Long Blooming Perennials: A Toronto Master Gardeners Guide

 

A white form of Echinacea, a long-blooming summer perennial. (Photo: Helen Battersby)

Perennials are plants that renew themselves each year from their hardy roots. Although there are woody perennials, such as trees and shrubs, the plants most people refer to as perennials are herbaceous plants that die back to the ground at the end of the growing season and emerge the following spring to grow and bloom.

Perennials are playing an increasing role in our gardens, often taking over from mass plantings of annuals in both private gardens and public spaces. They offer excellent value as you only have to plant them once for years of enjoyment. Perennials provide an amazing variety of both flowers and foliage. There is a range of sizes to suit any site. Perennial plants add drama to the garden in every season. From early spring to late fall they continually change the appearance of the garden as different plants come into bloom. In winter, those with decorative seed heads or a lasting framework continue to provide interest.

Each year, nurseries offer dozens of new cultivars, many of them bred for longer bloom periods, repeat blooming and disease resistance. Wonderful colour combinations can be achieved by choosing perennials that bloom at the same time. For example, Rudbeckia ‘Goldsturm’ and Sedum ‘Autumn Joy’ is a popular gold and dusty rose combination for fall gardens. And do not overlook the importance of foliage in the garden. It can provide texture and colour throughout the growing season. The foliage of some perennials, such as Dianthus (Pinks), Bergenia, and Heuchera (Coral Bells) is evergreen, adding winter interest to the garden as well.

Characteristics of Long Blooming Perennials

On average, most perennials bloom once per season for a period of one to four weeks. Long blooming perennials can flower for weeks or even months, providing colour with a minimum amount of maintenance. In this fact sheet, plants have been chosen which bloom for at least four weeks and provide attractive foliage when not in flower. In some cases the remaining seed heads are also decorative and may provide food for birds.

A second category of long blooming perennials is those that will bloom a second time when deadheaded after the initial bloom period. Examples of this are some Daylilies (e.g. Happy Returns) and Foxgloves (e.g. Digitalis grandiflora ‘Carillon’). Some perennials have beautiful foliage which can rival the bloom and they offer the added bonus of providing season long interest. One show-stopper whose foliage overtakes the modest bloom is Fallopia japonica ‘Variegata’ (Mountain Fleece-Flower). This plant does not self-seed and is not invasive.

Given soil that does not dry out, Corydalis lutea can bloom from spring through frost. (Photo: Helen Battersby).

Within a genus (family) of plants it is important to realize that not all species or cultivars have the same long blooming habit. For example, many perennial geraniums bloom for a couple of weeks in the garden. In contrast, Geranium ‘Rozanne,’ blooms from late June until frost. Before choosing other cultivars from the same genus, check the plant label for period of bloom or consult one of the references listed below.

Also check for new cultivars that have been propagated for disease and pest resistance. Phlox ‘David’ has mildew resistance and the thicker leaved hostas resist slugs. Make sure that the plant is hardy to your zone. Plants that are rated for zone 6 and lower are hardy in Toronto gardens.

Cultural Conditions

No matter what your garden soil or light conditions, there will be perennial plants that can thrive in them. It is important to choose plants that match your growing conditions in order to minimize maintenance and maximize plant performance. Although some perennials thrive under hot, dry conditions, keep in mind that most perennials do best with one inch of water per week. Many perennials do fine in average well-drained soil. Improving the soil before planting, by adding organic material (e.g. compost, manure, leaf mould, or peat moss), will ensure that your perennials perform well for years. It will also allow for a wider variety of plant choices.

Perennials thrive in a wide variety of conditions from shade to full sun and bloom at various times throughout the growing season. Suggestions for each season and light condition are included below. Full sun indicates that plants require at least 6 hours of direct, late-morning or afternoon sun. Partial shade assumes that plants require a minimum of 4 hours of morning or afternoon sun but should be shaded from the hot, midday sun. Full shade plants are those that can thrive with less than 4 hours of sun. A bright location that receives no direct sun would be classified as full shade.

Uses

Long blooming perennials are often excellent choices for a mixed border where trees, shrubs, evergreens, flowering bulbs, annuals, grasses, wildflowers, herbs and perennials are combined in one planting border to create a pleasing design. In this way, colour and interest is provided for all four seasons, including our Canadian winter. Plan to include spring blooming perennials with spring bulbs and flowering shrubs, and fall blooming perennials with ornamental grasses.

Many long blooming perennials also make a great addition to mixed container plantings. If you plan to attempt to over-winter the perennial in the container, then select plants at least two zones hardier than ours (Toronto is zone 6).

General Care and Maintenance

Proper soil preparation is the single most important step in creating a beautiful, healthy perennial garden. Dry sandy soils benefit from the addition of organic matter, such as compost, moistened peat moss or composted manure. Add a 4-6” layer of organic matter plus a 2” layer of course grit to open up clay soils. Spread the amendments on top of your planting area, allowing existing microorganisms in the soil to incorporate the material over time as needed. This ensures that the soil profile is not disturbed.

Slow-release organic fertilizers, like bone or blood meal, or granular fertilizers are best added when soils are being prepared. Soils should be weed free before planting.

Using a product containing mycorrhizal fungi (a fungus that occurs naturally in the soil) at planting time, will enhance the development of the roots, reduce transplant shock, and result in a sturdier, healthier plant.

A 2-3” layer of organic mulch will keep the soil cool and moist, reduce water requirements and lessen weed germination. As well, it improves soil structure and feeds the plants when it breaks down. Shredded bark, compost, and pine needles make good mulches.

Newly planted perennials, even those that are drought tolerant once established, need to be watered at planting time. Then, water every week for the first two weeks and during periods of drought. Most borders thrive best with a minimum of one inch of water per week. Monitor and pull out weeds as they germinate and while still young to prevent them from setting seed.

Deadhead perennials to prolong bloom or, alternatively, allow attractive seed heads to stand over the winter. Tidy up the plants in the fall by removing unsightly foliage. During spring cleanup flowers stalks should be cut just above the ground.

Sedum spectabilis ‘Autumn Joy’ lives up to its name in late-summer/early-fall. The dried flower heads also add a sculptural element in the first snows. (Photo: Helen Battersby)

Pests and Diseases

Monitor your plants from week to week for problems. For aphids and spider mites, spray with water. This is a safe way to handle many garden pests and diseases. Always dispose of diseased foliage in the garbage, not the composter. The species listed below have been chosen for pest and disease resistance.

Long Blooming Perennials for Spring

Corydalis lutea (Golden Corydalis) With fern like foliage and little yellow flowers, this plant has an unusually long bloom period from May to September. It prefers a moist, well-drained soil, and part shade. But it will do just fine in the dry rooty shade of a Norway Maple. Although it self seeds, seedlings are easily removed. Hardy to zone 3. (12” x 12”)

Dianthus gratianopolitanus ‘Firewitch’ (Cheddar Pink). This plants blooms heavily in late spring, sporadically through the summer, and often re-blooms in the fall, particularly when consistently deadheaded. Only 8” tall and 18-23” in diameter, this is an excellent plant, for edging, rock gardens, for use as a groundcover, or in containers. Dianthus grows best in loose, well-drained soil in full sun, tolerates light shade in the afternoon, but needs regular watering through periods of drought. Hardy to zone 3. Perennial Plant of the Year, 2006 (8” tall x 23” wide)

Dicentra formosa ‘Luxuriant’ (Fern-leaved Bleedingheart). This plant is a little workhorse for the spring and summer garden. It has beautiful blue-green lacy foliage with pink flowers. It blooms from May to August, in part shade or shade, and requires only a well-drained soil. Hardy to zone 2. (12” x 18”)

Doronicum orientale ‘Magnificum’ (Leopard’s Bane) These yellow daisies bloom for 3-4 weeks in May, in sun or part shade. They prefer average to moist well-drained soil, and are tolerant of woodland conditions. Hardy to zone 2. (18” tall x 12” wide)

Nepeta racemosa ‘Walker’s Low’ (Blue Catmint). This is a good edging plant that is drought tolerant, requiring only average soil and full sun. It blooms from April to October with mounds of lavender blue flowers. It is important to deadhead after the first flush of bloom to keep it blooming all season. Hardy to zone 3. Perennial plant of the year, 2007. (12” tall x 18” wide)

Pulmonaria ‘Sissinghurst White’ (Lungwort) prefers rich, moist, well-drained soil, in part shade or shade. This hybrid has white flowers with silver spotted light green foliage. It blooms for about four to six weeks starting in late April. After blooming, deadhead the flower stems and remove any tired foliage to encourage a fresh burst of new leaves. Hardy to zone 3. (12” x 16”)

Tiarella ‘Spring Symphony’ (Foamflower) has purple-black veining in the leaves, which turn bronze purple over the winter, and soft pink flower spikes from May to July. It prefers rich moist well-drained soil in part shade or shade. This plant is a clumper and not invasive. Hardy to zone 4. (10” x 12”)

Long Blooming Perennials for Summer

Calamintha nepeta subsp. nepeta (Dwarf Calamint) This plant qualifies as a great filler plant or border edger. It blooms from July to October with short spikes of pale lilac flowers that attract bees and butterflies, and the foliage is fragrant. It requires average to moist well-drained soil in sun or part shade. Hardy to zone 4. (12” x 18”)

Coreopsis verticillata ‘Moonbeam’ (Thread-leaved Moonbeam Coreopsis) Although this plant emerges late in the spring, it blooms from June to September with pale yellow flowers and narrow threadlike leaves. It is excellent for mass planting, tolerates a wide range of soil conditions, and is very drought-tolerant. Plan to divide every two to three years to retain a vigorous plant. Hardy to zone 4. Perennial Plant of the Year,1992, and an all-time favourite. (18” x 18”)

Echinacea purpurea ‘White Swan’ (White Coneflower) Coneflowers require good drainage and prefer full sun, but will tolerate partial shade. They are drought tolerant and attract birds and butterflies. They bloom from July to September. Deadheading will prolong the bloom period. Any remaining seed heads will attract birds over the winter. ‘White Swan’ has a distinctive flower, with white petals that droop around a central greenish-brown cone. (36” x 18”)

Eryngium planum ‘Sapphire Blue’ (Sea Holly) This plant has a striking flower with long prickly blue bracts around a central cone. It requires dry, sandy soil in full sun. It blooms from June to August. Plants are taprooted and resent being moved. Plants should be cut down in the fall when the seed heads have turned brown. Leave the rosette of foliage at the base of the plant which is evergreen over the winter. Hardy to zone 4 (30” x 24”)

Geranium ‘Rozanne’. Beautiful violet-blue blooms from late June to frost, in sun or part shade. G.‘Rozanne’ requires average to moist, well-drained soil. It performs well in borders, as an edging plant, or in containers. It continues to bloom even without deadheading. Hardy to zone 4. Perennial Plant of the Year, 2008. (18” x 24”)

Heliopsis helianthoides ‘Lorraine Sunshine’ (False Sunflower) This plant has beautiful green and white variegated foliage all season long, and yellow daisy flowers from June to October. It prefers moist, well-drained soil and full sun. Hardy to zone 2. (3’ x 2’)

Hemerocallis ‘Siloam Amazing Grace’ (Daylily) This is one of the newer daylilies, that have been bred for double the normal bloom period, a minimum of 42 days (late June to mid July) with good disease resistance and superior foliage. It has large ruffled bright-yellow flowers. Daylilies prefer a moist rich soil, but will tolerate a wide variety of conditions. Hardy to zone 2.

Tradescantia x andersoniana ‘Concord Grape’ (Spiderwort) It forms an attractive clump of blue-green grassy leaves with bright purple flowers from June to September. It performs well in both sun or part shade, prefers moist well-drained soil. Plants should be sheared back after flowering to tidy up the plant and encourage repeat blooming. Hardy to zone 3. (16” x18”)

Long Blooming Perennials for Fall

Actea (syn. Cimicifuga) simplex ‘Brunette’ (Bugbane) This is a superb plant for late season bloom, with bronze purple clumps of lacy foliage, and a spike of pale pink fragrant flowers, growing 5-6 feet tall. It prefers rich moist soil in sun or part shade. The foliage of A.‘Hillside Black Beauty’ is slightly darker than A.‘Brunette’. Hardy to zone 3. (5’ x 2’)

Aster x frikartii ‘Monch’ (Frikart’s Aster) This is a hybrid Aster that blooms profusely from July to October with beautiful, large, lilac daisy flowers. It is mildew resistant, and requires average well-drained soil in full sun. It is recommended that it be planted before midsummer and it requires good drainage over winter. Pinch back in May or June to keep the plant compact and to promote additional buds. Hardy to zone 5. (24” x 24”)

Eupatorium rugosum ‘Chocolate’ (Boneset) This plant has been chosen as it blooms very late in the season, often starting in late September and continuing into November. It has beautiful bronze-purple foliage all season and white flowers. It prefers average to moist well-drained soil in sun or part shade, but will tolerate dry shade. Hardy to zone 5. (36” x 36”)

Fallopia japonica ‘Variegata’ (Mountain Fleece-Flower) This is a wonderful foliage plant with green heart-shaped leaves which are splashed with irregular blotches of creamy–white. Stems are pink and new growth emerges a coral colour. Fragrant white blooms in September to October. This is a great ornamental for part to full shade, in moist, well-drained soil. It does not self seed. Hardy to zone 5. (36” x 24”)

Rudbeckia fulgida ‘Goldsturm’ (Orange Coneflower) This is a beautiful black eyed Susan for full sun with a long bloom period from July to October. R. ‘Goldsturm’ has been rated as one of the best perennials of all time. This is a sturdy plant with golden-orange daisies and a dark brown eye. It requires average or moist well-drained soil. Clumps are easily divided in spring and will self-seed around the garden to some extent, usually to good effect. Hardy to zone 3. Perennial Plant of the Year, 1999. (30” x 24”)

Sedum ‘Autumn Joy’ (Stonecrop) The taller Sedums are great garden performers and S. ‘Autumn Joy’ looks good in all four seasons. Its flower buds are attractive long before they are fully in bloom, as they gradually turn from white to rose, and the seed heads are sturdy and attractive all winter long, so no need to deadhead. An added bonus is that the Monarch butterflies favour this plant for nectar. It does best in average, well-drained soil and full sun, but will tolerate partial shade. It blooms for many weeks throughout September and October. It is good for mass planting and is considered to be one of the top ten best performing perennials. Hardy to zone 2. (2’ x 2’)

Tricyrtis ‘Togen’ (Toad-lily) Toad-lilies are shade tolerant and one of the latest plants to bloom in the fall. Plant them up front so you can admire the little orchid like flowers. ‘Togen’ is a hybrid and one of the earliest and showiest forms to bloom, beginning in September and continuing into November. Flowers are pale lavender with a purple edge and white centre. They prefer a rich moist soil in shade or part shade, but will tolerate average soil and even dry shade. Dividing plants every 3-4 years will keep plants vigorous. Hardy to zone 4. (2-3’ x 24”)

References

Valleau, John. Perennial Gardening Guide. Abbotsford, British Columbia: Valleybrook International Ventures Inc., 2003.

DiSabato-Aust, Tracy. The Well-Tended Perennial Garden, Planting and Pruning Techniques. Portland, Oregon: Timber Press, 1998

Heritage Perennials http://www.perennials.com

Date revised: January 2012

For printable version, click:  Long Blooming Perennials – A Toronto Master Gardeners Guide

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