Ornamental · Brassicaceae
Sweet Alyssum
Lobularia maritima
A fast-spreading carpet of honey-scented bloom that runs from spring to fall and calls in the good bugs.
Full sun
42–56 days
USDA 5–9
3–10 in · 8–25 cm
Overview
Sweet alyssum packs a lot of reward into a tiny plant. Tuck it along a path edge or let it tumble over a wall, and it races to fill in with mounds of tiny honey-scented flowers. It hails from the cabbage family, grows with almost no fuss, and pumps out white, pink, or purple bloom from spring clear through fall.
Grow it as a cool-season annual and it hits full stride in the mild weather of spring and fall. Summer's peak heat makes it coast and slow its bloom for a while, then cooler air fires it back up. Most plants top out under 10 inches tall and a foot wide, so they knit into a dense carpet instead of stretching skyward.
Here's what makes it a real garden workhorse: the flowers pull in hoverflies and parasitic wasps, and their young go hunting aphids. Plant a strip of alyssum and you set loose a whole crew of pest fighters that patrol the beds for free.
Care
The short version: full sun, average soil with sharp drainage, and a light touch on water and feed. When summer heat stalls the bloom, shear it back and watch it charge into fall.
Light
Aim for full sun and sweet alyssum flowers like mad, though a bit of afternoon shade helps where summers scorch. Pile on the spring and fall sun and the blooms come thicker and faster.
Water
Water it regularly to get it rooted, then back way off, because it turns drought tolerant once it's established. Just keep it out of standing water, and let the soil dry between drinks so the roots stay happy.
Soil
Average well-drained soil gets it going, and it powers through poor ground without complaint. The one must-have is sharp drainage, since soggy soil is what rots the crown and stops it cold.
Humidity
Plain outdoor air is all it wants, so skip the humidity readings. Airflow is the real winner here, because crowded, damp plants hand downy mildew an easy opening.
Feeding
Feed it lightly through the growing season, about once a month, and that's the sweet spot. Overdo it and you grow leaves instead of flowers, so a light hand keeps the blooms firing.
Pruning
Deadhead the spent flowers and fresh ones keep pushing out, and clip away anything damaged or diseased to keep it charging. When summer heat stalls the plant, a bold shear resets it for a big fall comeback.
Size & spacing
It stays low and busy at 3 to 10 inches (8 to 25 cm) tall and 6 to 12 inches (15 to 30 cm) wide. Space plants close enough to weave into a carpet, but leave room for air to move so they keep racing along.
When to plant
Sweet alyssum thrives on the cool ends of the year, so time it right and it takes off. Start seeds indoors 6 to 8 weeks before the last frost, or sow straight into the ground a few weeks before that, and it blooms from spring through fall with a short summer breather. In mild climates, sow in fall for even more.
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
Nearly every problem with sweet alyssum traces back to heat or too much water, and both are easy to turn around. Spot the early signs below and jump in before a slow patch drags the whole planting down. Match the symptom, then move.
Wilting plants with rot at the stem and crown
Soggy ground is behind this one. Stem and crown rot moves in when soil stays wet or water pools at the base, and the plant wilts while its roots drown. Yank the affected plants, fix the drainage fast, and dial back the watering.
Fix:
- Improve soil drainage
- Avoid overwatering and standing water
- Remove affected plants
Yellow leaves with fuzzy growth underneath
Catch fuzzy growth on the leaf undersides with yellowing bleeding through on top and you've got downy mildew. It grabs hold in cool, wet spells when the foliage stays damp. Open the plants up for airflow, water at the base instead of overhead, and clear out any infected debris.
Fix:
- Improve air circulation
- Avoid overhead watering
- Remove and discard infected plant debris
Bloom stalls and plants turn ragged in midsummer heat
No need to give up, this is just heat stress. Sweet alyssum is a cool-season annual, so it downshifts its growth and flowering once summer bakes. Shear the plants back by about half, water and feed lightly, and they roar back with a fresh flush as fall cools down.
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
Great news for pet-filled homes: sweet alyssum is non-toxic. Cats, dogs, and everyone else can romp through it, nibble it, even nap in it without harm. Those honey-scented flowers are safe for eager young hands to explore too.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Cats are in the clear, and a curious nibble of the leaves or flowers won't poison them.
Dogs None
Dogs have nothing to fear here, since the plant is non-toxic and a stray mouthful does no harm.
Horses Safe
Horses can graze right alongside it safely, because it holds no toxins that affect them.
Rabbits Safe
Rabbits can munch the leaves and flowers safely, though any new green is best offered in small amounts.
Livestock Safe
Cattle, goats, and sheep are fine around it, since nothing in the plant troubles grazing animals.
Birds Safe
Birds are safe near it, and the flowers pull in bees and butterflies that birds may chase down.
People Safe
People are perfectly safe with it, and the honey-scented flowers are harmless for kids to pick and handle.
Varieties
A lively handful of named selections is worth chasing down, sorted mostly by flower color and by how hard they push through heat.
Carpet of Snow
A compact, low-spreading go-getter that stays around 3 to 4 inches tall under a blanket of white flowers.
Royal Carpet
A 1953 All-America Selections winner in violet-purple that holds to about 3 inches tall.
Snow Princess
A powerhouse sterile white hybrid that keeps flowering through heat long after the old types quit.
Snow Crystals
A tetraploid that throws larger white flowers and pushes through heat better too.
Easter Bonnet
An early-blooming series that comes as a bright 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 multiplies almost on its own, so grab a seed packet or snip a few cuttings from a hybrid you love and let it run.
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 fast, easy launch. Scatter it on the surface and barely cover it, since the seeds need light to sprout, either outdoors a few weeks before the last frost or indoors 6 to 8 weeks before you plant out. Flowers burst open in about 6 to 8 weeks, and once it settles in it self-sows all over on its own.
Stem cuttingsModerate
During active growth · A few weeks to root
Cuttings keep the sterile hybrids rolling, since cultivars like Snow Princess barely set seed. Take them while the plant is growing hard and they root in a few weeks into fresh copies of the parent.
Myths
Sweet alyssum is finished once it browns and quits blooming in summer.
Not a chance, it's a cool-season annual just coasting through the heat. Shear it back, keep it watered, and cooler fall days launch it right back into bloom. A ragged midsummer plant is resting, not dead.
Sweet alyssum needs heavy feeding to flower well.
Dump on the fertilizer and you grow a leafy plant with barely any flowers. A light feed gets you way more bloom, because this plant flowers hardest when you don't push it.