Sweet Alyssum

Overview. Sweet alyssum is a low, mat-forming annual that forms spreading mounds covered in dense clusters of tiny, fragrant white flowers. The flowers have a honey scent and draw bees, butterflies and beneficial insects. It works well as an edging, between stepping stones, or in containers. Pink, lavender and purple cultivars are available, and white-flowered types are often the most fragrant. Some pages describe it as a short-lived perennial, but it is usually grown as an annual.

Sowing. Sow seed directly in the garden several weeks before the last frost date in spring. You can also start seed indoors 5 to 6 weeks before the last frost and set out seedlings just before the last frost. Another guide suggests starting seed indoors 6 to 8 weeks before planting outdoors. Seeds sprout in 8 to 10 days at 65 to 70 °F (18 to 21 °C). Seeds need light to germinate. Some guides say not to cover them at all, while others say to cover them only lightly with soil. Transplants can go out after the danger of frost has passed.

Fall sowing. Seed can be sown in August for fall flowers, or in September for flowers into winter.

Site. Plant it in full sun to partial shade with well-drained soil.

Flowering time. Plants usually start flowering 6 to 8 weeks after sowing.

Named varieties. Many hybrids are sterile, are not sold as seed, and grow larger with better heat tolerance. Seedlings from named varieties often have white flowers and are taller than the parent plant.

Water. Water regularly and keep the soil at medium moisture. The plant tolerates drought and dry soil.

Feeding. One guide advises feeding monthly with an all-purpose fertilizer during the growing season. Another advises against heavy feeding, because rich soil encourages leaves over flowers.

Shade. It appreciates some afternoon shade, and it may do better in partial shade in hot climates.

Deadheading and shearing. Deadhead the spent flowers to encourage more blooms. Cut plants back after the first flush of blooms to encourage more flowers. Shear overgrown or leggy plants to promote new blooms.

Drainage and rot. Poor drainage, drowning and poorly drained soil can damage the plant and cause it to decline. Dense growth in wet or crowded plantings may rot.

Disease and pests. It may be affected by downy mildew, stem rot and crown rot. Other listed problems include clubroot, white blister, slugs and flea beetles.

Summer heat. Plants can look ragged in hot weather and revive when it cools. Flowering may stop in summer heat, but the plant can be rejuvenated.

Pets. This plant is listed as non-toxic for cats and dogs.