Fill a raised bed in layers, starting with coarse material at the bottom for drainage, then adding soil amendments, and finishing with topsoil

The fastest way to fill a raised bed is to use the lasagna method: lay cardboard or newspaper on the ground beneath the bed to block weeds, then add a 2- to 4-inch layer of coarse material (wood chips, straw, or leaves), a 2- to 3-inch layer of compost or aged manure, and finish with 6 to 8 inches of topsoil or garden soil. This approach costs less than buying all topsoil, drains better than soil alone, and settles over time as the lower layers decompose.

If you are filling a bed that sits directly on soil with no barrier, skip the cardboard step — water will drain through the bottom naturally. If the bed sits on concrete or compacted ground, the cardboard layer prevents water from pooling underneath.

Key Takeaways

  • Layering coarse material, compost, and topsoil costs less and drains better than filling entirely with topsoil.
  • A raised bed 12 inches deep typically needs 8 to 10 cubic feet of material, which you can calculate by multiplying length × width × depth in feet, then dividing by 27 to convert to cubic yards.
  • Wood chips and leaves break down over time, so expect the bed to settle 1 to 2 inches in the first year and plan to top it off with fresh soil.
  • Cardboard or newspaper under the bed blocks weeds only if the bed sits on soil; it is unnecessary on concrete or if you do not mind weeds coming up from below.

Calculate how much material you need before you buy

Measure the inside length and width of your bed in feet, then measure the depth you want to fill. Multiply length × width × depth to get cubic feet. Divide that number by 27 to convert to cubic yards — the unit most soil suppliers use.

A 4-foot by 8-foot bed filled 12 inches deep needs 12 cubic feet, or about 0.4 cubic yards. A 4-foot by 4-foot bed at the same depth needs 4 cubic feet, or about 0.15 cubic yards. Suppliers often sell in half-cubic-yard or full-cubic-yard increments, so you may need to round up or buy a little extra.

If you are using the layering method, you do not need to buy all topsoil. A 12-inch-deep bed can be filled with 4 inches of coarse material, 3 inches of compost, and 5 inches of topsoil. This mix usually costs 30 to 40 percent less than filling the entire bed with topsoil alone.

Choose materials for the bottom layer

Wood chips are the most common choice for the bottom layer. They drain well, break down slowly (taking 2 to 3 years), and cost little if you can source them free from tree services. Avoid treated wood chips, which may contain copper or arsenic. Fresh wood chips can temporarily tie up nitrogen as they decompose, but this effect is minor in a layered bed where compost sits above.

Straw (not hay, which contains seeds) works well and breaks down faster than wood chips — usually within one season. Shredded leaves are free if you have trees and break down quickly, adding organic matter. Cardboard can form the very bottom layer to block weeds, but it is not a substitute for the coarse material layer; use it underneath, not instead of wood chips or straw.

Do not use sawdust alone, as it compacts and sheds water. Avoid glossy cardboard or cardboard with tape, staples, or plastic coating.

Add compost or aged manure in the middle

Finished compost — dark, crumbly, and without a strong smell — adds nutrients and improves water retention. Aged manure (at least 6 months old) does the same. Fresh manure can burn plant roots and should not go directly in a bed you plan to plant in right away. If you use fresh manure, let the bed sit for 4 to 6 weeks before planting.

Aim for 2 to 3 inches of compost or aged manure in the middle layer. This is where most of the nutrients live, so do not skip it even if it costs more than wood chips. Bagged compost is convenient but expensive for large beds; bulk compost from a landscape supplier is cheaper per cubic yard.

Top with garden soil or topsoil

The top 6 to 8 inches should be topsoil or garden soil — the material plants actually root into. Topsoil is screened and relatively free of rocks and debris. Garden soil is topsoil mixed with compost and is richer but costs more. For most vegetables and flowers, either works.

Do not use potting soil, which is designed for containers and is too expensive for a large bed. Do not use subsoil (the pale, compacted layer below topsoil), which drains poorly and lacks nutrients.

Fill to within 1 to 2 inches of the rim so water does not spill over the edge when you water. The bed will settle over the first few weeks; you can top it off with an extra inch or two of topsoil or compost once it has settled.

Account for settling and plan to refresh the bed each year

The coarse material at the bottom breaks down and compacts, so a bed filled 12 inches deep will settle to 10 or 11 inches within the first year. This is normal. In subsequent years, add 1 to 2 inches of fresh compost or topsoil each spring to bring the level back up and replenish nutrients.

After 3 to 5 years, the original coarse material will have mostly decomposed. At that point, you can either add another layer of wood chips or compost to the bottom and refill, or straightforward top the bed with fresh soil and compost each year. Many gardeners find it easier to just keep adding to the top rather than emptying and refilling.

Avoid common mistakes when filling

Do not fill the bed all at once if it is very tall or if you are using heavy material like clay soil — the weight can shift the frame or cause uneven settling. Fill in stages if the bed is deeper than 18 inches, letting each layer settle before adding the next.

Do not pack the soil down hard. Let it settle naturally under its own weight and the first few waterings. Compacting it reduces drainage and makes it harder for roots to penetrate.

Do not use soil from your yard if it is heavy clay or compacted. Raised beds work best with loose, well-draining soil. If you must use yard soil, mix it 50/50 with compost or topsoil.

Frequently Asked Questions

Can I fill a raised bed with just topsoil?

Yes, but it costs more and may not drain as well. Topsoil alone can compact over time, especially if it is clay-heavy. Layering with coarse material underneath improves drainage and costs less.

How long does it take for a raised bed to settle?

Most settling happens in the first 2 to 4 weeks as the soil compacts under its own weight and the first waterings. Coarse material at the bottom continues to break down over months and years, causing gradual settling. Expect 1 to 2 inches of total settling in the first year.

Can I use leaves from my yard instead of buying mulch?

Yes. Shredded leaves work well as a bottom layer and are free. Whole leaves mat together and shed water, so shred them first with a mower or leaf shredder. Leaves break down faster than wood chips, usually within one season.

What if I fill the bed and then realize I used the wrong soil?

You can remove the top layer and replace it, or mix in compost to improve drainage and structure. If the soil is too heavy, adding 2 to 3 inches of compost and mixing it in will help. You do not have to empty the entire bed.

Should I add fertilizer when I fill the bed?

No, not usually. Compost and aged manure provide enough nutrients for the first season. You can add a balanced fertilizer (like 10-10-10) once plants are growing if they show signs of nutrient deficiency, but most new beds do not need it right away.