Key Facts
- A member of the mustard family with small white four petaled flowers
- Often grown or encountered as a weedy annual or biennial that self seeds
- Common in disturbed, dry, or rocky sites and along roadsides
- Spreads primarily by prolific seed production
- Tolerates poor and alkaline soils and dry conditions
- Flowers typically appear in late spring into summer in temperate climates
- Management focuses on removing plants before they set seed
Hoary Alyssum is a Eurasian mustard family plant with small white four petaled flowers that commonly appears in disturbed ground. It establishes readily from seed and can be useful as a quick colonizer of poor, dry sites while also spreading aggressively if allowed to set seed.
Identification
A low to medium height erect annual or biennial reaching about 12 to 36 inches tall with clusters of small white four petaled flowers. Plants form loose clumps roughly 12 to 24 inches across and are most noticeable when in bloom from late spring into summer in temperate regions.
Where it grows and best uses
Hoary Alyssum tolerates poor, dry and often alkaline soils so it appears commonly on roadsides, rocky or disturbed sites and other open sunny places. That tolerance makes it a candidate for temporary cover on very poor soil but it is usually treated as a weed because it self seeds and forms persistent patches.
Planting and spacing
Propagation is primarily by seed. If intentionally seeded, give plants at least a foot of spacing to match the typical clump size and to reduce competition. Because plants reproduce prolifically, avoid planting near desirable perennials or native wildflower areas where it can naturalize.
Water and soil
Plants prefer well drained soils and tolerate dry to average moisture levels. They perform on poor rocky or alkaline substrates and usually show reduced vigor in poorly drained sites. Extra irrigation is not needed and may encourage larger, more vigorous plants that produce more seed.
Bloom season and after flowering care
Flowers typically appear in late spring and continue into summer in temperate climates. Management and after flowering care focus on preventing seed production. Remove or cut plants before seed pods mature to reduce local spread. Repeated removal of seedlings in subsequent seasons helps deplete the seed bank.
Controlling spread
Spread is almost entirely by prolific seed production. Prevent flowering and destroy plants before seed set for the best control. Hand pulling of young plants is effective in small patches. For larger infestations, repeated mowing or cutting before seed development reduces seed return to the soil. Consult regional invasive plant resources for herbicide guidance suitable to your area.
Frequently asked questions
- How fast does Hoary Alyssum grow?
- It often establishes quickly from seed and can reach typical adult height within a single season as an annual. Rapid self seeding lets local stands form over one or more seasons.
- Is Hoary Alyssum invasive?
- It is a non native species that commonly naturalizes in disturbed temperate habitats and is often treated as a weed because it forms persistent patches by self seeding.
- When should I remove plants to stop spread?
- Remove or cut plants before seed pods mature, generally before late summer in temperate regions. Repeated removal of seedlings the following seasons reduces recolonization.
- What soil and light does it prefer?
- It establishes best in full sun to partial shade on well drained poor to average soils and tolerates dry and rocky or alkaline conditions.
- Is it safe around pets and livestock?
- Records on toxicity are inconsistent across sources. Avoid feeding to livestock and check local extension or poison control for region specific guidance.
Related Plants
