Herb-Robert

Geranium robertianum

Family: Geraniaceae

Other Common Names: Robert geranium, stinky Bob
Weed class: B
Year Listed: 1998
Native to: Europe, Asia and Northern Africa
Is this Weed Toxic?:

not known to be

Why Is It a Noxious Weed?

It poses a threat to the forest understory and to plant diversity in the forests of Western Washington. It is capable of growing under a full, closed canopy. Where it occurs, there appears to be fewer native herbaceous species.

How would I identify it?

General Description

Herb Robert is both a winter and a spring annual or bienennial. It is a low growing plant that is hairy and shallowly rooted. Plants have a pungent odor when crushed.

Flower Description

Flowers have 5 pink petals.

Leaf description

The leaves are deeply dissected and light green. The foliage turns red in late fall.

Stem description

The stems are upright to spreading, hairy and turn red in high light conditions.

Fruit Seed Description

The fruit is a capsule. Seeds are brown and about 2 mm in length.

Where does it grow?

Herb Robert is highly adaptable. It is found in moist forests with canopy closure and on dry rocky outcrops. It is also becoming a significant garden pest in some areas. It is found from sea level to mid-mountainous areas in both the Cascades and Olympics. Please click here to see a county level distribution map of herb-Robert in Washington.

How Does it Reproduce?

Herb Robert reproduces by seeds. The seeds are ejected in response to drying of the capsule. Reports indicate that they may be ejected as far as 15 to 20 feet from the mother plant.

How Do I Control It?

General Control Strategy

Herb Robert is easy to hand-pull. Herbicide is also generally effective.

Mechanical Control

Herb Robert has a very shallow, weak root system which makes hand pulling easy. Aim to pull plants before they go to seed as seeds can survive in the soil for a number of years. Frequently monitor sites and control as needed. Plants can be mowed or cut back with a string trimmer or weed whacker early in the season before they flower.