How to grow sweet alyssum
Overview
Sweet alyssum (Lobularia maritima) is a low-growing, herbaceous annual from the Brassicaceae family, prized for its dense clusters of tiny, honey-scented flowers. It is grown primarily as a seasonal gap-filler for borders, containers, and as a living mulch to attract beneficial insects. Key to success is treating it as a cool-season crop in warmer zones and a warm-season crop in cooler areas.
Varieties
- Carpet of Snow — Classic white-flowered variety, very compact, ideal for edging and ground cover.
- Rosie O'Day — Soft rose-pink flowers, slightly taller than white types, good for mixed containers.
- Easter Bonnet Deep Rose — Rich deep rose colour, excellent for hanging baskets and winter colour in temperate zones.
- Snow Princess — Vigorous, heat-tolerant white variety with larger flowers, bred for Australian conditions.
Soil Preparation
Sweet alyssum prefers a neutral to slightly alkaline soil (pH 6.5–7.5) with good drainage. Enrich with well-rotted compost before planting; avoid heavy clay that stays wet. A light application of lime in acidic soils can improve vigour.
Growing Guide
Sow seeds directly into well-drained soil in a sunny position, barely covering them with a fine layer of seed-raising mix. Space plants 15–20 cm apart for a dense carpet effect; closer spacing (10 cm) works for edging. For a continuous display, sow in succession every 3–4 weeks. In subtropical and temperate zones, plant in autumn for winter–spring bloom; in cool zones, plant in spring after frosts. Avoid overwatering—keep soil moist but not waterlogged to prevent root rot.
Sowing
Sow seeds 3 mm deep, 10–15 cm apart, directly in the garden or in punnets. Germination takes 5–10 days at 18–22°C. For best results, surface-sow and keep moist until emergence. Transplant seedlings when they have 4–6 true leaves, spacing 15–20 cm apart.
Care
Feed every 4–6 weeks with a balanced liquid fertiliser (e.g., seaweed or fish emulsion) to sustain flowering. After the first heavy bloom, shear the plant back by one-third to encourage a second flush and prevent legginess. Deadheading is not essential but tidies the display; a light trim with hedge shears works well.
Companion Planting
Plant sweet alyssum near tomatoes, capsicums, and brassicas to attract hoverflies and parasitic wasps that control aphids and caterpillars. Avoid planting near heavy feeders like corn or pumpkins, as alyssum's shallow roots may compete for moisture. It also makes a fine living mulch under taller vegetables such as beans and peas.
Common Pests & Risks
Aphids and flea beetles are the most common pests; aphids cluster on new growth and can be hosed off or controlled with a weak soap spray. Flea beetles cause small holes in leaves—use a fine insect mesh or diatomaceous earth around seedlings. In humid conditions, downy mildew may appear; improve air circulation and avoid overhead watering.
Harvesting
Harvest not usually relevant.
Troubleshooting
Yellowing lower leaves: overwatering or poor drainage—reduce watering and improve soil. Leggy, sparse growth: too much shade or insufficient feeding—move to full sun and feed lightly. Stunted, pale plants: nitrogen deficiency—apply a liquid feed. Flowers stop in hot weather: heat stress—cut back and water well; blooms return when temperatures cool. Flea beetle damage: small holes in leaves—use insect mesh or diatomaceous earth.