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Whether you’re starting a new raised bed or refreshing an old one, what you put at the bottom matters. The right combination of materials can improve drainage, enrich the soil, and help your plants thrive. But filling a bed from top to bottom can get expensive fast.
The goal is to create a nutrient-rich growing environment that holds moisture well without becoming soggy. Below, you’ll find simple and budget-friendly ways to fill your raised garden bed—and get great results without overspending.
Wood Chips
A layer of wood chips can be used as mulch around ornamental plants in raised beds, helping retain moisture, suppress weeds, and improve the quality of the soil beneath.
Rocks, Stones, and Gravel
Place rocks and large stones at the base before topping up with compost to improve drainage, especially in areas with heavy clay soil.
Pre-Mixed Raised Bed Soil
Filling your raised beds with pre-mixed store-bought soil is likely the simplest and easiest way to fill the bottom of the garden bed. This is widely available at garden centers and typically contains a blend of topsoil, compost, and other amendments, making it ideal for raised beds.
While this is the simplest option, large volumes of pre-mixed raised bed soil can be prohibitively expensive and difficult to transport.
DIY Soil Mix
A cheaper way to fill raised beds is to make your own soil mix, since the individual components are often sold at much lower prices.
Aim for equal volumes of good-quality topsoil and well-rotted organic compost, and add any of the soil amendments listed below to boost nutrients and improve drainage.
Newspaper
A few layers of newspaper can be a weed barrier at the bottom of your raised bed. Wet the sheets as you lay them down to keep them in place and help them begin to break down. Over time, the newspaper decomposes into the soil while smothering weeds and retaining moisture.
Cardboard
Similar to a newspaper, cardboard works well to fill new raised beds. Lay down flattened boxes. Remove the tape and stickers. This sturdy layer helps suppress grass and weeds from below while eventually breaking down into organic matter.
DIY Compost
Making compost takes time, but the result is a rich, nutrient-dense organic material that guarantees fantastic plant growth.
Mix kitchen scraps and garden waste in a pile or a bin, turning it regularly to speed decomposition. When the mix resembles dark brown soil, it is ready to use as a top-up for your raised beds.
Garden Soil
Soil from your garden can be used to fill raised beds, but it should be mixed with compost to improve fertility and drainage.
Garden soil often contains a vast amount of weed seeds, so use a layer of cardboard on the surface, topped with good-quality organic compost, to prevent them from germinating.
Straw Bale Method
I love the straw bale method—it is simple, low-cost, and incredibly effective! Simply line the base of your raised bed with straw bales, using loose straw to fill in any gaps.
Water thoroughly to kick-start decomposition, then top with compost before planting.
Composted Animal Manure
Once completely decomposed, animal manure is a nutrient-rich growing medium that can be mixed with topsoil to fill raised beds.
Farmers and horse owners are a great source of low-cost manure, and – if you’re lucky – it may already be composted and ready to use. You can also buy animal manure at garden centers or online.
Grass Clippings
Grass clippings can be added to raised beds in thin layers or mixed into the soil to increase organic matter content. Never add grass clippings in a thick layer, as they can turn sludgy and inhibit plant growth as they decompose.
Biochar
Biochar, a waste product created by burning woody material at high temperatures, is an effective way to bulk out raised bed soil. This incredible substance will improve both drainage and moisture retention as well as boost microbial activity in the soil.
Biochar can be purchased online or from specialist manufacturers. You can even try making biochar using prunings from trees and bushes.
Vermiculite and Perlite
Have you ever spotted tiny white particles in the potting soil mix? This will be vermiculite or perlite, both of which can be mixed into raised bed soil at a ratio of up to 1:10 to improve aeration and drainage.
Coconut Coir
Coconut coir is a sustainable alternative to peat moss, boosting organic matter and enhancing moisture retention. Coconut coir is typically supplied in compressed blocks that can be rehydrated and mixed with soil.
Worm Castings
Worm castings are packed full of nutrients and can help supercharge your raised bed soil mix. Worm Castings can be purchased online or from most garden stores. You could also set up a vermicompost system at home.
Leaf Mold
Leaf mold is the perfect addition to make soft, crumbly soil that holds water like a sponge. Collect fallen leaves in the fall and let them decompose thoroughly before adding them to your raised beds.
Shredded Paper
Recycling your old mail or printer paper can be as simple as running it through a shredder and using the shredded material to enrich your garden. Shredded paper helps create a soft, breathable bottom layer that holds moisture and suppresses weeds.
