How Much Biochar Do I Need? A Rough Guide.

Use this quick guide to work out roughly how much Sweethill Biochar you need. Please note that there is no one magic number when it comes to using biochar, because every base soil and environment is different. The good news is that even a little biochar goes a long way, and it’s not possible to add too much, so there’s no way you can get it wrong! From my own experience of growing veggies in my garden with our biochar, I always find that more is more, and being generous with your soil is only ever going to lead to good things.

The Simplest Rule

If you don't want to calculate anything:

For large areas: 5–10 L per m²

For compost and potting mixes: 5–10% by volume

For individual plants: approximately one handful as you plant.

Always wet and charge Sweethill Biochar before use. Never apply it dry.

You don't need to add huge quantities all at once. Biochar is a long-lasting soil amendment, so you can gradually build it into your soil over several seasons.

  • As an easy starting point, use approximately 5–10 litres of biochar per square metre when incorporating it into the upper 10 cm of soil.

    1 m² = 5–10 L biochar
    5 m² = 25–50 L
    10 m² = 50–100 L
    25 m² = 125–250 L
    50 m² = 250–500 L

    You don't need to treat the whole area at once. Biochar can be added gradually as you plant, mulch or improve individual sections.

  • For Pots, Containers & Growing Media

    Use approximately 5–10% biochar by volume.

    To calculate:

    Litres of growing medium × 0.05 = 5% biochar
    Litres of growing medium × 0.10 = 10% biochar

    So:

    10 L compost = 0.5–1 L biochar
    25 L compost = 1.25–2.5 L biochar
    50 L compost = 2.5–5 L biochar
    100 L compost = 5–10 L biochar

  • For Hanging Baskets

    Use approximately 5–10% of the finished growing mix.

    A typical:

    10 L basket = 0.5–1 L biochar
    15 L basket = 0.75–1.5 L biochar
    20 L basket = 1–2 L biochar

  • For Individual Plants

    A simple alternative to measuring is our handful method.

    For a vegetable seedling, perennial or small plant:

    About 1 handful of charged biochar per planting position.

    Mix it with the compost or soil around the rootball.

    For larger shrubs:

    Several handfuls, mixed through the surrounding planting soil.

    For trees:

    Use a larger quantity appropriate to the rootball and planting area, distributing charged biochar around the rootball where new roots will grow.

  • For No-Dig Beds

    Mix biochar through the compost you're applying to the surface.

    A straightforward starting point is:

    5–10% biochar within the compost being applied.

    So if you're spreading:

    100 L compost → mix in 5–10 L biochar.

    There is no need to dig it into the underlying soil.

  • When preparing a new lawn, use approximately:

    5–10 L biochar per m², mixed through the upper soil during ground preparation.

    For established lawns, use smaller quantities mixed into a suitable top-dressing, ideally after aeration, rather than applying biochar directly to the grass.

  • For Compost Heaps

    There's no need for precise measurement.

    Add small amounts regularly as you build your heap, distributing the biochar throughout the composting material rather than creating thick layers.

    The composting process is also an excellent way to charge the biochar before it reaches your soil.