Desert cacti are a challenge to get to bloom indoors, simply because we can’t provide as much light as a sun-drenched desert. In addition to light, two other important factors for blooming are:
- Age: Some plants take years to mature. The best way to check this is to buy one that’s already blooming.
- Dormancy: Many desert cacti bloom in response to a cool, dry, dormant period. During the winter, you should reduce watering to only about once a month—just enough to keep the plant from shriveling up—and move your cactus to a cool spot, around 50°F (10°C), that has plenty of sunlight.
Also, keep in mind these tips for year-round cactus care:
- Indoor cacti do best in a sunroom or south-facing windowsill. They’ll receive the most sunlight, and the air around windows is generally cooler in winter than the interior of a room.
- During the growing season, your cactus needs maximum light and heat. Put your plant in direct sunlight, and turn it occasionally for even light exposure.
- It will also need more water during the growing season. Allow the top 2 inch (5 cm) of soil to dry out before watering the plant thoroughly until it runs out the bottom (empty the drainage tray). Imagine a sudden desert rainstorm that soon dries in the sun, so never leave your plant in soggy soil.
- Fertilize cacti only in the spring and early summer, using a cactus-specific fertilizer or a highly diluted fertilizer lower in nitrogen and higher in phosphorus and potassium. Overfeeding will not make your cactus bloom!
- Repot your cactus using a potting mix designed for cacti and succulents. Don’t water your cactus for a week after repotting.
