How to Fill a Raised Bed Cheaply – DIY Guide
Fill a raised bed cheaply by layering coarse material at the base — logs, cardboard, garden waste — then topping with a mix of topsoil and homemade or bagged compost. This hugelkultur-inspired method cuts the volume of expensive topsoil needed and improves drainage and fertility over time.
- Wheelbarrow
- Garden fork
- Spade
- Hose or watering can
- Tape measure
- Gloves
- Cardboard (unpainted, uncoated)
- Logs, branches or wood chip
- Garden waste and leaves
- Topsoil
- Homemade or bagged compost
- Straw or wood chip mulch
- Well-rotted manure (optional)
Step-by-Step Guide
Measure your raised bed volume
Calculate the internal dimensions of your raised bed (length × width × depth in metres) to work out the volume in cubic metres. A typical 1.2 m × 2.4 m bed at 40 cm deep holds roughly 1.15 m³ — knowing this prevents you buying too much or too little material. Even if you already have your raised bed built cheaply, measure again before ordering fill.
Lay a cardboard base
Cover the ground inside the bed with a double layer of unpainted, uncoated cardboard, overlapping edges by at least 15 cm. This suppresses weeds from below, breaks down within one growing season, and draws in earthworms that improve soil structure. Remove any tape or staples before laying.
Fill the lower third with bulky organic material
Pack the bottom third of the bed with logs, thick branches, wood chip, or spent plant material. Smaller, partially rotted wood breaks down faster and releases nutrients sooner — this is the core principle of hugelkultur filling. Avoid diseased plant material, any wood treated with preservative, or persistent weeds such as couch grass or bindweed. This bulk layer dramatically reduces the volume of topsoil you need to buy.
Add a middle layer of compost and garden waste
Fill the next third with a mix of homemade compost, autumn leaves, grass clippings, and any well-rotted manure you can source cheaply or for free from a local stable or farm. This layer acts as the nutritional engine of the bed as it continues to break down, feeding roots from below. The Garden Guide covers soil health and composting in more detail if you want to go deeper.
Top with a quality growing medium
Fill the final third — the top 15–20 cm — with a blend of topsoil and compost in roughly a 50:50 ratio by volume. This is the only layer plant roots need to establish in initially, so quality matters here even if cost-cutting is the goal. Avoid pure topsoil alone, which can compact and drain poorly; compost keeps the structure open. Water the whole bed thoroughly once filled so all layers begin to settle and knit together. For guidance on keeping your wider garden productive, see our advice on how to feed and weed a lawn as part of a wider garden maintenance routine.
Top-dress and mulch the surface
Once planted, apply a 5 cm layer of straw or wood chip mulch across the surface. Mulch reduces moisture loss, suppresses weeds, and adds further organic matter as it breaks down — extending the value of the cheap fill below. Expect the bed to sink 5–10 cm over the first growing season as organic material compresses; top up with compost the following spring.
Frequently Asked Questions
How much topsoil do I actually need to fill a raised bed?
Using the layering method, you only need topsoil for the top 15–20 cm of the bed. For a standard 1.2 m × 2.4 m bed, that is roughly 0.35–0.58 m³ of topsoil — approximately half of what you would need if filling the whole bed with bought soil.
Can I use garden soil to fill a raised bed?
You can use garden soil as part of the blend, but using it alone is not recommended — it compacts in containers, drains poorly, and can introduce weed seeds and soil-borne disease. Always mix it at least 50:50 with compost for the top growing layer.
What wood should I avoid putting in a raised bed?
Never use timber that has been treated with preservative, painted, or pressure-treated, as these can leach harmful compounds into the soil. Also avoid wood from black walnut, which produces a natural compound called juglone that suppresses many vegetable crops. Building your raised bed cheaply covers suitable timber choices in more detail.
Where can I get free or cheap fill material in the UK?
Local stables and farms often give away well-rotted horse manure for free or very cheaply. Council green waste composting sites sometimes sell bulk compost at low cost. Fallen leaves bagged in autumn, spent compost from last season’s pots, and cardboard from deliveries are all genuinely free sources. Seeding a bare lawn also involves topsoil topdressing, so leftover material from lawn projects can be repurposed.
How long before the bottom layers break down fully?
Smaller branches and garden waste break down within one to two growing seasons. Larger logs take three to five years. During that time they act as a moisture reservoir and slow-release nutrient source — the bed actually improves year on year as the material decomposes.
Wet each layer as you build — especially the wood and cardboard — before adding the next. Dry organic material wicks moisture away from roots rather than retaining it, and a bone-dry base layer can take an entire season to start breaking down properly.
Sources
- RHS — Raised beds: how to make and fill them — rhs.org.uk
- RHS — Compost: making garden compost — rhs.org.uk
- Which? — How to make a raised bed — which.co.uk
This guide is for general information only. Always work safely and follow manufacturer instructions. DIYnut accepts no liability for injury or damage arising from DIY work.
