Hoary alyssum is a biennial that can be a short-lived perennial or annual wildflower in the mustard family (Brassicaceae). It is native to Europe and Asia and has spread to other countries in contaminated crop seeds. It is now found in all states except the southernmost. It is an aggressive invader in fields, rangeland, pastures and other disturbed sites and is listed as a noxious weed in several states. Hoary alyssum grows in full sun, tolerates alkaline and infertile soils and prefers well-drained sandy or rocky soils. It will grow 1 to 3 feet tall and can produce seeds throughout the summer. It has delicate white blooms that appear in clusters in mid-spring through early fall. The leaves have a gray-green color due to the dense star-shaped hairs present. Young plants have a basal rosette of leaves that often die down when flowering occurs, leaving stem leaves. Stems are also densely hairy. Control is by hand pulling or tilling until the seed bank has been depleted. There is no successful chemical control. It is a problem for horses in a field. Insects, Diseases, and Other Plant Problems : No significant problems. Root rot can occur in poorly drained soils.
Curated pairwise relationships between this plant and others in the library — who feeds
whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.
No curated interactions recorded for this species yet.
Also noted by NC State
Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell
apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.
Similar, less problematicLobularia Snow Princess® 'Inlbusnopr'Nemesia strumosa
Full plant profile
Growing Conditions
Plant type
Annual; Perennial; Wildflower
Life cycle
Annual; Biennial; Perennial
Light
Full sun (6 or more hours of direct sunlight a day)
Soil texture
Loam (Silt); Sand; Shallow Rocky
Soil pH
Alkaline (>8.0); Neutral (6.0-8.0)
Soil drainage
Good Drainage | Occasionally Dry
Growth rate
Rapid
Maintenance
High
Canopy layer
4 - Herbaceous
Form & Appearance
Leaf color
Gray/Silver; Green
Leaf type
Simple
Leaf arrangement
Alternate; Rosulate
Leaf shape
Linear; Oblanceolate
Leaf margin
Entire
Leaf feel
Velvety
Leaf size
1-3 inches long, < 1 inch wide
Hairs present
Yes
Leaf detail
1½ to 3 inches long, up to ½ inch wide, toothless, alternate leaves have a pointed or blunt tip and are stalkless. The dense star-shaped hairs give them a grayish-green color. Young plants have a basal rosette of leaves that typically wither away by flowering time. Basal leaves are hairy, oblanceolate and up to 3 inches long with smooth to slightly wavy margins and long stalks
Flower color
White
Flower form
Raceme
Flower shape
Star
Flower size
< 1 inch
Flower detail
Long racemes of small 4 petaled flowers with 6 yellow-green stamens. The petals are deeply lobed giving the impression of 8 petals. Clusters are 1-2 inches across. Blooms until frost.
Bloom time
Fall; Spring; Summer
Fruit color
Green
Fruit type
Capsule
Fruit size
< 1 inch long
Fruit detail
The fruit is a round, flat pod ¼ inch long with the style persistent at the tip and contains many seeds. They are spaced along the length of the elongated branching stems.
Stem color
Green
Stem detail
Single or multi-stem densley hairy.
Wildlife & Ecology
Native status
Non-native
Origin
Europe, China
Food & Medicine
Fruit type
Capsule
Landscape Use
Garden tags
#problem for horses #non-toxic for dogs #non-toxic for cats #seeds #white flowers #annual #weedy #short lived