Rhubarb plants will occasionally send up flowers and seed stalks in the middle of the plants. The flowers and seed stalks can occur due to winter's chilling conditions.
Stalks can also occur due to natural maturity of the plants.
Flower and seed stalks reduce the vigor of the plant. Energy is funneled into the stalks instead of new growth. Therefore, flower and seed stalks should be cut out as soon as they start forming. However, the plant may still continue to produce the flower stalks. Plants do NOT become poisonous after flowering starts.