First-year seedlings develop into rosettes. Maximum root growth occurs in this stage. Plants that have wintered in the rosette stage, bolt in May or June and most bud by mid-June. Flowering occurs in July and August with mature seeds being formed by mid-August. Shedding of the seed occurs immediately, and if moisture is adequate, the seeds will germinate and develop into rosettes by fall.
Knapweed tends to be a long-lived biennial plant producing seeds for two or more years.
The old stalks remain throughout the winter and that is one of the easiest times for identification and infestation assessment.