Calculate how much soil you need before you buy
The amount of soil depends on the length, width, and depth of your raised bed. Measure all three dimensions in feet, then multiply them together to get cubic feet. A raised bed that is 4 feet long, 2 feet wide, and 12 inches deep needs 8 cubic feet of soil (4 × 2 × 1 = 8).
Most soil is sold by the cubic yard, not cubic feet. One cubic yard equals 27 cubic feet. If your bed needs 8 cubic feet, you would need roughly one-third of a cubic yard. Garden centers often sell smaller bags (typically 1 to 2 cubic feet per bag) if you prefer to avoid ordering a full yard delivered.
Add 10 to 15 percent extra to your calculation to account for settling. Soil compacts over time, especially in the first few weeks, so the bed will sink slightly after you fill it.
Key Takeaways
- Multiply your bed's length, width, and depth in feet to find how many cubic feet of soil you need.
- A layered approach—compost on the bottom, topsoil in the middle, and finished compost on top—creates better drainage and plant nutrition than a single soil type.
- Dampen the soil as you add it so it settles evenly and compacts properly.
- Plan to add more soil after the first month because new beds settle noticeably.
Choose a soil mix that drains well and holds nutrients
Do not use only garden soil from your yard or bagged garden soil alone. Garden soil is dense and compacts easily, which blocks water and air from reaching roots. Instead, mix three types of material: compost, topsoil, and peat moss or coconut coir.
A common formula is one-third compost, one-third topsoil, and one-third peat moss or coconut coir. This blend drains well, holds moisture without waterlogging, and provides nutrients for the first season. Compost breaks down over time and feeds plants; topsoil provides structure; and peat or coir keeps the mix light and airy.
If you prefer to buy a pre-mixed product, look for raised bed soil or garden mix at garden centers. These are formulated to drain quickly and are lighter than straight topsoil. Read the label to confirm it contains compost and does not rely on garden soil as the main ingredient.
Layer the materials for better results
Layering creates natural separation and improves drainage. Start with a 3- to 4-inch layer of coarse material at the bottom—shredded leaves, straw, or wood chips work well. This layer allows water to drain away from plant roots and breaks down slowly to add organic matter.
Add a 4- to 6-inch layer of topsoil next. This is the structural base that holds nutrients and supports root growth. Then add a 3- to 4-inch layer of finished compost on top. Finished compost is dark, crumbly, and fully decomposed; it provides when ready nutrients and improves water retention.
If your bed is deeper than 12 inches, you can repeat this pattern. The goal is to avoid a solid block of one material that compacts and blocks drainage.
Fill the bed in stages and water as you go
Do not dump all the soil at once and then water it. Instead, add soil in 4- to 6-inch layers and dampen each layer lightly with a hose or watering can. This helps the soil settle evenly and prevents air pockets that can cause uneven settling later.
Water each layer until it is moist but not soggy—you should be able to squeeze a handful and have it hold together without dripping. This moisture helps the soil compact naturally and makes it easier to work with as you add the next layer.
Stop filling when the soil reaches about 1 to 2 inches below the top edge of the bed. This leaves room for mulch and prevents soil from washing over the sides when you water.
Plan to add more soil after the first month
New raised beds settle noticeably in the first few weeks. The soil compacts under its own weight, and organic materials like compost and leaves begin to break down. You may see the soil level drop by 2 to 4 inches.
After about four weeks, add a fresh layer of compost or topsoil to bring the bed back to its original level. This is normal and expected—do not assume you miscalculated. Settling continues at a slower rate after the first month, so you may need to top it off once or twice more during the first season.
Avoid common mistakes that waste money or create problems
Do not use only compost. Pure compost is too rich and breaks down too quickly, leaving you with a sunken, nutrient-poor bed by mid-season. It also drains poorly when packed tightly. Always mix it with topsoil and a light, airy material.
Do not use garden soil as your main ingredient. It is heavy, compacts easily, and often contains weed seeds and clay that block drainage. If you have good garden soil from your yard, mix it in at no more than one-third of the total volume.
Do not skip the bottom layer. A coarse base layer prevents the soil from becoming waterlogged and gives roots room to grow downward. Without it, water pools at the bottom and can rot roots or encourage fungal problems.
Do not fill the bed completely to the top. Leaving 1 to 2 inches of headroom prevents soil from spilling over during watering and gives you space to add mulch, which keeps weeds down and retains moisture.
Know when to call a landscaper or soil delivery service
If your raised bed is very large or you are filling multiple beds, ordering soil delivery is faster and cheaper than buying bags. Most landscape supply companies deliver bulk soil for a flat fee plus the cost of the soil. Get quotes from at least two suppliers—prices vary widely by region.
If you have a bad back or mobility issues, a delivery service is worth the cost. Bags of soil are heavy (typically 40 to 50 pounds each), and filling a large bed by hand can take hours.
If you are unsure whether your soil mix is right for your plants, ask the garden center staff or a local extension office. They can recommend a mix based on what you plan to grow.
Frequently Asked Questions
Can I use only compost to fill a raised bed?
No. Pure compost breaks down quickly, leaving you with a sunken bed by mid-season, and it drains poorly when packed. Mix compost with topsoil and a light material like peat moss or coconut coir for better results.
How deep should a raised bed be?
Most vegetables need 10 to 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 6 to 8 inches. Deeper beds give roots more room and reduce watering frequency.
What is the difference between topsoil and garden soil?
Topsoil is the upper layer of natural soil, screened and sold for landscaping. Garden soil is topsoil mixed with compost and other amendments to improve drainage and nutrition. For raised beds, garden soil is usually better than plain topsoil, but mixing your own blend gives you more control.
Should I line the bottom of my raised bed before filling it?
Lining is optional. A cardboard or landscape fabric layer at the bottom slows weed growth from below and can prevent soil from mixing with contaminated ground. If your yard has clay soil or poor drainage, a layer helps. If drainage is already good, lining is not necessary.
How often do I need to refill my raised bed with soil?
Add compost or topsoil once a year, usually in spring. Organic materials break down over time, so the bed sinks gradually. Adding 1 to 2 inches of compost each year keeps the soil level stable and replenishes nutrients.