Seed starting mix vs garden soil
UConn says garden soil is not recommended for container plants, because it will compact quickly with repeated watering.
What to use
- UConn says to use packaged potting media or soilless mixes. Soilless mixes are lightweight and usually sterilised, and finer-textured ones are sold for starting seeds.
- Oklahoma State says to use a well-draining seed starting mix with perlite for drainage and peat moss for moisture retention.
- Cornell Monroe says to use good quality potting soil from a garden store, and does not mention a specialised mix. The sources are not identical.
What the ingredients do (UConn)
| Ingredient | Role |
|---|---|
| Peat moss | Main component of many soilless mixes |
| Sphagnum moss | Often used in seed starting mixes because it resists fungus |
| Perlite | Improves drainage and aeration; sterile |
| Vermiculite | Holds moisture and nutrients, and slowly releases some potassium, magnesium and calcium |
| Coarse sand | Adds drainage and weight; use only washed or horticultural grade |
| Bark | Cheaper peat alternative with better aeration, but dries faster |
Using it
- Moisten the mix before filling containers, with warm water, until it is damp like a sponge and does not drip (Oklahoma State). UConn says dry organic material repels water.
- Starter fertiliser in a mix runs out, so plants need regular feeding later (UConn). See fertilising seedlings.
- pH for soilless media is about 5.5 to 6.0 (UConn).
Damp, sterile mix also helps against damping-off. See fans and damping-off.
Sources
- UConn Home & Garden Education Center: Potting media (PDF)
- Oklahoma State University Extension: Tips for starting seeds at home (2025)
- Cornell Cooperative Extension, Monroe County: Starting vegetables from seed