Seed Compost & Module Trays

Sowing

The right compost and container make sowing more reliable. Fine peat-free seed compost gives small seeds close contact with an even, low-nutrient medium, while module trays keep individual roots separate. They are especially useful for plants that resent disturbance, and make spacing, watering and planting out much easier to manage.

How to do it

Use fresh peat-free seed compost, or a fine peat-free multipurpose compost sieved for very small seed. John Innes seed compost is another suitable option where available. Fill clean module trays evenly, tap them to settle the compost and level the surface without compacting it. Water before sowing if the compost is dry. Place one or two seeds in each module, then cover to the recommended depth. After germination, remove the weaker seedling if two have emerged. Water from below or with a fine rose, allowing surplus water to drain away. When white roots hold the plug together but have not circled densely, plant it out or pot it on with minimal disturbance.

When to do it

Prepare modules whenever a crop is best started under cover, generally from late winter through spring. Larger modules suit plants that will remain indoors for several weeks, while smaller cells suit quick crops. For autumn planting, sow hardy salads and some flowers in late summer when greenhouse temperatures are less extreme.

Tips

Peat-free compost can dry at the surface while remaining wet beneath, so check moisture with a fingertip before watering. Use trays with drainage holes and set them in a watertight base only briefly. Do not reuse old seed compost. Choose cell sizes to suit the expected growing period, rather than filling oversized modules unnecessarily.

Seed Compost & Module Trays: frequently asked questions

How does seed compost & module trays work?

Use fresh peat-free seed compost, or a fine peat-free multipurpose compost sieved for very small seed.

When should I do seed compost & module trays?

Prepare modules whenever a crop is best started under cover, generally from late winter through spring.

What are some tips for seed compost & module trays?

Peat-free compost can dry at the surface while remaining wet beneath, so check moisture with a fingertip before watering.

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General guidance for UK gardens. Page updated 19 Sep 2026.