Sweet Alyssum, <em>Lobularia maritima</em>

Sweet alyssum, Lobularia maritima, is a common annual flower plant. — Sweet alyssum, *Lobularia maritima*, is a common annual flower plant.

Overview of Sweet Alyssum

Lobularia maritima is a mat-forming annual native to the Mediterranean, Canary Islands, and Azores, where it grows along the coast in rocky, sunny areas. This herbaceous annual plant in the mustard family (Brassicaeae) is commonly used as a bedding plant called alyssum or sweet alyssum and is widely available in market packs at nurseries and garden centers in the spring. The common name refers to the genus in which it was formerly classified.

Sweet alyssum can be used as a seaonal ground cover. — Sweet alyssum can be used as a seasonal ground cover.

Sweet alyssum grows 3-9 inches tall with a wider spread. Cotyledons are rounded and bright green, while the first true leaves are longer and narrower. The spreading mounds have well-branched stems covered with small linear leaves. The alternate, gray-green leaves are oval to lanceolate without any indentations. Because it is shallow-rooted, low, and spreading, it makes a good living mulch or seasonal ground cover.

The small flowers are attractive to beneficial insects like this syrphid fly. — The small flowers are attractive to beneficial insects like syrphids.

Flowers are produced through the growing season. Each tiny flower has four petals. Many flowers are clustered together in dense terminal heads (racemes) and the plants may bloom so profusely that the foliage is completely obscured. The flowers have a honey-like fragrance and are very attractive to bees, flower flies, stingless wasps and butterflies. It is a particularly good nectar plant for beneficial insects as those tiny insects due to its abundant flowers and long bloom period. In fact, sweet alyssum is planted in commercial organic lettuce and broccoli fields in California to attract natural enemies as part of an integrated pest management (IPM) plan for aphid control.

The tiny, four-petaled flowers (R) are borne in terminal racemes (C) that cover the plant (L).

Alyssum Clear Crystals Lavendar Shades — Alyssum ‘Clear Crystals Lavender Shades’

The flowers of the species are usually white but occasionally are pink or lavender. Plant breeders have selected and enhanced those rare colors to develop some of the many cultivars. White flowered cultivars tend to be more robust and vigorous, and often more fragrant.

Flowers are followed by flat, oval seedpods. The flower stalk elongates as the seeds ripen. The silicle (a dry pod-like fruit, also sometimes spelled as silicula or silicule) contains two yellowish to brown, oval seeds, separated by a papery white skin.

Alyssum inflorescence (L) with seedpod (middle, top) and oval seeds (R). Each pod half contains one seed (middle, bottom).

This low, spreading plant looks nice spilling out along a walkway.

Landscape use of Sweet Alyssum

Alyssum is used as a bedding plant in annual or mixed borders and in containers. It combines nicely with many other short-statured annuals, such as shorter zinnias and marigolds, annual lobelia, celosia, and snapdragons. It works well as an edging plant, as an airy filler among young perennials, or as a ground cover when planted in masses. It can be overplanted among bulbs such as tulips and daffodils to fill in the area as the spring bloomers go dormant, or underplanted beneath clematis, daylily, or roses where its dense growth helps smother weeds. It is especially nice placed where it can spill over the edge of a container or hanging basket, or where it can cascade down a slope in a rock garden.

Alyssum is frequently used as a filler in containers or to cascade down the planters edge.

Sweet alyssum grows well in full sun in cool climates but may do better in partial shade in hot climates. It needs average, well-drained soil with medium moisture. Although it may reseed, it is best to transplant starts in spring for the best flower display (especially in short growing seasons). Sweet alyssum may reseed, but not aggressively. Typically seedlings from named varieties will have white flowers and be taller than the parent plant.

Propagation of Sweet Alyssum

Sweet alyssum is very easy to grow from seed, either sown directly in the garden or indoors several weeks before the average last frost. Barely cover the seed, as it benefits from light in germination. Transplants that have been hardened off can be placed in the garden a week or two before the average last frost, otherwise tender transplants should be protected until add danger of frost is past. Plants generally start flowering within 6-8 weeks from sowing. Although it will tolerate short dry periods, alyssum does best with consistent moisture. Do not fertilize heavily, as overly fertile soil promote foliar growth over flower production. If plants are too wet or crowded, the dense growth may lead to rotting.

Alyssum will flower more profusely if deadheaded. Overgrown or leggy plants or those with more seedpods than flowers can be sheared back to improve the appearance of the plant and promote reflowering. Like many brassicas, growth and flowering slows in hot weather; the plants will look ragged in the heat of summer but will revive with cooler temperatures and last well into the fall. Light shearing, watering and light fertilization at this time will aid in their recovery. Older clumps may “split” as flowering only occurs on the outer edges and not in the center.

Cultivars of Sweet Alyssum

There are numerous cultivars of sweet alyssum, both from seed and from vegetative propagation. Cultivars include:

‘Aphrodite’ series is compact and features unique colors (apricot, salmon, lemon, and red in addition to white and purple) on early-blooming plants.
CLEAR CRYSTAL® series has extra large, fragrant flowers. It is available in ‘Lavender Shades’, ‘Purple Shades’, and ‘White.’ Grows 6 inches tall and 12 inches wide.
‘Easter Bonnet’ is an early blooming series available in Deep Pink, Deep Rose, and Violet. Grows 4 to 10 inches tall and 10 to 12 inches wide.
‘New Carpet of Snow’ is a compact white-flowering form that grows 3 to 4 inches tall and 8 to 10 inches wide.
‘Oriental Night’ has a compact habit, growing 4 inches tall, with deep violet purple flowers.
‘Pastel Carpet Mix’ is a seed propagated strain that features flowers in a blend of pink, rose, lavender, and cream shades.
‘Rosie O’Day’ is a 1961 All-America Selections winner with rose colored flowers. Plants are compact, reaching 4 inches tall.
‘Royal Carpet’ is a 1953 All-America Selections winner with a compact habit and violet flowers that fade to lavender, creating a bicolor look. Plants grow about 3 inches tall and 10 inches wide.
‘Snow Crystals’ is a vigorous, seed-propagated, tetraploid variety with a mounding habit and large, white flowers. It was the first tetraploid variety available and has improved heat tolerance.
SNOW PRINCESS® (variety ‘Inlbusnopr’ USPP 21,594) is a sterile vegetative hybrid selection from Proven Winners that is has improved heat tolerance.