Annuals for Shade: A Toronto Master Gardeners Guide

 

Grown for its beautiful foliage, ‘Henna’ coleus (Solenostemon scutellairoides ‘Henna’) is a tender perennial treated as an annual in our climate. Coleus can be over-wintered indoors, or cuttings of non-woody stems can be rooted, to save the plant from year to year. (Photo: Helen Battersby)

An annual plant is one that completes its life cycle from seed to plant to bloom and back to seed again in one season. Annual flowers are often bright, colourful and very floriferous. In this way, they attract pollinating insects to ensure seed production to complete the cycle. Annual plants put on a long flowering display, lasting weeks or even months. Annual plants range from low plants for ground cover, plants of various heights, and flowering vines. Relatively few flowering annuals do well in shade. Plants recommended for shaded areas perform best in a part or light shade (see Cultural Practices below).

Annuals are classified for our region as the following:

  • Hardy annuals: seeds and seedlings can withstand frost and can be planted in the garden in early spring. Pansies, Sweet Alyssum and Forget-me-nots fit this category.
  • Half-hardy annuals: seeds can be planted outdoors after the soil has warmed up but this usually delays bloom, so these are usually sown indoors six to twelve weeks before the frost-free date for our area. Baby Blue-eyes, fibrous Begonias and Bells of Ireland are in this category.
  • Tender annuals: seeds must be started indoors and not planted outdoors until both soil and air temperatures are warm. Examples include Ageratum, Coleus and Impatiens.
  • Also treated as annuals: tender perennials grown from seed or cuttings, and tender bulbs and tubers. Fuchsias, Caladiums and Tuberous Begonias are three examples.

Cultural Considerations

Siting the plant

A shade garden may be described as one that receives less than six hours of direct sunlight per day. Different annuals will tolerate different degrees of shade. Shade is divided into three categories, with each having either moist or dry soil:

  • Part shade: receives direct sunlight for part of the day and shade for the rest.
  • Light shade: receives shade for most or all of the day, although some sunlight does filter down to ground level, such as under a birch tree.
  • Full shade: areas such as the north side of a house receive no direct sunlight, but may receive light reflected off surrounding areas.
Soil

Good soil will promote the best growing conditions and, therefore, the best flowering. Dry, shady conditions are the most challenging in which to grow flowering plants.

To prepare your garden bed for planting, work three to six inches of organic matter such as compost or composted manure into the soil. This will lighten and improve soil drainage in heavy clay soils, and will improve water retention in sandy soil. Mix some granular fertilizer into the garden bed, choosing one with a higher middle number (phosphorous) to promote blooming and strengthen the roots.

While it is less important for annual plants, it is wise to test your soil to determine the nutrient levels before choosing an appropriate fertilizer. As well, test your soil to determine its pH, which is a measure of the acidity or alkalinity of the soil. A pH below 7 indicates acidity, above 7 indicates alkalinity, and a pH of 7 indicates neutrality. A pH range between 5.5 and 7.5 is beneficial as it allows for sufficient microorganism activity and nutrient availability.

Coleus is available in a variety of leaf shapes and colours. (Photo: Helen Battersby)

Air Circulation

Ensure good air circulation around your plants to help prevent disease, particularly mould, which can weaken plants. Check the estimated width of the plant to determine appropriate spacing in your garden bed. The general rule is six inches between plants. However, some types may be grown closer together to achieve a massed appearance.

 Water

All annuals require watering for at least four weeks after planting to help them become established. Check that the soil is moist at least one inch below the surface, and if not, give the plant additional water. Mulch plants with shredded bark, leaf mold, or compost to retain moisture, to keep the root zone cooler, and to suppress weed seed germination. In dry gardens, rocks buried 2/3 of their height can provide a cooler root run and carry rainwater and irrigation down to the root zone of annuals adjacent to the rocks.

Deadhead

Most annuals will bloom continuously. However, for a continuous display of bloom, it is important to remove the spent blossoms (deadheading) frequently to prevent seed formation.

Sweet alyssum (Lobularia maritima) makes a long-blooming edging plant. (Photo: Helen Battersby)

Annuals for Dry, Light Shade Conditions

Catharanthus roseus (Madagascar Periwinkle, Cape Periwinkle) to 39 inches (1m) in white to dark pink with darker red centre, cultivars of mauve, peach, scarlet. Long flowering season. Tolerates dry and nutrient deficient conditions. Sensitive to over-watering.

Cleome hassleriana (Spider Flower) drought tolerant. Lots of bloom in full sun to partial shade. Self seeds. 36-72 inches (90-180 cm) x 18-36 inches (45-90 cm) in pink, rose, violet or white.

Dracaena indivisa syn. Cordyline indivisia (Spikes) (20-36 inches (50-98 cm) x 15-18 inches (37-46 cm) Architectural plant for dramatic foliage effects.

Lobelia erinus mounding or trailing, under 6 inches (15 cm.) profuse flowering. Blue, pinkish red, white. Partial shade to shade.

Lobularia maritima (Sweet Alyssum) Under 6 inches (15 cm) Pink, rose, mauve, white. Continuous bloom. Attractive to bees and butterflies, resistant to deer. Drought tolerant and fragrant. Direct sow seed.

Senecio cineraria (Dusty Miller) a sub-shrub grown for its dissected silver-gray foliage, up to 2 feet(0.6m) tall, slightly wider spread. Flowers are insignificant. Charming in a moonlit garden.

 Annuals for Partial and Light Shade

Another dramatic foliage plant, Caladium hortulanum, also called elephant ears, is a tropical tuber often treated as an annual. (Photo: Helen Battersby)

Ageratum (Floss flower) 6-8 inches (15-20 cm) Fluffy flowers of lavender-blue, white and rose. Compact bedding plant.

Caladium hortulanum (Elephants ears) is a tender tuber grown as an annual. It has variegated colourful foliage up to 15 inches tall (37 cm). Lift the tuber and over-winter indoors.

Consolida ambigua (Larkspur) 18-24 inches (45-60 cm) pink, mauve, light- mediium- dark- violet-blue, purple, white. Easy from seed. Attractive to birds, insects. Self seeds.

Cynoglossum amabile (Chinese forget-me-not) 12-18 inches (30-45 cm) bright blue small flowers bloom until frost.

Hypoestes phyllostachya (Polka dot plant) 9-18 inches (22-45 cm) A foliage plant with leaves speckled with red, pink or white dots.

Ipomoea batatas ‘Blackie’ (Sweet potato vine) with burgundy foliage, and I. batatas ‘Margarita’ with chartreuse foliage, 4-10 inches (10-25 cm). Vigorous, trailing, mounded growth. Dig up tubers in fall and over-winter indoors in vermiculite or peat.

Lobelia erinus See dry light shade conditions, above

Lobularia maritima (Sweet alyssum) See dry light shade conditions, above.

Mimulus tigrinus (Monkey flower) 12 inches (30 cm) (M. x hybridus) 10 inches (25 cm) cream, crimson, orange, red, wine, yellow. Free flowering. Prefers rich soil kept fairly moist.

Moluccella laevis (Bells of Ireland) 24 inches (60 cm) An heirloom flower with bell-shaped green bracts all along the branching stems. Blooms mid-summer to frost. A nice filler around more colourful blooms. Self sows.

Nemophila menziesii (Baby Blue-eyes) spring bloom. 4-6 inches (10-15cm) x 8-12 inches (20-30 cm) Low growing, clump-forming plant. Blue, purple or white cup-shaped blooms often spotted or marked. Easy from seed.

Nicotiana sylvestris (Flowering tobacco) 36-48 inches (90-120 cm) Imposing plant, cascading head of white blooms summer to autumn. Heady evening fragrance. Easy from seed.

Creamy yellow nasturtium (Tropaeolum) ‘Milkmaid’ is one of many cultivars of this easy-to-grow annual. (Photo: Helen Battersby)

N. alata (Flowering tobacco) 12-24 inches (30-60 cm) Loose clusters of lime green, red, white, yellow flowers above large leaves. Blooms summer to fall. Low drought tolerance.

Nigella damascena (Love-in-a-mist) 15 inches (35-40 cm) X 3-6 inches (7-15 cm) Vivid blue, also purples, pink, white with airy ferny foliage and attractive seed pods suitable for drying. Seed directly in garden from early spring and repeat sow every 4 weeks for continuous display.

Oxalis ‘Charmed Wine’ (Shamrock) (12-18 inches (30-45 cm) Blush pink blooms and very large plum-coloured shamrock leaves, spring and summer bloom. Prefers moist soil.

Perilla frutescens crispa (Perilla) 18-24 inches (45-60 cm) Foliage plant grown for its aromatic and silky purple foliage. Self seeds abundantly.

Schizanthus x wisetonensis (Poor Man’s orchid, Butterfly flower) 6-12 inches (15-30 cm) Rose, mauve, bright yellow, blue, magenta, white. Large clusters of flowers above fernlike foliage. Blooms spring through summer. Water regularly. Attractive to butterflies and bees.

Solenostemon scutellairoides (Coleus) 12-24 inches (30-60 cm) grown for colourful foliage in a wide range of sizes and colour combinations of burgundy, purple, red, pink, orange, yellow, gold, white and green. Insignificant flowers.

Thunbergia alata (Blackeyed Susan vine) To 6 feet (180 cm) 5-petalled orange blooms with chocolate-purple eye. Trailing or twining vine. Water regularly for best performance.

Torenia fournieri (Wishbone flower) Upright bush 8-12 inches (15 cm) x 6 inches (15-30cm) Pale violet tubular flowers with deep purple blotches and yellow throat. Blooms summer through autumn. Prefers moist but well-drained compost-enriched soil. Deadheading is not necessary, and the seed heads are attractive.

Tropaeolum (Nasturtium) 12 inches (30 cm) Large unique flowers of orange, yellow, white or red with distinctive water lily-like foliage. Upright or trailing. Leaves and flowers can be used in salads. Prefers poor soil to bloom well.

Annuals for Part Shade Moist Conditions

The cheery faces of Viola or pansies brighten a shady corner. (Photo: Helen Battersby)

No flowering annual can tolerate constantly wet roots, however, some can be grown in moist soil such as the edge of ponds and stream banks.

Begonia x tuberhybrida (Tuberous begonia) has camellia-like flowers in a wide colour range from white, yellow, apricot, orange, pink, red. The leaves can also be variegated. Both pendulous and upright forms. Dig up the tuber in fall and over-winter indoors.

Begonia rex-cultorum (Rex begonia) are hybrids grown for their extremely decorative foliage up to 12 inches (30 cm) long. Rex begonias may be over-wintered indoors or by starting new plants from leaf cuttings.

Begonia semperflorens-cultorum (Wax begonia) is fibrous rooted. Small blossoms in pink, red, white with green, bronze or variegated foliage.

Caladium hortulanum (Elephant ears) – see partial /light shade, above.

Fuchsia hybrids come in upright or pendulous forms. A wide range in assorted colours and colour combinations are available, from pink, white, magenta, and purple, and red single flowers. May be over-wintered indoors.

Myosotis dissitiflora (Forget-me-nots) are 6-12 inches tall (15-30 cm), with blue flower clusters late spring and early summer. Self seeds.

Viola wittrockiana (Pansies) up to 9 inches tall (22 cm) early and late bloom best in cool conditions. Self-seeds. Wide range of single and bi-colours.

Annuals for Full Shade

Browallia elata (Browallia) 12-18 inches (30-45 cm) Blue, blue-violet, violet, white. (B. speciosa (major) 18 inches (45 cm) Blue. Both are heavy bloomers.

Impatiens walleriana 6-12 inches (15-30 cm) by up to 12 inches (30 cm) single and double pink, rose, mauve, magenta, red, apricot, orange, purple, pale yellow, white. No need to deadhead.  Note: There is currently an epidemic of downy mildew affecting this species and it should be avoided until a cure is discovered.

Impatiens x hawkeri (New Guinea Impatiens) Flower colour as other impatiens but the foliage is patterned or variegated. 9-36 inches (23-90 cm).

Oxalis ‘Charmed Wine’ (Shamrock) – see partial/light shade conditions, above.

Solenostemon scutellairoides (Coleus) – see partial/light shade, above.

References

Beck, Alison and Kathy Renwald. Annuals for Ontario. Edmonton, Canada: Lone Pine Publishing, 2001.

Hogue, Marjorie Mason. Amazing annuals: more than 300 container and garden plants for summer-long color. Willowdale, Ontario: Firefly Books, 1999.

About.com:Gardening. http://gardening.about.com

How Stuff Works. http://home.howstuffworks.com/annuals-for-full-shade.htm and http://home.howstuffworks.com/annuals-for-part-shade.htm

Date revised: September 5, 2010

For printable version, click  Annuals for Shade- A Toronto Master Gardeners Guide

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