Start with a soil mix, not pure topsoil

Fill your raised bed with a mixture of materials rather than topsoil alone. Pure topsoil compacts over time, drains poorly, and leaves plants struggling for water and nutrients. A layered or blended approach gives you better drainage, aeration, and long-term structure.

The most common method is the "lasagna" or layered approach: start with coarse materials at the bottom (branches, cardboard, wood chips), add a layer of compost or aged manure in the middle, and finish with topsoil mixed with compost on top. This creates air pockets and breaks down gradually to feed your plants. Alternatively, you can blend everything together before filling—mix topsoil, compost, and peat moss or coconut coir in roughly equal parts, then shovel it all in at once.

Key Takeaways

  • Layer coarse materials at the bottom to improve drainage and create air pockets that roots need.
  • Mix topsoil with compost and peat moss or coconut coir rather than using topsoil alone, which compacts and drains poorly.
  • Fill the bed to within 2 inches of the rim so soil settles without spilling over the edge.
  • Water the bed thoroughly after filling to help materials settle and reveal low spots that need topping off.
  • Expect the bed to settle 4 to 6 inches over the first year as organic materials break down.

Layer the bottom for drainage and structure

The bottom layer prevents water from pooling and gives the soil room to breathe. Use materials that break down slowly: branches, twigs, wood chips, or shredded leaves. Aim for 3 to 6 inches depending on your bed depth. If your raised bed sits directly on soil (not on a hard surface), this layer is less critical but still helpful.

If you want to block weeds from growing up into the bed, lay cardboard or newspaper over the bottom layer before adding compost. Wet the cardboard so it stays in place, then overlap the pieces by at least 6 inches. The cardboard will decompose over one to two years, but by then your soil will be established enough that weeds are less of a problem.

Add compost and aged manure in the middle

This layer feeds your plants as it breaks down. Use finished compost (dark, crumbly, earthy-smelling) or well-aged manure from horses, chickens, or cows. Fresh manure will burn plant roots and should sit for at least six months before use. Aim for 2 to 4 inches of this layer.

If you are building in spring and do not have finished compost yet, you can use partially decomposed material—it will continue breaking down as your plants grow. Avoid manure from pets or meat-eating animals, which can carry harmful pathogens. If you are unsure whether your compost is finished, it should be cool to the touch and smell like soil, not like ammonia or rotting food.

Top with a soil and compost blend

The top 6 to 8 inches is where your plants will spend most of their time, so this layer matters most. Mix topsoil with finished compost in a 1:1 ratio, or use a commercial raised-bed soil mix. If your topsoil is heavy clay, add peat moss or coconut coir (about 20 percent by volume) to improve drainage and prevent compaction.

Fill to within 2 inches of the rim. The bed will settle as materials decompose and water moves through it, so leaving space prevents overflow when you water. After the first watering, you may see the level drop noticeably—this is normal. Wait a few days, then top off with more soil if needed.

Water thoroughly and let it settle

After filling, water the entire bed slowly and deeply until water runs out the bottom. This helps materials settle into place and reveals any low spots. The bed may drop 2 to 4 inches when ready after the first watering. Wait a day or two, then add more soil to bring it back to 2 inches below the rim.

If you are filling in spring and planting right away, water again the day before you plant. If you are filling in fall or winter, water once and let it sit. The materials will continue settling over weeks and months as rain and time do their work.

Plan for settling over the first year

Expect the bed to drop another 2 to 6 inches over the first growing season as organic materials break down and compress. This is not a problem—it means your soil is becoming richer. In spring of the second year, top off the bed with 2 to 3 inches of fresh compost to restore the level and add nutrients.

After the first year, you will only need to add 1 to 2 inches of compost annually to maintain fertility and height. The bed will eventually stabilize at a lower level than it started, but the soil will be darker, richer, and easier to work with than when you began.

Adjust for your climate and water situation

In dry climates, use less peat moss or coconut coir (which dry out quickly) and more compost, which holds moisture longer. In wet climates or if your bed sits in a low spot, add extra coarse material at the bottom and consider raising the bed higher to improve drainage.

If you are filling a very large bed, calculate volume before you buy materials. A 4-by-8-foot bed that is 12 inches deep holds about 32 cubic feet of soil. Most bagged soil is sold in cubic feet, and bulk soil is sold by the cubic yard (27 cubic feet). Knowing this ahead of time saves trips to the garden center.

Frequently Asked Questions

Can I use just compost without topsoil?

You can, but it is not ideal for the long term. Pure compost drains too fast and settles heavily after the first year. Mix it with topsoil or a soil-like material (coconut coir, peat moss, or aged bark) so the bed holds moisture and structure better.

What if I do not have a bottom layer—will weeds grow through?

Weeds can grow up from soil below the bed, especially if the bed sits on lawn or bare ground. A cardboard or newspaper layer stops most of them. If you skip this step, you will likely pull weeds from the bed for the first year or two, but fewer as your soil deepens and shades the ground below.

How much does it cost to fill a raised bed?

Cost varies by location and material quality. A 4-by-8-foot bed 12 inches deep typically costs between $40 and $150 in materials, depending on whether you use bagged soil (more expensive, easier to transport) or bulk soil (cheaper per cubic foot but requires delivery). Compost and aged manure are often free or very cheap from local sources.

Can I reuse soil from last year?

Yes. Remove the top 2 to 3 inches (which may be compacted or depleted), then mix the rest with fresh compost before refilling. This saves money and is better for the soil structure than starting completely fresh.

Should I add fertilizer when I fill the bed?

If you use finished compost and aged manure, you do not need to add fertilizer at planting time. The compost provides enough nutrients for the first few weeks. After that, side-dress with compost or use a balanced fertilizer as plants grow, depending on what you are planting.