Desert cacti are a challenge to get to bloom indoors, simply because we cannot provide as much light as a sun-drenched desert. In addition to light, two other important factors for blooming are:
1. Age: Some plants take years to mature. The best way to check this is to buy one already blooming.
2. 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) with plenty of sunlight.
Also, keep in mind these five tips for year-round cactus care:
1. Indoor cacti do best in a sunroom because they will receive the most sunlight, and the air around windows is generally cooler in winter than in the interior of a room.
2. Your cactus needs maximum light and heat during the growing season. Put your plant in direct sunlight, and turn it occasionally for even light exposure.
3. It will also need more water during the growing season. Allow the top 2 inches (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.
4. Fertilize cacti only in the spring and early summer, using a cactus-specific fertilizer or a highly diluted fertilizer lower in nitrogen and higher phosphorus and potassium. Overfeeding will not make your cactus bloom!
5. Repot your cactus using a potting mix designed for cacti and succulents. Do not water your cactus for a week after repotting.
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