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Entire healthy mature sweet alyssum plant in a real garden bed, showing growth habit and scale.Primary identification image. 10–20 cm tall, 20–30 cm wide at maturity.

Sweet alyssum

Lobularia maritima (L.) Desv.

Also called: Alyssum

Family
Brassicaceae
Season
Cool-season annual (short-lived perennial in mild climates)
Best grown in
Portland, Oregon

A low, honey-scented flower and the best-documented insectary plant for hoverflies; it is also a brassica.

Safety: Not grown for eating.

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Life cycle & growth stages

  1. 1. SeedSurface-sow; needs light.
  2. 2. SeedlingEmerges in 5–10 days.
  3. 3. FloweringWhite or purple flowers from 6 weeks.
  4. 4. ShearCut back by a third in midsummer.
  5. 5. RebloomFlowers again until frost.

Growth stages are ordered chronologically; timing varies with cultivar, temperature, light and care.

Planting calendar for Portland, Oregon

Start indoors 4–6 weeks before last frost; transplant 1 weeks before to 2 weeks after last frost; direct sow 1 weeks before to 3 weeks after last frost; 45–60 days to maturity from sowing. Windows are derived from the region's average frost dates (last Apr 5, first Nov 5) and are estimates until you confirm your own dates in the calendar.

Sweet alyssumLobularia maritima
PlantStart indoorsDirect sowAutumn sowTransplantTendHarvest
Sweet alyssumFeb 22–Mar 8 (estimate)Mar 29–Apr 26 (estimate)—Mar 29–Apr 19 (estimate)Apr 26–May 13 (estimate)May 13–Oct 15 (estimate)
  • Start seeds indoors: Feb 22 – Mar 8
  • Transplant outdoors: Mar 29 – Apr 19
  • Direct sow: Mar 29 – Apr 26
  • Tend and monitor: Apr 26 – May 13
  • Harvest: May 13 – Oct 15

Spacing & support

In-row 15–20 cm; rows 20–30 cm. Planner footprint: 1 cell of 30 cm, 2 plants per cell.

Side-profile diagram of mature sweet alyssum: canopy 10–20 cm tall, 20–30 cm wide, shallow root zone, support and harvest-access envelope.

Soil & water

Soil
Any well-drained soil
pH
6–7.5
Fertility
low
Water
Moderate; shear and water to rebloom.
Frost
half hardy; tolerates frost

Support & training

No support structure needed.

Sweet alyssum mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Harvest signs

  • Shear by a third when flowering slows

Common problems

Pests: flea beetles

Diseases: clubroot (as a brassica)

Appearance alone is not a diagnosis; confirm with a regional extension guide.

Side-by-side: healthy sweet alyssum leaf or fruit and an example of clubroot.

Container growing

  • Minimum 2 L (10 cm deep)
  • Use quality potting mix and water more frequently
Mature sweet alyssum in a correctly sized container (2 L or more) with drainage visible.

Companion overview

4 reviewed relationship records (evidence: medium).

Supported or conditional

Broccoli, Kale, Lettuce, Strawberry

Avoid or separate

None with evidence

Full companion profile

Crop rotation

Avoid planting sweet alyssum or other cabbage family crops in the same spot for 3 years. Rotation is about previous seasons, not about live neighbours.

Year 1Year 2Year 3BrassicaceaeOther familyOther familyback after 3+ years

Shared risks in Brassicaceae: clubroot, cabbage root fly, cabbage white caterpillars.

Crop rotation hub

Sources, reviewer & update

Sources

Reviewer: Garden Planner editorial team (pending independent horticultural review)

Last reviewed: August 15, 2026 · version 1

Found an error or have feedback? Let us know.

Growing sweet alyssum

Sweet alyssum is sown indoors or directly around the last frost and flowers within 6–8 weeks, continuing for months if sheared back once in midsummer. It is only 10–20 cm tall, so it fits at bed edges and between crops without shading them.

Sweet alyssum seed beside a ruler or coin for scale.
Sweet alyssum seedling at cotyledon and first-true-leaf stage, in soil, distinguishable from common weeds.
Sweet alyssum at transplant-ready stage with root ball visible beside the cell or pot.

Its small, open flowers are among the most attractive to hoverflies (syrphids), whose larvae eat aphids. Field agronomy in organic broccoli and lettuce (Brennan 2016) showed that alyssum strips support this biocontrol, with the practical lesson that a small share of the bed in alyssum, within a few metres of the crop, is enough; more alyssum means more competition.

Two or more mature sweet alyssum plants with a tape measure showing in-row spacing (15–20 cm).
Sweet alyssum flower detail or bolting stage.

Alyssum is a brassica: it can host flea beetles and clubroot, and counts as a brassica for rotation.

Edible parts and safety

Not grown for eating. Not grown for eating.

Sweet alyssum at end of season: seed head, dry pod, spent plant or removal stage.

Pests and diseases

Common pests: flea beetles. Common diseases: clubroot (as a brassica). These vary by region; a photograph is an example, not a diagnosis. See the pest and disease guides and your local extension service.

flea beetles on sweet alyssum, with a wider damage-context view.

Timeline

Season timeline for sweet alyssum: sowing, transplanting, flowering, harvest and bed occupancy aligned to frost dates.Text alternative: Start seeds indoors Feb 22–Mar 8; Transplant outdoors Mar 29–Apr 19; Direct sow Mar 29–Apr 26; Tend and monitor Apr 26–May 13; Harvest May 13–Oct 15.

Related plants

See also: Brassicaceae family page · crop rotation · regional calendar · guides

Our Methodology & Sources

We synthesize peer-reviewed research, university extension publications, and trusted horticulture resources. Our evidence levels help you understand how strong the science is behind the guidance.

Evidence tiers

Supported evidenceConsistent results from multiple robust studies
Traditional claimHistorical use reported, limited scientific support
Context dependentMixed or variable results across conditions
No verified relationshipNo reliable evidence identified

Primary source types

  • Peer-reviewed journal articles
  • University extension publications
  • Government & research institute reports
  • Systematic reviews & meta-analyses

Last updated

August 24, 2026

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