One of the tallest, Ageratum houstonianum 'Blue Horizon' (Floss Flower) is a frost-tender annual boasting fluffy lavender to purplish-blue flower clusters, up to 3 in. across (7 cm), from late spring to frost. Attractive to butterflies, the blossoms are borne on long, sturdy stems and float above the neat foliage mound of heart-shaped leaves. Best used for edging or borders of beds or in containers. Great for cutting.

• Recipient of the prestigious Award of Garden Merit of the Royal Horticultural Society.
• Grows up to 18-30 in. tall (45-75 cm) and 12-18 in. wide (30-45 cm)
• Performs best in full sun in rich, moist, well-drained soils. Appreciates some light afternoon shade in hot summer climates. Provide consistent moisture throughout the growing season.
• Excellent choice for beds and borders, edging, city gardens, cottage gardens.
• No serious pest or disease issues. Root rot may occur in poorly drained soils. Deer and rabbit resistant.
• Propagate by seed. Easily grown from seed, starting indoors in late winter and transplanting outdoors after the danger of frost has passed. Alternatively, seeds can be sown in the garden after the last frost date.
• Ageratum houstonianum species is native to Mexico and Central America. It is reported to be a weed and invasive outside its native range, due to its high production of small seeds with easy dispersal by wind or water. It is reported invasive in Australia and South Africa and neighboring countries (Swaziland, Mozambique and Zimbabwe) where it poses a threat to biodiversity.