Sweet Alyssum

ANNUALS > ALYSSUM

Imagine billowing, scented white ‘ornamental clouds’ covering a tract of your garden.

Or frothy, colourful purple clusters tumbling out of a planter atop your wall.

Add in butterflies and bees, and revel in – besides the soothing colours – the fragrance.

That’s what you’ll get with Sweet Alyssum, a charmer that is easy to grow and is even relatively fuss-free.

Overview

Botanical Name	Lobularia maritima
Common Name(s)	Sweet Alyssum
Plant Type	Annual / Perennial
Native Area	Europe, Asia, North Africa
Hardiness Rating	H3
Foliage	Deciduous
Flowers	Small and often white, purple or pink – very fragrant
Plant Out	May, June
Flowering Months	June, July, August, September

Sweet Alyssum are very easy-grow annuals that are not at all fussy about soil.

They have heights from 10-25cm and spreads from 20-45cm.

The leaves are long and narrow, oval-to-oblong shaped and usually slightly hairy. They are greyish-green or silvery-green in colour. 

One can best describe these plants as mounding, trailing, billowing clouds of zillions of very fragrant and ultra-cute tiny flowers borne in lush clusters and clumps.

As there is such a thing as an ornamental flower, we may call Sweet Alyssum an ‘ornamental cloud’.

Colours are limited to white, and several tones of pink and purple.

Very new cultivars that bear flowers in oranges and reds are just showing up in the United States.

No matter what the colour, these wee flowers pull pollinators in droves.

However, Sweet Alyssum cultivars, unlike quite a number of other flowers’ cultivars, do not differ only in colour of the flower and some or another attribute such as a few inches in height or variegation.

The considerable variance among these cultivars extends to height, spread, variegation vigour, fragrance, blooming season, size of blooms, besides – of course – the colour of the flowers.

Though all varieties of Sweet Alyssum (and also Alyssum) are recognised as being excellent companion plants for roses, geraniums, snapdragons, and other flowering plants, we reckon that with all their genuinely pleasing and heart-lightening characteristics, they will make just as excellent garden, porch or patio companions for you! 

Alyssum Vs Sweet Alyssum

Gardeners know that in the universe of plants and gardening we have our fair share of twins – and also imposters!

This article is about one such plant, Sweet Alyssum, which is twins with ‘plain’ Alyssum – these two plants are often mistaken for each other.

We leave it up to the reader to decide which is the real deal and which is the imposter.

Alyssum are plants belonging to the Alyssum genus whereas Sweet Alyssum are plants of the Lobularia genus and are sometimes – incorrectly and confusingly – referred to as just ‘Alyssum’.

In the United States they are also known as ’Sweet Alison’. 

Not only do these two different genera’s respective species bear a close resemblance, they were originally classified in one and the same genus namely Alyssum.

Lobularia was separated out from it over two centuries ago but we’re still stuck with the confusion.

Both genera belong to the Mustard or Brassica family.

Though Genus Lobularia includes only five species, one of these, L. maritima, is parent to dozens of cultivars, several of which have been awarded the RHS Award of Garden Merit.

These plants have not only become garden favourites but are even also automatic choices for several different garden purposes.

These are popularly known as Sweet Alyssum.

Habitat & Growing Conditions

When one sees this charming, floriferous and somewhat dainty plant, one would feel stretched to believe that parent species Lobularia maritima’s habitats are gravelly and sandy locales, including even sand dunes, in their native regions of the Mediterranean.

It is often found close to coastal areas including near the beach and on cliffs.

With a hardiness rating of H3, Lobularia varieties are that anomaly, half-hardy annuals.

They are effectively annuals in many parts of the United Kingdom but if you live somewhere along the southern coast or a very mild region where they can survive the winter outdoors, you’ll have short-lived perennials.

How To Grow Sweet Alyssum

To get a head start on Sweet Alyssum in the garden, seeds are generally sown in February or March – either in a heated propagator or on a sunny windowsill.

We cover this seed-growing process in a separate guide.

Planting Out

After the soil temperature has crossed 16°C, young plants started indoors can be transplanted outdoors.

Before doing so, harden them progressively for one week.

However, though you can sow Sweet Alyssum indoors in a seed tray to start them before spring, the truth is that for easy-grow annuals that are meant for planting in a bed, be it for edging, it may well be more trouble than it is worth to sow Sweet Alyssum in a tray and then transplant outdoors if your region’s growing season is not very short.

Now if you would like to have Sweet Alyssum flowering by mid-spring in a planter for the patio parapet or in a hanging basket for the front door, by all means start them early indoors.

You can do so directly in the container itself to avoid transplanting and the possibility of losing some seedlings.

These plants flower in five to seven weeks.

Whether sowing seeds or transplanting, make note of the spread of the variety in question and space accordingly as many are mat-forming and several varieties have a trailing habit.

Where To Plant

Perhaps a better question would be “Where not to Plant Sweet Alyssum”, for this incredibly versatile plant has a vast range of garden uses.

Here are some examples:

• The ‘classic’ usage is for borders and also, specifically, for edging, be it for a bed or along a walkway.
• In mild regions they make excellent groundcover, including on slopes and verges.
• Planted in close proximity these plants produce the effect of a floral cloud or blanket.  
• Mass plantings of any kind will draw bees and butterflies in quantity.
• They make charming companion plants that set off taller flowering plants of richer, deeper, hues.
• They are eminently suitable for both filler and accents in rock gardens.
• They can be hung in a basket by a window or set in a container on the patio’s parapet.
• You can probably think of other and further garden purposes for Sweet Alyssum!

Keep in mind that this ’sweet’ plant descends from a maritime species (as reflected in its scientific name); therefore, many varieties are good to grow in coastal regions and even by the seaside.

Ongoing Plant Care

Sweet Alyssums are sow-and-grow annuals; in truth even a child can grow them – in fact, they’re lovely little plants with which to hook children to gardening.

Soil Requirements

The soil should neither be poor nor overly rich.

Light sand- and chalk-based loam amended with about 20% organic compost will be ideal.

Though this fuss-free plant will readily grow in poor soils, heavy soils must be avoided.

Soil pH should ideally be in the range of slightly acidic to neutral, that is 6.1-7.3, though there is certainly considerable leeway with this easy-going plant.

The soil should drain very well and be kept slightly moist – this really is the only hard-and-fast rule for Sweet Alyssum care.

The soil should not be allowed to dry out completely nor should it get waterlogged.

Aspect

Sweet Alyssum seeds need light to germinate.

Therefore, sow seeds by merely nudging them into the soil or dropping them on the soil and then sprinkling the finest dusting of soil on them.

Site Sweet Alyssums in full sun. Southern or eastern exposure is preferable, and is a must in the colder regions of the United Kingdom.

Be aware that varieties with darker and more saturated floral shades tolerate heat less well than the white and light-coloured ones so in the warmest parts of the country these won’t mind some afternoon shade or filtered sunlight.

That explained, if shade is not available, no problem – if there’s a dainty little charmer that can tolerate heat, it’s Sweet Alyssum.

Watering

These plants need regular watering.

After seedlings have sprouted they should be watered moderately every other day for about four weeks.

After this period the watering frequency can gradually be reduced and the amount of water gradually increased.

Accounting for rainfall, you should water such that the soil does not get dried out nor becomes soggy.

Weeding

Weeds will pose a problem for Sweet Alyssum and in view of the thick mat these plants make, weeding will be an even bigger chore than it is.

Circumvent the problem by applying about 4cm of mulch around the plants when they are young but do so about 6cm from the main stem to leave the young plants sufficient space to grow.

Fertilising

Sweet Alyssum do not need fertilising but it will help.

A bi-monthly feeding with a balanced liquid fertiliser, appropriately diluted, will prove to be a quick and efficient method, and also an effective one.

Pruning

Keep cutting old and spent flower clusters to keep those blooms coming.

Though this is the default (and probably only) gardening task needed for Sweet Alyssum in any kinds of containers, you have a choice for plants in your garden or anywhere in the open.

Sweet Alyssum self-seeds quite well so if you allow spent blooms to go to seed, and if you live in a region where this plant grows as an annual (most parts of the UK), then the following season you’ll get new plants, courtesy of Mother Nature.

Of course, they will not resemble the originals and will likely revert to the original white – again, that’s Mother Nature!

Apart from that, halfway through the season or if the plants look overgrown and unkempt, cut them back by a half.

“I cut back Sweet Alyssums mid-season, as by this point, they are often starting to look a bit straggly and bare in patches,” says Master Horticulturist Colin Skelly.

“Cutting back helps to restore vigour and stimulates fresh growth and re-flowering into late summer and early autumn.”

This will not only stimulate fresh growth, but cooler weather in autumn will also combine to give the plants renewed vigour and bring a second bloom.

Sweet Alyssum Varieties

Underneath we describe a selection of some best-selling varieties identified by cultivar name, omitting Lobularia maritima from the names.

‘Wonderland’, ‘Easter Bonnet’, ‘Clear Crystals’, and ‘Golf’ are the names of the series, each of which has a few member-cultivars.

The blooming period is strongly dependent on several factors, such as sun, watering, fertilising, and cutting back.

However, you can count on all varieties producing flowers for at least a solid three months, for the most part in the summer.

‘Wonderland White’ is renowned for the honey-sweet fragrance of its little blossoms. It is also known for being a vigorous variety. The flowers are a dense, chalky white and they occur in incredible profusion. It reaches a height of 10cm and a spread of 30-40cm. RHS Award of Garden Merit.

‘Snowdrift’ is a very floriferous variety that produces pure white flowers with an intense fragrance. They have distinctive rounded inflorescences. It reaches a height of about 15cm and a spread of about 30cm. RHS Award of Garden Merit.

‘Frosty Knight’ is not very floriferous nor very vigorous either but it is valued for another reason. It has variegated foliage: the leaves have a substantial lemon-yellow edging which adds to the visual appeal. The flowers are bright white and the plant attains heights of 12-15cm. 

‘Violet Queen’ is the basketball player among these diminutive plants as it attains a height of up to 25cm. The flowers have a purplish hue with the tones varying from lilac to rich, saturated purple. They have a light, sweet scent. RHS Award of Garden Merit.

‘New Carpet of Snow’ lives up to its billing because the flowers are truly snowy white. It is an ‘improvement’ on the ‘Snow Carpet’ or ‘Carpet of Snow’ variety. This variety has a long blooming season that typically starts and ends later than those of other varieties. It reaches a height of about 13cm and a spread of 13-20cm. 

‘Rosie O’Day’ is a very popular variety. The flowers are white when they open and turn pink-purple as they mature; thus, this plant essentially bears flowers in white and in different tints of pink-purple. Flower heads are more rounded than most. Reaching a height of 7-10cm it is very much of a mat-forming habit. RHS Award of Garden Merit.

‘Easter Bonnet Violet’ attains a height of up to 15cm and a spread of about 45cm. It bears clusters of mid-purple flowers that have a pleasantly sweet scent. This variety also has one of the longest blooming seasons but it is one of the last to stop blooming in late autumn.

‘Easter Bonnet Lavender’ is among the shortest cultivars at only about 8-10cm. The flowers are of the lightest, gentlest shade of lavender and they have a light and gentle fragrance to match. It is one of the earliest to bloom and has one of the longest blooming seasons. It is known to be one of the least vigorous and least resistant cultivars.

‘Wonderland Deep Purple’ produces masses of flowers that are possibly the most intensely hued among Sweet Alyssum, being of a deep, brilliant, jewel-like purple tone. It grows to only about 10cm but has a spread of 30-45cm. It is a very vigorous variety.

‘Golf Series’ includes varieties in different colours. Its main attraction is the dense profusion with which it produces blooms. The Mix includes flowers in white, baby pink, and light purple. It rises to only about 10cm, making it a proper mat-forming variety. RHS Award of Garden Merit.

‘Clear Crystals’ is renowned for its vigour and its larger flowers, which are scented to boot. Plants reach a good height of up to 23cm and they have a spread of 30-35cm. The Mix includes seeds for flowers in white, pink, lavender, and rich purple. 

Common Problems

Sweet Alyssum can be attacked by slugs and snails, and flea beetles, all of which are fairly easy to control.

They are susceptible to only two or three diseases but, unfortunately, these are serious ones, being downy mildew and white blister.

Slugs & Snails

Slugs and snails can be dealt with using good old beer traps.

If that doesn’t work, you can try Aluminium Sulphate in a 1:60 dilution. Pour it around the crown.

Other remedies, such as microscopic nematodes, against these pests are also available.

Flea Beetles

Flea beetles are best defeated by releasing ladybugs, lacewings, and other beneficial insects.

You can also try approved chemical pesticides.

Downy Mildew & White Blister

In an unfortunate twist, one of the very garden purposes of this plant, which is to create a groundcover or an ornamental floral blanket, is what makes it so susceptible to downy mildew and white blister.

If you intend to grow Sweet Alyssum in such a way you will have to watch out for these diseases because when these plants are hemmed in and, therefore, do not enjoy good air circulation and are subject to high humidity, these two diseases can affect them.

If your plants are affected by either disease you should promptly remove all diseased parts or even entire plants, and destroy them.

Try to open up the (remaining) plants by pruning them, and try to improve air circulation and exposure to sunlight.

Buying Sweet Alyssum

Varieties of Sweet Alyssum are available in pots during spring and early summer at nurseries.

The floriferousness and fragrance and the charming quality of the dainty flowers make them reliable sellers.

Seed packets are perhaps even more widely available and are a popular and easy way to grow these plants.

You can find them at brick-and-mortar garden centres as well as online at seed and plant merchants’ sites.