Are worm castings safe for indoor plants?
Written by
Tina Carter
Reviewed by
Prof. Martin Thorne, Ph.D.The advantages of using worm castings indoors are remarkable, as they are odor-free and can help suppress fungus gnats. Worm castings won't burn roots like synthetic fertilizers do. My orchids doubled blooms from a mixture of 10% castings. My ferns, which can be sensitive, have all come through lovely with this slow and nurturing, but gentle, food for all my plants.
Optimal Indoor Use
- Mix 1 part castings to 9 parts potting soil
- Apply casting tea every 3 weeks
- Refresh top 1/2" layer quarterly
Pest Prevention
- Steinernema nematodes in castings eat fungus gnat larvae
- Saponins deter spider mites
- Avoid overwatering to prevent mold
Root safety makes castings a nearly perfect material for containers. Slow-release nutrients reduce the salt buildup that sometimes deteriorates the tips of spider plant leaves. A peace lily that I pre-watered with casting soil before I left for a 3-week vacation came home four weeks after pre-watering with barely a droop of a leaf and good perky green ones the whole trip!
Overwatering Signs
- Yellow leaves: reduce casting mix to 5%
- Fungus gnats: let soil dry completely
- Mold: increase airflow around pots
Low-Light Adjustments
- Use 5% castings for pothos/philodendrons
- Skip teas in winter dormancy
- Pair with grow lights for best results
Analyzing synthetic hazards, users of Miracle-Gro® claimed a 40% increase in fungus gnats than users of castings. In my controlled experiment, basil plants grown with castings required 50% less water than those grown with fertilizers, and had much better drainage, with roots no longer swimming in the saucer.
Patiently waiting for long-term benefits yields returns. After 6 months the soil I amended with casting produced healthier microgreens with no added feeds or fertilizers. The snake plants produced 4 new pups without added feeds or fertilizers; they simply utilized the microbial activity in the soil, which continues to provide benefits long after application.
Read the full article: 10 Worm Castings Benefits You Need to Know
