It is rarely kept as a houseplant , but a 50-year-old blue agave in Boston grew a 30-foot (9 m) stalk requiring a hole in the greenhouse roof and flowered in the summer of 2006. Feed the blue agave in early spring when new growth is evident. Give it a half-strength dose of liquid fertilizer for cacti and succulents. Do not overfeed this plant. Fertilizer encourages flowering, which signals the end of the blue agave’s life cycle.