Lobularia - Sweet Alyssum: Sowing, Planting and Growing

Botany and description

Lobularia maritima (syn. Alyssum maritimum), commonly known as Sweet alyssum or Seaside alyssum, is an annual plant belonging to the Brassicaceae family (formerly called Cruciferae). The Lobularia genus comprises 5 species, some perennial, others annual: Lobularia maritima is the most widely cultivated in our gardens. The species typically bears white flowers and grey foliage, earning it the nickname “Basket of Silver”. There are numerous horticultural varieties, sometimes more compact or with different flower colours (pink, purple, crimson…).

Alyssum maritimum, botanical plate from 1896

Lobularia maritima is native to the Mediterranean basin. However, this plant has become naturalised in other parts of the world: along the Bay of Biscay coastline, and even in California. It thrives growing among rocks, in sandy soil, but is occasionally found on slopes or wasteland in limestone areas. Although cultivated as an annual, it’s not uncommon to find self-sown plants in the most unexpected garden spots: rockeries, borders, paving cracks, walls and even containers, thus perpetuating the plant.

Sweet alyssum forms small, densely branched clumps reaching 30 cm in height. The base of the clumps is slightly woody. The foliage is alternate and sessile, with a glaucous colour and greyish underside. The leaves are typically villous, single and narrow.

Flowering is exceptionally long-lasting, extending from March to October in mild climates, starting from June further north. The inflorescence begins as a rounded raceme (a type of flower cluster) that elongates over time. Each flower, 3-4 mm in diameter, displays 4 sepals, 4 rounded petals (typical of the family!) and 6 stamens with yellow anthers. The blooms are notably fragrant, with a scent reminiscent of honey sweets. Pollination is entomophilous, carried out by insects, which are strongly attracted to sweet alyssum flowers.

White and mauve sweet alyssum. Right: close-up of flower

The infructescence is elongated and bears numerous villous siliculas (small siliquas, typical of Brassicaceae fruits). Each silicula contains two seeds. Seed dispersal is anemochoric, with seeds carried by wind.

The larvae of the Southern Small White butterfly (Pieris mannii) feed on sweet alyssum foliage. In fact, lobularias are used in American cabbage fields to attract these caterpillars away from crops – an organic, natural pest control method.

As the plant grows quickly and provides rapid ground cover, agricultural research is exploring lobularia’s potential as a cover crop. Its blooms attract numerous pollinating insects too. Consider this for your own vegetable garden!

Our most beautiful varieties

Sweet alyssum or Lobularia maritima is the most widely cultivated species of the genus in our region. It has been declinated into numerous varieties: with pink, mauve or violet flowering; or sometimes more compact. Here are our favourites:

Lobularia Snow Princess

Sweet Alyssum 'Snow Princess', also called Lobularia, is a vigorous annual plant with a creeping habit. From the start of the season, it forms a tapetum of small white fragrant flowers, 2 to 8 cm in diameter, gathered in clusters.

• Flowering time August to November
• Height at maturity 40 cm

See the product sheet

Lobularia maritima Princess in Purple - Sweet Alyssum

Sweet Alyssum 'Princess in Purple' is a vigorous annual plant with a creeping habit. Very floriferous, it produces from the start of the season a tapetum of small fragrant flowers, 2 to 8 cm in diameter, gathered in clusters of lavender to purple-violet flowers.

• Flowering time August to November
• Height at maturity 40 cm

See the product sheet

Lobularia maritima Snow Crystals

Sweet Alyssum 'Snow Crystals' forms very uniform snowy tapetums, as its immaculate flowers are particularly large and perfectly cover its compact foliage. It quickly forms dense, carpeting cushions that work wonders in borders, as well as in hanging baskets and flowering containers.

• Flowering time June to September
• Height at maturity 15 cm

See the product sheet

Sweet Alyssum Rosie ODay

Lobularia maritima procumbens or Sweet Alyssum 'Rosie O'Day' is a very pretty variety of fragrant sweet alyssum with pink, scented flowering. This small annual plant with a creeping habit forms dense, fragrant cushions in one year that work wonders in rockeries and flowering containers.

• Flowering time July to October
• Height at maturity 12 cm

See the product sheet

Lobularia maritima Royal Carpet

This Lobularia maritima or Sweet Alyssum 'Royal Carpet' is an annual groundcover plant with very attractive flowering. Indeed, its numerous small violet-purple flowers appear from June onwards, renewing themselves until October. They are abundant, fragrant and attract many insects.

• Flowering time July to November
• Height at maturity 15 cm

See the product sheet

If you can’t decide on the colour of your sweet alyssums, mixed varieties also exist.

Sweet Alyssum Magic Circles Mix

This mix of Lobularia maritima or Dwarf Alyssum 'Magic Circles' is a collection of annual groundcover plants with very attractive flowering. Indeed, the numerous small flowers in varied colours appear from June onwards, renewing themselves until October.

• Flowering time July to November
• Height at maturity 15 cm

See the product sheet

Planting alyssums

Where to plant?

Lobularias enjoy the sun and tolerate partial shade. The soil should be light and well-draining, preferably alkaline to neutral. It will thrive in ordinary, stony or sandy soil, even very dry. Excessive moisture causes it to wither. Sweet alyssum is capable of growing in very little soil.

Like basket-of-gold (Alyssum sp.), sweet alyssum makes an excellent ground cover for slightly dry areas (such as a sunny slope) where other plants struggle to establish. It can be used to brighten up a rockery or certain sun-baked flower beds, along the edge of a sunny border. Sweet alyssum can also be inserted at the top of a dry stone wall or nestled between paving stones or in the crevices of walls.

Note that lobularias also thrive in pots, planters or hanging baskets on sunny balconies and terraces.

Lobularia or sweet alyssum

When to plant?

Lobularia plug plants can be planted in spring (ideally from March to May), until early summer, in the ground or in containers. Sowing is done in spring, but can be attempted in autumn in mild climates.

How to plant?

In the ground

• By sowing, prepare the soil carefully: weed, loosen well and lighten with a bit of compost if needed. Rake the soil smooth and sow thinly by scattering. Cover with a little compost and water with a fine spray. Continue watering, without excess, for at least two months after sowing. Thin out the young plants if necessary if sown too thickly;
• By planting small buckets or plug plants: dig a hole twice the size of the root ball. Loosen the soil well and add some compost, or even a few gravel stones, if it is too heavy. Plant your sweet alyssum and backfill the hole with the excavated soil, but without burying the collar. Gently firm the soil around the base with your hands. Water thoroughly to avoid any “air pockets” between the soil and the roots.

Allow for 5 to 7 sweet alyssum plants per square metre!

In pots

• Spread a good layer of drainage (gravel or clay pebbles) at the bottom of the container, which must have one or more drainage holes;
• Plant the bucket in a mix of ordinary soil, compost for Mediterranean plants and coarse sand;
• Water to encourage establishment, then once every two weeks;
• Place your containers in full sun.

Sweet alyssum planted in a pot

Maintenance, Pruning and Care for Lobularia

Watering

Lobularias are very drought-tolerant. You can therefore forget about watering once flowering begins in spring and when the plant covers the ground well.

In pots, allow the surface of the compost to dry out between waterings.

Pruning

Don’t hesitate to give a light trim with garden shears to the clusters of faded flowers. This will encourage the plant to produce more flowers and thus prolong the flowering period.

You can also pinch back young shoots in spring to help the young plant become more ramified.

Fertiliser

For pot-grown plants only, alyssums can be given a liquid fertiliser for flowering plants every 3 to 4 weeks.

For plants in the ground, do not enrich your soil for alyssums. Indeed, the plant may produce foliage at the expense of flowering.

Possible diseases and pests

Young Lobularia plants attract slugs and snails early in the season. Keep an eye on your sweet alyssum when planted in the ground.

The plant also hosts insects such as cabbage white caterpillars, aphids, thrips… though these rarely cause significant harm. In cases of severe aphid infestation, you can spray water mixed with black soap.

In hot and humid weather, alyssums may occasionally suffer from powdery mildew (white spots or coating) or downy mildew (rust-coloured pustules). However, this is rare and mostly occurs in poorly drained soil. Prune affected parts and avoid watering the foliage. To prevent and treat powdery mildew, follow our advice: “Powdery mildew or white mould: prevention and treatment”.

How to propagate sweet alyssum?

The simplest method remains sowing. In fact, the plant often takes care of reseeding itself in the most unexpected spots in the garden: between paving stones or rocks, for example.

By direct sowing in spring

• Prepare the soil carefully: weed, loosen well and lighten with a bit of compost if needed;
• Rake the soil to a fine tilth and sow thinly by scattering;
• Cover with a little compost and water with a fine spray;
• Continue watering, without overdoing it, for at least two months after sowing;
• Thin out the young plants if necessary, spacing them 20cm apart, if sown too thickly.

By sowing in a seed tray, under a cold frame (protected from frost) at winter’s end:

• Sow thinly in well-sieved seed compost;
• Cover with a little compost and water with a fine spray;
• Continue watering, without overdoing it;
• After two months, you can transplant them into pots or directly into the ground.

A few ideas for plant combinations

The Sweet Alyssum is unrivalled for greening up a neglected corner of the garden, whether it’s deemed too dry or the soil too poor.

In a dry or gravel garden, Sweet Alyssum adds a lively touch with its flowers ranging from white to mauve or violet. Lobularia works wonders on slopes, in dry rockeries, sun-baked borders and even in patio containers.

Sweet Alyssum pairs easily with other rockery perennial plants: for example alyssums or Basket-of-gold, but also aubrietas, ageratums or rock bellflowers.

It thrives alongside Mediterranean perennial plants, all as undemanding as itself: lavender cottons, artemisias, catmints, globe thistles, sea hollies, lamb’s ears, rock roses… not forgetting southern bushes like lavenders, rosemary, bushy sages…

In a rockery, a beautiful combination of Sweet Alyssum, ageratum, artemisia and aubrieta