Can I use potting soil to start seeds?
Written by
Olivia Mitchell
Reviewed by
Prof. Charles Hartman, Ph.D.Choosing a suitable growing medium can be the difference between seed-starting success and failure. Potting soil can cause problems for delicate seedlings, and special seed-starting mixes offer ideal properties. The choice you make will directly affect germination rates and health during initial growth stages.
Seed-Starting Mix Advantages
- Sterile composition: Eliminates fungal pathogens causing damping-off
- Fine texture: Allows delicate root penetration without resistance
- Moisture balance: Retains water without waterlogging delicate roots
- Proper aeration: Maintains oxygen levels essential for germination
Potting Soil Risks
- Pathogen presence: May contain Pythium and Rhizoctonia fungi
- Coarse texture: Creates air pockets drying tiny roots
- Nutrient imbalance: Excessive fertilizers burn emerging seedlings
- Compaction issues: Hinders root development in dense mixtures
Seed-starting mixes consist of sterile mixes, which help to prevent fatal damping-off disease. This fungal disease can kill seedlings in just a few days by causing the stem to rot off at the soil line. Commercial mixes are heat-treated, and pathogens are eliminated, whereas garden soil and potting mixes can carry these pathogens, even in warm indoor conditions.
The fine texture of the seed-starting medium allows for delicate root growth. Young roots can "burst" through the surface without encountering large wood chips typically found in potting soils. This promotes better root systems that can readily absorb nutrients after they develop true leaves.
Make a DIY seed-starting mix safely. Combine equal parts coir and perlite. Bake garden soil at 180°F (82°C) according to the guidelines for 30 minutes beforehand. Afterwards, sift through the fine mesh to remove clean trash. This closely replicates the same properties as commercial mixes at a lower cost while ensuring safety.
When the seedlings have developed 4-6 true leaves, begin transitioning them to potting soil. Begin mixing the seed starting mixture and potting medium at a 1-to-3 ratio, then slowly increase the amount of potting medium over the next 7 days. This allows the seedlings to acclimate their roots to additional nutrients. Do not use fertilizer until the seedlings are established in the new container.
Read the full article: When to Start Seeds Indoors: Ultimate Guide
