Raised Bed Soil Guide
Create the perfect growing medium for your raised garden beds
Quick Reference
Why Raised Bed Soil Matters
Raised beds give you complete control over your growing medium. Unlike in-ground gardens where you're stuck with native soil, you can create the perfect blend for vegetables. Good raised bed soil should:
- Drain well while retaining adequate moisture
- Stay loose and friable so roots can spread easily
- Provide steady nutrients throughout the season
- Support beneficial soil organisms
The Classic 60-30-10 Mix
This tried-and-true recipe works for most vegetables and is easy to source locally.
Topsoil
Provides body and minerals. Use screened topsoil from a landscape supplier, not the cheap "fill dirt." Should be dark brown and crumbly, not gray or chunky.
Compost
Adds nutrients and organic matter. Mix different types for best results: mushroom compost, leaf compost, and composted manure. Should smell earthy, not sour.
Aeration
Prevents compaction. Use perlite, coarse sand, or small pine bark. This keeps soil loose and well-drained for years. Skip if using very coarse compost.
Alternative Soil Recipes
Mel's Mix (Square Foot Gardening)Popular
Equal parts peat moss (or coco coir), vermiculite, and blended compost. Very light and fluffy - great for intensive planting. More expensive but requires no soil at all.
Budget Mix
50% topsoil, 50% compost. Simpler and cheaper than the 60-30-10, but may compact more over time. Add a few inches of mulch on top to keep soil loose.
Lasagna/Hugelkultur Base
Fill the bottom third with logs, branches, and coarse organic matter. Top with cardboard, then layers of compost, leaves, and soil. Takes longer to mature but creates amazing soil.
Calculating How Much Soil You Need
Use this formula to calculate cubic feet of soil needed:
Common bed sizes:
- • 4x4 bed, 8" deep = 10.6 cu ft
- • 4x8 bed, 8" deep = 21.3 cu ft
- • 4x8 bed, 12" deep = 32 cu ft
- • 4x12 bed, 12" deep = 48 cu ft
Bulk ordering:
- • 1 cubic yard = 27 cubic feet
- • Bulk delivery is cheapest for 3+ yards
- • Order 10% extra to account for settling
- • Most trucks can carry up to 15 yards
Sourcing Your Materials
Bulk Landscape Suppliers
- • Best price for large quantities
- • Can mix soil blends on-site
- • Often offer delivery
- • Ask about "garden blend" or "raised bed mix"
Bagged Products
- • Convenient for small beds
- • Consistent quality and sterile
- • More expensive per cubic foot
- • Check for "raised bed" specific mixes
Mistakes to Avoid
- • Using only compost - Too rich, holds too much water, and breaks down quickly
- • Cheap "garden soil" bags - Often poor quality with debris and weed seeds
- • No drainage layer - Don't put gravel at the bottom; it actually impedes drainage
- • Soil from unknown sources - May contain herbicides, heavy metals, or diseases
- • Filling to the very top - Leave 1-2 inches for mulch and water catchment
Maintaining Raised Bed Soil
Yearly Tasks
Add 1-2 inches of compost each spring. Soil level drops as organic matter decomposes - this is normal. Top-dress rather than tilling to protect soil structure and organisms.
Cover Crops
Plant cover crops in fall to add organic matter and prevent soil erosion. Winter rye, crimson clover, and field peas are excellent choices that you can cut down in spring.
Long-term Refresh
Every 3-5 years, consider adding fresh soil mix if beds have compacted significantly. Test soil pH and nutrients to catch any imbalances before they cause problems.
Frequently Asked Questions
What is the best soil mix for raised beds?
The classic raised bed mix is 60% topsoil, 30% compost, and 10% aeration material (perlite or coarse sand). This provides nutrients, drainage, and structure. Some gardeners prefer the simpler 'Mel's Mix': equal parts compost, peat moss, and vermiculite.
How deep should soil be in a raised bed?
Most vegetables need at least 6-8 inches of soil depth. For root crops like carrots or potatoes, aim for 12 inches. If your raised bed sits on concrete or compacted soil, you'll need the full depth; if it's on good garden soil, roots can extend below.
Can I use garden soil in raised beds?
Pure garden soil can compact in raised beds, reducing drainage. Mix it 50/50 with compost, or use it as 60% of a soil-compost-amendment blend. Never use soil from areas treated with herbicides or near roads.
How much soil do I need for a raised bed?
Calculate cubic feet: length x width x depth (in feet). A 4x8 foot bed that's 1 foot deep needs 32 cubic feet. One cubic yard equals 27 cubic feet. Most bagged soil is sold in cubic feet - check the label to calculate how many bags you need.