Start with a base layer of coarse material

The first step is to add a drainage layer at the bottom of your raised bed. This keeps water from pooling and prevents root rot. Use materials that won't compact: wood chips, straw, shredded leaves, or crumpled cardboard work well. Fill the bottom 2 to 4 inches with whichever you have on hand.

If your raised bed sits directly on soil, you can skip this step—water will drain naturally into the ground below. If it sits on concrete or a patio, the drainage layer becomes important. Aim for materials that break down slowly so they don't settle into a dense mat within a season or two.

Add a layer of compost or aged manure

On top of the drainage layer, spread 2 to 3 inches of finished compost or aged manure. This layer feeds the soil as it breaks down and improves water retention. Finished compost is dark, crumbly, and has no smell of ammonia—if it smells sharp, it's not ready yet and will heat up as it decomposes, potentially cooking plant roots.

You can buy compost in bags from a garden center, or get it in bulk from a landscape supplier if you're filling a large bed. Aged manure (at least six months old) works the same way. Fresh manure will burn plants, so don't use it unless it's been sitting for half a year or longer.

Fill most of the bed with topsoil or garden soil

The bulk of your raised bed should be topsoil or a garden soil mix—not potting soil, which is too light and expensive for large volumes. Topsoil is the dark, nutrient-rich layer from the top of the ground. A garden soil mix is topsoil blended with compost and sometimes perlite or sand to improve drainage.

Fill the bed until it's about 2 inches from the top rim. This leaves room for mulch and prevents soil from spilling over the edge when you water. If you're planting vegetables or flowers that need loose, well-draining soil, a 50-50 mix of topsoil and compost works better than topsoil alone.

For a 4-by-8-foot bed that's 12 inches deep, you'll need roughly 32 cubic feet of soil. Most suppliers sell soil by the cubic yard (27 cubic feet), so you'd order just over one cubic yard. Ask the supplier to deliver if the bed is large—a cubic yard of wet soil weighs about 1.5 tons.

Key Takeaways

  • Start with 2 to 4 inches of coarse drainage material like wood chips or straw if your bed sits on concrete or pavement.
  • Add 2 to 3 inches of finished compost or aged manure to feed the soil and improve water retention.
  • Fill the rest of the bed with topsoil or a topsoil-and-compost blend, leaving 2 inches of space at the top.
  • For large beds, buy soil in bulk from a landscape supplier rather than bags, and ask about delivery if the volume is heavy.
  • Let the bed settle for a week or two before planting, especially if you've used fresh materials that will compact as they absorb water.

Mix in amendments based on what you're growing

Before planting, consider what you'll grow and whether your soil needs adjustment. If you're planting vegetables, mix in a balanced fertilizer or a slow-release organic fertilizer according to package directions. If you're planting acid-loving plants like blueberries, add sulfur to lower the pH. If your soil is heavy clay, work in perlite or coarse sand to improve drainage.

You don't need to amend the soil if you're using a high-quality garden soil mix that already contains compost—most commercial mixes are balanced enough for general planting. Amendments matter most if you're using straight topsoil or if you know your native soil has a specific problem (too acidic, too alkaline, too dense).

Water the bed and let it settle

After filling, water the entire bed thoroughly until the soil is damp all the way through. The soil will settle over the next week or two as it absorbs water and compacts slightly. You may need to add more soil after settling to bring it back to the top rim.

Wait at least a week before planting, especially if you've used fresh compost or manure. This gives the materials time to begin breaking down and the soil temperature to stabilize. If you plant when ready into freshly filled soil, the bed may settle unevenly under your plants, leaving some roots exposed or others buried too deep.

Avoid common mistakes when filling

The most common error is using potting soil for the entire bed. Potting soil is designed for containers and costs three to five times more than topsoil. It also drains so quickly that it dries out in a raised bed, especially in hot weather. Save potting soil for pots and hanging baskets.

Another mistake is using fresh manure or uncomposted materials. Fresh manure releases ammonia as it breaks down, which burns plant roots and can make vegetables unsafe to eat. Uncomposted leaves and grass clippings will heat up as they decompose, potentially reaching 140°F or higher—hot enough to kill seedlings planted too close. Always use finished compost and aged manure.

A third error is filling the bed completely to the rim. Soil settles, and water splashes over the edge during watering. Leaving 2 inches of space prevents both problems and gives you room to add mulch, which keeps weeds down and retains moisture.

Frequently Asked Questions

Do I need to line the bottom of my raised bed?

A lining is optional and depends on what's underneath. If your bed sits on soil, you don't need one—water drains naturally. If it sits on concrete or you want to prevent weeds from growing up through the bottom, landscape fabric works well. Avoid plastic, which traps water and rots roots. Cardboard is cheaper and biodegrades over time.

How deep should a raised bed be?

Most vegetables and flowers do well in 12 inches of soil. Root vegetables like carrots and parsnips need 12 to 18 inches. Shallow-rooted plants like lettuce and herbs can grow in 8 inches. Deeper beds hold more water and give roots more room, but they also require more soil and cost more to fill.

Can I reuse soil from last year?

Yes, but refresh it first. Remove the top 2 to 3 inches (which may contain disease spores or pest eggs), then mix the remaining soil with fresh compost at a 2-to-1 ratio. This restores nutrients and structure without the cost of replacing all the soil. Do this every two to three years to keep the bed healthy.

What's the difference between topsoil and garden soil?

Topsoil is mostly soil with little added organic matter. Garden soil is topsoil mixed with compost, peat moss, or other amendments to improve drainage and nutrition. Garden soil is better for raised beds because it holds nutrients longer, but it costs more. A blend of both works well and splits the difference in price.

Should I add perlite or sand to my soil mix?

Add perlite or coarse sand only if your soil is heavy clay or drains poorly. Most commercial topsoil and garden soil mixes already have enough drainage material. Adding too much perlite or sand makes the soil drain so fast that it dries out quickly and doesn't hold nutrients well.