Maintaining Mammillaria plumosa, or the Feather Cactus, involves specific care to ensure its well-being and promote its unique features. Here’s a brief guide:

1. Light: Provide bright, indirect sunlight or partial sunlight. Mammillaria plumosa thrives in well-lit conditions, but protection from intense, direct sunlight is advisable to prevent sunburn.
2. Watering: Allow the soil to dry out between waterings. Water sparingly, especially during the dormant winter months. Overwatering can lead to root rot, so it’s crucial to let the soil dry before watering again.
3. Soil: Plant the Feather Cactus in well-draining cactus or succulent soil. A mix that includes sand or perlite can enhance drainage and prevent waterlogged conditions.
4. Temperature: Maintain warm temperatures, and protect the cactus from frost. Feather Cactus is sensitive to cold temperatures, so it’s essential to shield it from freezing conditions.
5. Fertilization: Feed with a diluted, balanced cactus fertilizer during the growing season (spring and summer). Avoid fertilizing during the dormant period in winter.
6. Pruning: While not extensive pruning is needed, you can remove any dead or damaged spines or offsets to maintain the cactus’s appearance.
7. Pest Control: Watch for common cactus pests such as spider mites or scale insects. Treat any infestations promptly with insecticidal soap or neem oil.
8. Potting: Repot when necessary, typically every 2-3 years, using fresh cactus soil. Ensure the new pot has drainage holes.

Observing your Mammillaria plumosa regularly will help you understand its individual needs. Adjust care based on the specific conditions of your growing environment, and enjoy the unique beauty of this feather-like cactus.