What are the sun requirements for Matthiola bicornis?

Matthiola bicornis (syn. M. longipetala subsp. bicornis) is a hardy annual in the mustard family (Brassicaceae) grown primarily for an intense evening fragrance. Plants reach 12-18 inches (30-45 cm) tall and 6-8 inches (15-20 cm) wide with a slender, upright to somewhat lax habit. Stems are branching and covered in short grey-green hairs. Leaves are narrow-lanceolate, 2-4 inches (5-10 cm) long, grey-green, with slightly wavy or toothed margins. Flowers are small, four-petalled, 0.5-0.75 inch (12-18 mm) across, in shades of mauve, lilac, pink, or white — visually inconspicuous during the day, when petals stay partially closed and the plant looks wilted. At dusk, the petals open fully and release a powerful sweet, clove-like fragrance that carries 15-20 feet (4.5-6 m) in still air. Fragrance peaks between 8 PM and midnight and fades by morning. Flowers are pollinated by nocturnal hawk moths and other night-flying insects. The species is unrelated in growth form to common stock (M. incana) despite sharing the genus — M. bicornis is a straggly annual while M. incana is a showy bedding plant. Bloom begins 8-10 weeks from sowing and continues for 4-6 weeks. Plants are susceptible to flea beetles, downy mildew, and clubroot (Plasmodiophora brassicae); rotation with non-brassica crops reduces incidence.

Native Range

Matthiola bicornis is native to the eastern Mediterranean region, including Greece, Turkey, and southwestern Asia, where the species occurs on rocky hillsides, disturbed ground, and coastal habitats at low elevations.

Suggested Uses

Sown near outdoor seating areas, bedroom windows, and along paths where the evening fragrance can be experienced at close range. Interplanting with day-blooming annuals such as Calendula or Nigella masks the untidy daytime appearance. The species grows in containers on balconies and patios — a 6-inch (15 cm) pot holds 3-5 plants. Often broadcast-sown in mixed annual wildflower strips.

How to Identify

Identified by the narrow grey-green leaves, small mauve to lilac four-petalled flowers that look wilted during the day but open at dusk releasing a powerful sweet fragrance, and the slender branching habit. Separated from M. incana (common stock) by the much smaller flowers, lax habit, and exclusively nocturnal fragrance. The seed pod has two small horns at the tip — the basis for the epithet bicornis.

Appearance

Size & Dimensions

Height1' - 1'6"

Width/Spread6" - 8"

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~5 weeks

Summer

Flowers open from late June through August depending on sowing date. Petals stay partially closed and inconspicuous during daylight. At dusk (approximately 7-9 PM depending on season), petals unfurl fully and fragrance is released. Individual plants bloom for 4-6 weeks. Succession sowing every 3 weeks extends the fragrant period from June through September.

Detailed Descriptions

Flower Description

Mauve, lilac, pink, or white

Foliage Description

Grey-green

Growing Conditions

Sun Requirements

Full Sun Partial Shade

Requires 4-8 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.0 - 7.5(Neutral)

357912

Soil Types

loam sand chalk

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Seeds are direct-sown on the soil surface in mid to late spring, after the last frost. Seeds are tiny — mixing with sand gives even distribution. Seeds are pressed gently into the soil but not covered, since light aids germination. Germination takes 7-14 days at 55-65°F (13-18°C). Seedlings are thinned to 4-6 inches (10-15 cm) apart. Plants grow in full sun to partial shade in average, well-drained soil with a pH of 6.0-7.5. Watering is moderate; established plants tolerate mild drought. No staking is required, though plants may lean; interplanting with sturdier companions reduces flopping. No fertilising is needed in average soil.

Pruning

No pruning is required. Spent plants are removed after bloom declines and replaced with a later succession sowing. When self-seeding is desired, seed pods are allowed to mature and shatter in place — the species self-sows in open, disturbed ground.