To fill an 8×4 raised bed, you will need about 4-6 cubic yards of soil, or 128-192 cubic feet. The exact amount depends on how deep you want to fill the bed.
Calculating Soil Volume for a Raised Bed
To figure out how much soil you need, you’ll first need to calculate the volume of the raised bed. Here’s the simple formula:
Length x Width x Depth = Volume in cubic feet
So for an 8×4 raised bed, it would be:
8 x 4 x 1 = 32 cubic feet (at 1 foot deep)
Some key details about calculating raised bed soil volume:
- Measure length, width and depth in feet for cubic feet
- Depth is how deep you want to fill the bed with soil, often 6-12 inches
- 1 cubic yard is equal to 27 cubic feet
Sample Volumes for an 8×4 Raised Bed
|Depth||Volume (cubic feet)||Volume (cubic yards)|
As you can see, the volume ranges from 64 cubic feet (at 6 inches deep) to 128 cubic feet (at 12 inches deep). That converts to 2.4 to 4.7 cubic yards of soil.
In most cases, you’ll want to fill the bed 8-12 inches deep, which would mean getting 3-5 cubic yards of soil.
What Type of Soil is Best?
When choosing soil for a raised bed, look for a high-quality garden soil or potting mix. Avoid heavy clay soils, which can become compacted. Recommended options:
- Organic raised bed soil mix – contains compost, peat moss, perlite and vermiculite.
- Potting soil or potting mix – light, fluffy and good drainage.
- Topsoil blended with compost – improves drainage and nutrients.
- Container garden soil – specially blended for optimal growth.
A soil depth of 8-12 inches provides good root growth for most vegetables and flowers. Make sure the soil is loose and not compacted.
Where to Buy Raised Bed Soil
You can purchase bagged soil, bulk soil, or have bulk soil delivered for raised garden beds:
- Bagged soil – Sold at home improvement and garden stores. Get organic mixes sold specifically for raised beds.
- Bulk soil – Some stores sell soil by the cubic yard that you shovel yourself. Loading bulk soil into a truck bed can be messy.
- Bulk delivery – Order soil by the cubic yard from landscape companies or nurseries. Have it delivered right to your driveway or yard. More expensive but very convenient.
When estimating how many bags you need, remember that 1 cubic foot equals about 8, 5-gallon bags of potting soil.
For a 4×8 raised bed filled 8 inches deep, you would need about 35 bags total. Buying bagged soil can get expensive for larger beds.
Filling the Raised Bed with Soil
Filling a deep raised bed with multiple yards of soil materials can be challenging. Here are some tips:
- Have bulk soil dumped directly into the bed from a truck delivery. Shovel and rake it evenly.
- Use a wheelbarrow to dump bagged soil into the raised bed.
- Place boards across the bed when partially full to walk on it without compressing the soil.
- Add compost, fertilizer, or other amendments after filling and mix in well.
Take your time when filling, and don’t overload wheelbarrows to avoid back strain. Enlist some help from friends to make light work of this soil filling raised bed project.
Costs of Raised Bed Soil
So how much will it cost to fill your raised bed? Here are some rough estimates:
- Bagged potting soil or raised bed mix: $10 – $15 per cubic foot
- Bulk garden soil: $25 – $45 per cubic yard
- Bulk soil delivery: $35 – $75 per cubic yard
For a 4×8 foot bed filled 10 inches deep (requiring 4 cubic yards), the total cost would be:
- 128 bags potting mix: $1,280 ($10/bag)
- 4 yards bulk soil: $160 ($40/yard)
- 4 yards delivered: $260 ($65/yard delivery)
As you can see, bulk soil delivery is the cheapest option for large raised beds. Potting mix bags get very pricey in bulk quantities.
Tips for Choosing Raised Bed Soil
Follow these tips when selecting and buying soil for your raised bed garden:
- Check soil pH – aim for a neutral 6.5-7.0 pH for most vegetables.
- Get soil tested – tests reveal nutrient levels to identify amendments needed.
- Avoid heavy clay – pick light, loamy mixes that resist compaction.
- Use sterile soil – reduces risk of introducing diseases and pests.
- Read labels – select mixes formulated specifically for raised beds.
- Ask an expert – consult with knowledgeable nursery staff for advice.
- Buy early – soil can sell out quickly in spring rush. Plan ahead.
With quality soil matched to your raised bed size, you’ll give your plants the right foundation to thrive. It’s worth the effort and modest expense to fill your raised beds properly.
Alternative Options for Filling Raised Beds
Purchasing large amounts of topsoil or potting mixes can get expensive. Here are some alternate options for filling raised garden beds on the cheap:
Use Native Soil
If your native soil is decent quality, simply use that rather than trucking in new material. Test soil and amend as needed with compost.
Make Your Own Soil Mix
DIY soilless mixes with peat moss, coconut coir, perlite and vermiculite can be cheaper than bagged potting soil. Takes more work to mix and prepare.
Try Lasagna Gardening
Layer newspaper, compost, manure and other organic materials in sheets. Allows you to build up soil over time.
Fill Partially with Compost
Use cheaper bulk compost for the bottom half of the bed, then top with quality soil mix. Saves money over all new soil.
Recycle Old Soil
Recondition used raised bed soil by mixing in new compost. Can reuse a few seasons before replacing.
While these options do involve more labor, creativity and planning, they can stretch your dollar further on large raised bed projects.
Frequently Asked Questions
How deep should soil be in a raised bed?
Aim for a soil depth of 8-12 inches in a raised bed. This provides plenty of root space for most vegetable plants. Shallow beds less than 6 inches deep restrict growth.
Can I use bagged soil from the store?
Yes, you can use standard bagged topsoil or potting mix. But higher quality options specifically blended for raised beds will give you better results.
When should I fill my raised bed?
It’s best to fill raised beds 2-3 weeks before planting, allowing the soil to settle. Don’t plant immediately after filling.
Do I need to replace raised bed soil each year?
No, you don’t need to replace the soil annually. Top off beds by mixing in 1-2 inches of compost each spring. Every 2-4 years, replacing all the soil is recommended.
Can I use compost alone to fill a raised bed?
It’s not recommended to use 100% compost, as it can compact over time. Mix compost with potting soil, topsoil or a prepared raised bed blend instead.
Determining soil needs for a raised bed involves some simple volume calculations and consideration of soil quality and filling options. With a properly filled raised bed of about 4-6 cubic yards of soil for an 8×4 foot bed, you’ll give your plants the right foundation to thrive. Filling your new raised bed properly is worth the effort and investment for many seasons of bountiful harvesting to come.