How Much Soil Do I Need?
Calculate the amount of soil you need for your raised bed or planter garden
Good soil is the single most important ingredient for a good garden. Raised beds give you an immediate advantage over an in-ground garden, because you can fill your raised bed with a blend of soil that's superior to the native soil (or sometimes, unfortunately, dirt) in your yard. Soil that's loose and rich with nutrients and organic matter will allow the roots of your plants to grow freely, and ensure that they have access to the water and nutrients they need to sustain healthy growth.
Example: How Much Soil Do I Need for a 3x6 Bed?
To fill a 3x6 bed with 10" sides, you will need 15 cubic feet of blended soil. To create the blend, use the following quantities:
- 9 cubic feet of topsoil (9 20-quart bags)
- 4.5 cubic feet of compost (4.5 20-quart bags)
- 1.5 cubic feet of soilless potting mix
- 1.5 cups fertilizer
Before placing your raised garden beds in their permanent location, be sure to remove any grass or perennial weeds from the area. Use a garden fork or shovel to loosen the native soil to a depth of 6-10″. This will improve drainage and moisture retention in the raised beds. It also means that even with a 5″-high raised bed, your plants will think they're growing in a bed that's 12-18″ deep — plenty of room for carrots, potatoes, full-size tomato plants and most any other vegetable you'd ever want to grow.
'Soil Recipe': Creating an Ideal Soil Blend for Raised Bed Gardens
If you'll be filling more than one raised bed, you may want to buy your soil in bulk — by the cubic foot or cubic yard. Use the Soil Calculator to figure out the total amount of soil you'll need for each bed. For most situations, we recommend these proportions:
- 60 percent topsoil
- 30 percent compost
- 10 percent soilless growing mix - also known as potting mix.
Keep in mind that proportions are approximate because soil volume varies from source to source. For instance, if the calculator specifies 0.444 cubic yards of soil for your bed, go ahead and round it up to a half yard.
If you do not have access to quality topsoil, an acceptable substitute would be a 50-50 blend of soilless growing medium and compost. If you want to add peat moss to the bed, it should not be more than 20 percent of the total mix. Peat moss is naturally acidic and is not a good medium for growing vegetables.
