Seed Starting Mix and Trays

Why not just use garden soil?

Garden soil is heavy, drains poorly in small containers, and can carry weed seeds, insects and disease organisms. Seedlings have tiny roots and little defense, so a clean, fine, light mix gives them a better start.

Seed starting mixes are designed to hold moisture while letting air reach the roots. They usually contain little or no soil and are low in nutrients, which is fine for the first weeks.

Check the bag description, since products vary, and ask your extension office what works well in your area.

What goes into a good mix?

Common ingredients include peat or a substitute such as coir, along with perlite or vermiculite for drainage and moisture. Some mixes add small amounts of compost or fertilizer. Fine texture matters, because small seeds need good contact with the mix.

Moisten the mix before filling trays, since dry peat repels water. Mix in a tub with warm water until it feels like a wrung-out sponge, then fill the cells and press lightly. Store unused mix dry and closed.

Different crops like different amounts of moisture holding, so a mix that suits lettuce may be a little wet for peppers. Watch how quickly your trays dry and adjust watering before you consider changing the mix.

• Light and fine texture
• Good drainage and moisture holding
• Free of weed seeds and disease
• Moistened before filling

What kind of trays and cells work best?

Trays with drainage holes, a solid tray beneath to catch water, and cells deep enough for the crop all work. Deeper cells suit crops with long roots, while small cells suit lettuce and herbs. Pots made of peat, paper or newspaper can be planted whole, though check that they break down in your soil.

Larger cells give plants more room and a longer time before they need potting up. Smaller cells use less mix but dry out faster and need watering more often.

Cell size also controls how soon you must pot up. Crops that stay indoors for many weeks do better in larger cells or get moved to bigger pots once roots fill the first container.

How do I clean reused trays and pots?

Remove all old soil and roots by scrubbing in warm soapy water. Rinse well, then disinfect according to guidance from your extension office, and rinse again if the instructions say so. Let everything dry before use.

Cleanliness lowers the risk of damping-off and other seedling diseases. Do not mix household cleaners, and wear gloves and work in ventilated space when using any disinfectant. Follow the label on whatever product you use.

Keep a small bucket and brush just for tray cleaning and do it in late winter before sowing, so you are not rushing on the day seeds need to go in.

How do I prevent damping-off?

Damping-off is a group of fungal problems that rot seedlings at the soil line, often after a good start. Prevent it with clean containers, fresh mix, proper drainage, gentle watering and some air movement.

Do not overwater, and avoid sowing too densely. Remove covers once seeds sprout. If a patch of seedlings collapses, take them out and let the area dry. A very thin dusting of a dry, inert material on the surface is sometimes suggested, so ask your extension office what they recommend.

Write down what you used and how seedlings did. If damping-off appears despite good habits, ask your extension office to help you troubleshoot, since the cause may be temperature, water quality or a contaminated bag of mix.

How should I water in trays?

Bottom watering lets the mix draw water up from a tray, which avoids washing out tiny seeds and wetting leaves. Pour water into the tray, wait until the surface darkens, then drain any extra.

Gentle misting works for freshly sown seeds. Always empty standing water, and check cells daily, since small containers dry quickly under lights.

What does it cost to set up?

Cost categories include mix, trays and cells, a way to hold them such as shelves, lights and a timer, a heat mat if needed, labels and a few small tools. You can reuse containers and make your own labels, which lowers cost.

Start small with one or two trays and learn what you need before buying more equipment.

Buying the largest bag of mix is not always a saving if half spoils or dries out. Ask neighbors or a gardening group about splitting supplies.

Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.