Also, be sure to keep an eye on our Succulent City Youtube channel! Growing cactus requires patience. But it is also about being patient and keeping an eye out for potential problems. When you plant your barrel cactus outdoor, things will change. You should use a balanced fertilizer every other month if the plant's growth is ongoing. If the plant was placed indoors, it is better to let it stay outdoors to get enough sunlight. Once they have grown up indoors, they will need to be exposed to sunlight outside.