (does okay in fairly dense shade in my garden). Large clusters of bell-shaped flowers bloom from June to September. (1.2 to 1.5m - 4 to 5'). 'Loddon Anna' has pale pink blooms.
Campanula x 'Birch Hybrid'
Nodding purple-blue flowers bloom from June to September. Low, spreading plant works well in a rock garden or retaining wall. (10cm - 4") Not invasive.
Cephalaria gigantea (Giant scabious, yellow scabious)
Clump-forming perennial bearing pale, primrose—yellow flowerheads that resemble pincushion plant and float at the top of long, airy stems that do not need staking. Has ferny, deep-green leaves. Divide in spring. Likes fertile, moist, well-drained soil. To 2 metres (8 feet) tall. Zone 3.
Ceratostigma plumbaginoides (Blue Leadwort, Plumbago)
Zone 5. An excellent plant with a brilliant, true blue flower colour blooming from August through October. (9 cm - 3 1/2") The foliage turns maroon as the cool fall weather arrives. Does not like wet feet in winter.
Chelone obliqua (Pink Turtlehead)
The rose pink or purple flowers, top sturdy upright stems with yellow beard, of this North American native. Sun or partial shade, prefers moist to wet soils. (5-20 cm - 2-8") Hardy to Zone 3. Blooms from August to October.
Cimicifuga racemosa (Bugbane or black cohosh or snakeroot)
Cimicifuga simplex 'Brunette' (dark, brown-purple foliage, purple tinted, off-white flowers. Now has new Latin name: Actaea simplex (Atropurpurea group) 'Brunette'.
Astilbe-like foliage and wiry stems hold a bottlebrush-type bloom. Rich, moist soil in sun or partial shade. (1.2 to 2.2 m - 4 to 7')-A woodland setting is best but dislikes the dry shade found under some trees. Zone 3-4.
Clematis tangutica (Golden Clematis, Russian virgin's bower)
Bright yellow bell-shaped flowers from July to September, followed by large, silvery, silky seed heads. (5-6m - 15-20') Tolerates poor soil. Grow as a ground cover or climber. Zone 2. Full sun or partial shade. Blooms on new wood so cut back in early spring to first set of study buds.
Coreopsis cultivars are reliable plants that bloom all season long. Includes Grandiflora.
Clump-forming perennial with mauve-pink flowers, 2.5 cm - 1" across. (Height: 60 cm - 24"). Fertile, well-drained soil, full sun or part shade. Deadhead to promote blooms. Zone 4.
Coreopsis verticillata (Thread-leaved coreopsis or tickseed)
Zone 3. Blooms from June to September if deadheaded. Pretty, dainty flowers and foliage belies the toughness of this plant that can withstand drought and full sun. 'Moonbeam' has pale, citrus yellow flowers. New cultivars include a pale pink (not as tough as 'Moonbeam') and 'Limerock Ruby', a deep, rich red.
Corydalis lutea (Golden corydalis)
This plant loves to grow in the partial shade of rock crevices. (40 cm - 16"). Will self-seed if grown in a partially shaded, cool site. Zone 4. Other Corydalis cultivars are available. Zone 4.
Crocosmia 'Lucifer' (Montbretia)
Brilliant flame-red blooms July through September with gladiolus-like foliage. Stands 1 metre (3 feet) tall and glows when in bloom. Mulch over winter. Hardy to Zone 5-6.