Life cycle

Spotted knapweed rosette

Spotted knapweed rosette

The spotted knapweed is a short-lived perennial, which means that an individual plant can live for several years, but does not usually live beyond a certain age. The spotted knapweed has an average life span of 3 to 5 years, but can live up to 9 years.

The spotted knapweed starts as a seed, then becomes a rosette, and finally becomes a flower. Although the name rosette suggests that this plant stage is a flowering stage, it is not.

Definition: A rosette is a circular cluster of leaves that radiate from a center at or close to the ground, as in the dandelion.

In the beginning, there was a seed

Spotted knapweed plants start from seed. These seeds can germinate in the fall or spring, but fall germinators don't usually survive through the winter. The seeds germinate into rosettes.

Then came the rosette

The seeds which germinate into rosettes remain rosettes for the first growing season. The following spring, the rosettes can either remain rosettes, or they can become flowering plants.

And finally, the flower

Flowering spotted knapweed

Spotted knapweed flower

Once the rosette becomes a flower, this spotted knapweed plant remains a flower until it dies. This flower stage is the seed producing stage.

Flowering plants produce about 8-15 flowering heads per plant, and each of these flowering heads each produce about 12-74 seeds. This means a single flowering plant can produce anywhere from about 72 to 1110 seeds. This number of seeds produced depends on environmental factors such as site condition and precipitation.

The seeds produced by the flower disperse from the plant when it dries out in late summer, at the end of the growing season. Since the seeds are quite heavy, they don't disperse very far from the plant. Once the seeds do disperse, they can remain in the soil for up to 8 years.