Aralia elata (Japanese Angelica Tree)
Large, tropical-looking plant. Spiny trunk and leaves. Large umbel of white blooms in late summer at the top of the shrub, followed by black fruit. Height to 10 m high and wide. Full sun or part shade. May sucker vigorously. Hardy to Zone 4. Shelter from strong winds. Fall colour may be yellow, orange or purple. Likes rich, fertile soil.
Buddleia davidii cultivars 'Black Knight', 'Pink Delight', 'Petite Plum', 'Petite Indigo' and 'Empire Blue'
Has showy, fragrant flowers panicles. Blooms better in moist, well-drained, alkaline soil-prune out spent blooms to encourage flowers. Attracts butterflies and bees. Height ranges from 4-8 feet. Japanese beetle host. Blooms from July to frost. Zone 5.
Caryopteris x clandonensis cultivars (Bluebeard)
Dies to ground each spring and can be treated as a perennial. Beautiful blue-gray foliage and clear blue flowers. Blooms from late July to October on current season's growth. Needs adequate moisture. Height to one metre (3'). Butterfly attractant. Full sun. Cultivars include 'Worcester Gold", which has golden foliage. Zone 5
Cephalanthus occidentalis (Button brush, honey willow, honey balls)
Extremely fragrant, white spiky blooms in July progressing to golfball-shaped seeds in the fall. Ideal for moist sites. Full sun. North American native shrub. (1.5m - 6'). Zone 5.
Clethra alnifolia (Summersweet)
White blooms with a spicy fragrance on current season's growth for 4-6 weeks
from July to mid August. Bee attractant. Bark is scaly or exfoliating in loose, long strips as the shrub ages. Likes moist acidic soil, shade or full sun, tolerant of salt,
pest-free. Suckers to form colonies. Cultivar 'Pink Spires' has pink blooms. Zone 3.
Hibiscus moscheutos (Common Rose Mallow, Swamp Mallow)
Sold as a perennial. Large 20 cm diameter white, pink or crimson blooms in late summer. Woody, upright stems reach 2 metres (6') and should be cut down in the spring. Hardy to zone 5. Full sun, well-drained soil. Tough plant.
Hibiscus syriacus cultivars 'Diana' or 'Aphrodite' (Rose of Sharon)
Woody shrub to 3 metres tall and 2 metres wide. Single or double blooms from late summer to fall. Full sun. Cultivars include 'Diana', with single white blooms, and 'Aphrodite', a deep rose pink with dark red eye. Hardy to zone 5.
Hydrangea arborescens 'Grandiflora' and 'Annabelle'
Long term bloom. Blooms in July but flowers persists into winter-may be dried for arrangements. Full sun or shade. More blooms in full sun. Oakleaf hydrangeas are also worthwhile plants.
Vitex agnus-castus (Chaste Tree)
Large shrub to 2 m high. Palmate-shaped foliage with light violet blooms in racemes at ends of current season's growth. Blooms July to Sept. Hardy to zone 6/7. Bee attractant. Pungent odour when the foliage is crushed.
There are many great annuals that can fill in the gaps in the August border. Here are a few of my favourites.
Borago officinalis (Borage)
Grows to about 2', pretty blue flowers, edible. Self-seeds. Full sun, well-drained soil.
Calendula (Pot Marigold)
Another self-seeding favourite. Flowers are yellow, orange or cream. Nice in herb gardens. Grow 12 to 30" tall. Deadhead for repeat blooms. Full sun, well-drained soil.
Cosmos bipinnatus (Cosmos)
Feathery foliage and pretty, daisy-like flowers, usually white, pink or maroon. Comes into its own in late summer/early autumn. Likes full sun, moist, well-drained soil. Grows to 5' tall.
Nicotiana spp. (Flowering tobacco)
Lovely fragrance at night. The old-fashioned flowering tobacco, N. sylvestris, has white flowers, a big, basal rosette of leaves and grows to 5' tall. Smaller cultivars, such as 'Nikki', are around 18" tall and come in a wide range of colours from lime green to maroon. Likes moist, fertile, well-drained soil, sun or part shade.
The salvia (sage) family has a wide range of worthwhile annual and perennial cultivars. I always plant out a flat of Salvia farinacea 'Victoria Blue'-a tough, great filler plant in beds and in containers with pretty, cobalt-blue flowers. Looks good right through to frost.