Geranium Robertianum, also called Herb Robert or Stinky Bob, is a wild geranium plant species (cranesbills) and member of the geraniaceae family.
It is an abundant species and is native to Europe, Asia, and North Africa.
In these regions, it can grow to altitudes up to 1500 m.
It was introduced into other temperate climate zones (especially in North America) as an ornamental garden plant.
In the US State Washington it is now considered a noxious weed because it heavily out competes native plants and plant diversity is on the decline, especially in the forests. They are able to grow under fully, closed forest canopy with very low light levels and overgrow many other understory plants.
The have the ability to actively move their leafs towards the sunlight (heliotropism) and this gives them the chance catch as much sunlight as possible. Yet, when they grow in sunny places, the plants protect themselves against too much and too intense sunshine with red pigments and the green parts of the plants turn red!
The plants are extremely adaptable and grow in moist and drier places, in full-shade and full-sun. It grows from sea level up to mountainous regions. It is an annual and biennial plant that grows up to 50 cm in length.
Because Herb Robert is so adaptable it poses not only a threat to wild native plants but it can become a significant garden pest as well! So, if you have it in your garden you can keep it in control by hand-pulling them regularly. They are quite easy to hand-pull because their roots are shallow and have only little structure. What also helps to avoid them to become rampant is to mow them early in the season.
Geranium Robertianum has pretty little pink flowers that have 5 radial symmetric petals. The petals are about 5 to 7 mm long. They bloom from April to autumn. After blooming they grow distinct long and thin fruits that contain the seeds. The shape of the fruit is the source for the common name of the geranium plants: cranesbills.