Best Seed Starting Soil Mix

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The mix you use matters as much as the tray. Seeds and tiny roots need something light, fine and clean, which is not the same as garden soil or all-purpose potting soil.

Seed starting mix vs potting soil vs garden soil

• Seed starting mix: fine, light and drains well. It is usually soilless and sterile, so it is less likely to carry weed seeds or disease.
• Potting soil: coarser and often contains fertilizer. Better for larger plants in bigger containers. Some gardeners use it for seed starting, but the texture can be heavy for tiny seedlings.
• Garden soil: not recommended. It compacts in a tray, drains poorly and may bring weeds, pests and disease indoors.

What is in a good mix

• Peat moss or coconut coir holds moisture and makes the mix soft.
• Perlite adds air space so roots can breathe and water can drain.
• Vermiculite holds moisture and nutrients and keeps the mix evenly damp.

A simple DIY recipe

A commonly used home recipe is equal parts peat moss or coir, vermiculite and perlite. Mix it dry in a bucket (wear a mask, as the dust is unpleasant), then add water slowly until it feels like a wrung-out sponge.

Peat or coir?

Both work. Peat is acidic and a standard ingredient in many commercial mixes. Coir is made from coconut husks and some gardeners prefer it for sustainability reasons. If you use coir, choose a product that is washed or buffered, since unwashed coir may contain salts.

What to check on the label

• It says "seed starting" or "seed starter" mix.
• The texture is fine, with no large sticks or bark chunks.
• It is not loaded with heavy fertilizer, which can burn young roots.