Ornamental · Brassicaceae
Sweet Alyssum
Lobularia maritima
A low carpet of honey-scented bloom that flowers from spring to fall and pulls in the good bugs.
Full sun
42–56 days
USDA 5–9
3–10 in · 8–25 cm
Overview
Sweet alyssum is the plant you tuck along a path edge or spill over a wall, where its low mounds disappear under tiny honey-scented flowers. It's a member of the cabbage family, easy to grow, and it carries white, pink, or purple bloom from spring right through fall. Few annuals ask for so little and give back so much.
Grow it as a cool-season annual. It loves the mild stretches of spring and fall and tends to sulk in the worst of summer heat, slowing its bloom until cooler weather brings it back. Most plants stay under 10 inches tall and a foot wide, so they knit into a tidy carpet rather than reaching for height.
There's a reason farmers plant it on purpose. The flowers feed hoverflies and parasitic wasps, whose young hunt aphids, which makes a strip of alyssum a small pest-control crew working the garden for free.
Care
The short version: full sun, average soil with sharp drainage, and a light hand with both water and feed. Shear it back when summer heat stalls the bloom and it returns in fall.
Light
Sweet alyssum wants full sun for the heaviest bloom, though it takes a little afternoon shade where summers run hot. The more sun it gets in spring and fall, the thicker the flowers.
Water
Water it regularly while it settles in, then ease off, because it turns drought tolerant once established. What it cannot stand is wet feet, so let the soil dry between drinks and never leave it sitting in standing water.
Soil
Average, well-drained soil suits it fine, and it even shrugs off poor ground. The one thing it insists on is sharp drainage, since soggy soil is what rots the crown.
Humidity
Ordinary outdoor air is all it needs, so there's no number to chase. Good airflow matters more than humidity here, since crowded, damp plants invite downy mildew.
Feeding
Feed lightly through the growing season, roughly once a month. Go heavy and you trade flowers for foliage, so a light hand keeps the bloom coming.
Pruning
Deadhead the spent flowers to keep new ones forming, and clip out any damaged or diseased growth. A harder shear when summer heat stalls the plant resets it for a fresh fall flush.
Size & spacing
Plants stay low, running 3 to 10 inches (8 to 25 cm) tall and 6 to 12 inches (15 to 30 cm) wide. Set them close enough to knit into a carpet but with room for air to move between them.
When to plant
Sweet alyssum runs on the cool ends of the year. Start seeds indoors 6 to 8 weeks before the last frost, or sow straight in the ground a few weeks before that date, and the plants bloom from spring through fall with a lull in the summer heat. In mild climates you can also sow in fall.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 6 to 8 weeks before the last spring frost
- Plant: A few weeks before to around the last spring frost; can also sow in fall in mild climates
- Harvest: Spring through fall, flushing in spring and fall and slowing in peak summer heat
Hardiness
USDA hardiness zones: 5–9
Temperature: down to -29°C
Troubleshooting
Most trouble with sweet alyssum traces back to either heat or too much water. Read the early signs below and you can step in before a slow patch turns into a lost plant. Match what you see, then act.
Wilting plants with rot at the stem and crown
Soggy ground is the cause here. Stem and crown rot sets in when soil stays wet or water pools around the base, and the plant wilts even though the roots are drowning. Pull the affected plants, fix the drainage, and ease off the watering.
Fix:
- Improve soil drainage
- Avoid overwatering and standing water
- Remove affected plants
Yellow leaves with fuzzy growth underneath
Fuzzy growth on the undersides of the leaves, with yellowing showing through on top, points to downy mildew. It takes hold in cool, wet spells when the foliage stays damp. Open the plants up for better airflow, water at the base instead of overhead, and clear away any infected debris.
Fix:
- Improve air circulation
- Avoid overhead watering
- Remove and discard infected plant debris
Bloom stops and the plants turn ragged in midsummer
This is plain heat stress, not death. Sweet alyssum is a cool-season annual, so its growth and flowering slow once summer turns hot. Shear the plants back by about half, water and feed lightly, and they flush again as fall cools.
Fix:
- Shear plants back by about one-half
- Water and lightly fertilize to encourage a new flush
- Allow plants to rebound in cooler fall weather
Toxicity
Good news for households with animals: sweet alyssum is non-toxic. Cats, dogs, and the rest can be around it, nibble it, even sit in it without coming to harm. The honey-scented flowers are safe for curious children to handle too.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe around cats. A curious nibble of the foliage or flowers won't cause poisoning.
Dogs None
No worries for dogs. The plant is listed as non-toxic, so a stray mouthful is nothing to fear.
Horses Safe
Horses can graze near it without harm, as the plant carries no toxins that affect them.
Rabbits Safe
Rabbits can sample the leaves and flowers safely, though any new green is best offered in small amounts.
Livestock Safe
Cattle, goats, and sheep face no danger from it, with nothing in the plant that troubles grazing animals.
Birds Safe
Birds are fine around the plant, and the flowers draw bees and butterflies that birds may hunt in turn.
People Safe
Harmless to people. The honey-scented flowers are pretty and pose no risk to children who handle them.
Varieties
Sweet alyssum comes in a handful of named selections worth knowing, sorted mostly by color and how well they hold up to heat.
Carpet of Snow
A compact, low-spreading selection covered in white flowers, staying around 3 to 4 inches tall.
Royal Carpet
A 1953 All-America Selections winner with violet-purple flowers, holding to about 3 inches tall.
Snow Princess
A vigorous sterile hybrid with white flowers that keeps blooming through heat far better than the old types.
Snow Crystals
A tetraploid bearing larger white flowers along with improved heat tolerance.
Easter Bonnet
An early-blooming series sold as a mix of colors.
Companions
Sweet alyssum earns its place beside vegetables by drawing in the insects that hunt aphids, which is why it's grown in flower strips next to crops like lettuce.
Plant near
Lettuce: Planted as insectary flower strips, sweet alyssum attracts hoverflies (syrphid flies) and parasitic wasps whose larvae prey on aphids, providing biological aphid control in lettuce and other vegetable crops
How to propagate
Sweet alyssum spreads itself with little help, whether you start it from a seed packet or take cuttings of a favorite hybrid.
SeedEasy
Direct sow several weeks before the last spring frost, or start indoors 6 to 8 weeks before transplanting; can also sow in fall in mild climates · Blooms about 6 to 8 weeks from seed
Seed is the easy way in. Sow it on the surface and barely cover it, since the seeds need light to sprout, either directly outside a few weeks before the last frost or indoors 6 to 8 weeks ahead of planting out. Flowers follow in about 6 to 8 weeks, and the plant self-sows freely once it settles in.
Stem cuttingsModerate
During active growth · A few weeks to root
Cuttings are how the sterile hybrids carry on, since cultivars like Snow Princess set little or no seed. Take them during active growth and they root in a few weeks into plants identical to the parent.
Myths
Sweet alyssum has died once it stops blooming and browns in summer.
It is a cool-season annual that usually just slows in the heat. Shear it back, keep it watered, and the cooler days of fall bring it right back into bloom. A ragged midsummer plant is resting, not dead.
Sweet alyssum needs heavy feeding to flower well.
Pile on the fertilizer and you grow a leafy plant with few flowers. A light feed gives you far better bloom, since this plant flowers best when it isn't pushed.