Whenever handling barrel cactus, it is important that you take precautions not to injure yourself, as these plants have big needle-like thorns. You can wrap a lot of newspaper around the cactus, and use hand gloves when handling these plants.
Buying and Propagating: One can easily get the cactus plants or seeds from plant nurseries. If it freezes outside during winters in your area, keep your barrel cactus indoors.
Light Requirements: Barrel cactus needs full exposure to the sun. If you have a houseplant, keep it near a window, where it can get plenty of light. Barrel cacti usually grow towards the south direction for preventing sunburn, this behavior gives them the name 'compass cactus'. So, keep turning your plant, because sometimes, when it is leaning towards the direction of the south, it might tip over. If the barrel plant leans too much on one side, gently place it in the center again.
Humidity and Temperature Maintenance: This cactus usually grows in areas like under the desert canyon walls, along desert washes and gravely slopes. It prefer a dry, warm, and well-ventilated surrounding. So, maintain dry and low humidity area when caring for barrel cactus. Maintain a temperature between 45ºF to 80ºF.
Soil Requirements: Cactus prefer moist soil, and sometimes, rot in wet soil conditions. To prepare a soil mixture for barrel cactus, sterilize a commercial soil mixture in the oven at 180ºF for 30 minutes. Then, add 2 parts of this commercial soil mix with 1 part of gravel or sand, and add perlite. Cactus need well-drained soil, the above soil mix will maintain the plant in a good condition.
Potting Instructions: You can use a small containers or clay dishes, for small-sized barrel cactus, and big pots for the larger varieties. Always keep in mind that the size of the pot should be larger than that of the root ball by at least few inches for container gardening.
Watering Instructions: Barrel cacti don't need to be watered often. Excess watering causes it to rot. Water the houseplant once in a month. You can check the time by sticking a wooden stick or pencil in the pot soil, if damp soil is on the stick, do not water the plant. When you find dry soil on the stick, you can give water to the plant. You can use this stick technique for other cacti too.
Fertilization: If you have golden barrels, use high phosphorus fertilizer for care of cactus plants. Most cacti need nitrates, so you can buy plant food, which contains nitrates, from a nursery. You can add this fertilizer to the plant 3 times in a year, during spring, summer, and autumn.
Pests and Problems: Sometimes, pests can attack the cactus. The best way to prevent any pests is to change the soil regularly and use a good soil mix. Excess watering, as you already know, can cause rotting, so take special care when watering the plants.
Watering once a month and maintaining good soil and light conditions, are the most important factors when maintaining barrel cactus. If you follow these instructions, you can grow barrel cactus for years in your house, and, may be some day, even get to see the lovely flowers and fruits on these plants!