There are many reasons to create raised beds in the landscape or garden. Raised beds can be an easy remedy for poor soil conditions, such as rocky, chalky, clay, or compacted soil. They are also a solution for limited garden space or adding height and texture to flat yards.
Raised beds can help deter pests like rabbits. They can allow gardeners with physical handicaps or limitations easy access to their beds as well.
How much soil goes in a raised bed depends on the bed height, and what will be grown. Continue reading for more information on raised bed soil depth.
About Soil Depth for Raised Beds
Raised beds can be framed or unframed. Unframed raised beds are often called berms andare simply garden beds made of mounded up soil. These are most commonly created for ornamental landscape beds, not fruit or vegetable gardens.
Unframed raised bed soil depth depends on what plants will be grown, what the soil conditions under the berm are, and what the desired aesthetic effect is.
Trees, shrubs, ornamental grasses, and perennials can have root depths anywhere between 6 inches (15 cm.) to 15 feet (5 m.) or more.
Tilling the soil beneath any raised bed will loosen it up so that plant roots can reach the depths that they need for proper nutrient and water uptake.
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In locations where the soil is of such poor quality that it cannot be tilled or loosened, raised beds or berms will need to be created higher, resulting in more soil needing to be brought in.
How Deep to Fill a Raised Bed
Framed raised beds are frequently used for vegetable gardening. The most common depth of raised beds is 11 inches (28 cm.) because this is the height of two 2x6 inch boards, which is commonly used to frame raised beds. Soil and compost are then filled into the raised beds to a depth just a few inches (8 cm.) below its rim.
A few flaws with this are that while many vegetable plants need a depth of 12 to 24 inches (31-61 cm.) for good root development, rabbits can still get into beds that are less than 2 feet (61 cm.) high, and a garden 11 inches (28 cm.) high still requires a lot of bending, kneeling, and squatting for the gardener.
If the soil beneath a raised bed is not suitable for plant roots, the bed should be created high enough to accommodate the plants. The following plants can have 12 to 18 inch (31-46 cm.) roots:
Root depth from 18 to 24 inches (46-61 cm.) should be expected for:
Then there are those having much deeper root systems of 24 to 36 inches (61-91 cm.). These may include:
Decide on the type of soil for your raised bed. Bulk soil is most often sold by the yard. To calculate how many yards are needed to fill a raised bed, measure the length, width, and depth of the bed in feet (you can convert inches to feet by dividing them by 12).
Multiply the length x width x depth. Then divide this number by 27, which is how many cubic feet are in a yard of soil. The answer is how many yards of soil you will need.
Keep in mind that you will most likely want to mix in compost or other organic matter with regular topsoil. Also, fill raised garden beds to a few inches (8 cm.) below the rim to leave room for mulch or straw.
FAQs
Multiply the length x width x depth. Then divide this number by 27, which is how many cubic feet are in a yard of soil. The answer is how many yards of soil you will need.
How deep should soil be in a raised bed? ›
They should have at least 8 inches of soil depth to accommodate the root systems of plants, because the majority of plant roots require 6 – 8 inches of soil for healthy root growth. A depth of 8 – 12 inches will suffice for most gardening situations.
How do I calculate how much soil I need for a raised bed? ›
To calculate:
- Measure the length, width and height of your bed. (Unless the boards are very thick, don't worry about inside/outside measurements.) ...
- Multiply all the measurements together: 6 x 3 x 1.4 = 25.2 cubic feet.
- Divide the answer by 27 to get the number of cubic yards.
Filling the Raised Garden Beds
For beds six to 12 inches deep, fill completely with soil. For deeper beds, it's sometimes helpful to add other materials to take up space and reduce the overall amount of soil, but it depends on your preference and soil availability.
How much soil depth do vegetables need to grow? ›
A 1-foot raised bed is more than enough to accommodate a salad garden box plan. Carrots, radishes and peppers thrive with 12 inches or more. Medium-rooting vegetables like kale, cucumbers, and zucchini love at least 18 inches.
How deep does a raised garden bed need to be for tomatoes? ›
Tomatoes should ideally be grown in a raised bed that's at least 15 to 18 inches deep. Many of my clients in Houston are successfully growing tomatoes in 12-inch deep raised garden beds, but their plants tend to be a little stunted compared to plants in deeper beds.
How deep does a raised bed need to be for potatoes? ›
Fingerling potatoes are small, prolific, and tasty, and are therefore especially appropriate for raised beds. Setting up Raised Beds: Raised beds should be at least 12 inches deep and filled to about six inches with a good planter mix and lots of compost.
What is the best soil mixture for raised beds? ›
Add a mixture of compost and purchased topsoil in a 1:2 or 1:1 ratio, to the top of the bed. There are vendors who sell topsoil mixed with compost. Alternatively, fill the bed with compost and a soilless growing mix in a 1:1 ratio.
How deep should topsoil be? ›
Lawns: The recommended depth of topsoil for creating lawns from turf or seed is 4 to 6 inches. General: 6 to 9 inches of soil is usually sufficient for most planting. Vegetables: The depth of topsoil for growing vegetables will vary depending on what you plan to grow.
How many inches of soil do I need? ›
To estimate soil volume for any area, all you need is a tape measure. “The basic formula is simple: Length x Width x Height = Volume,” says Michael Dean, co-founder of Pool Research. Then divide the number of cubic feet by 27. So one cubic yard = 27 cubic feet = 1,728 cubic inches.
Seven Beginner Raised Bed Gardening Mistakes to Avoid
- Picking The Wrong Spot. It is a common gardening mistake made by many gardeners. ...
- Not Thinking About The Water Source. ...
- Raised Beds Placed Too Close Together. ...
- Crowding your Plants. ...
- Planting the Wrong Plants. ...
- Skipping Mulch. ...
- Not Using the Correct Soil.
Raised beds that are small and shallow (under 12 inches deep) are typically only filled with soil. Adding other organic materials to shallow beds usually isn't a good idea. Sticks, twigs, and other materials further reduce the limited soil space and can interfere with plant root growth and water drainage.
How deep should soil be for raised beds? ›
The most popular height for raised beds is 11″. (This is the height of two standard “2 x 6″ boards, which actually measure 1.5″ x 5.5”.) This height provides sufficient drainage for most crops. For best results, there should be another 12″ or more of good soil below the bed.
What vegetables don't need deep soil? ›
Effective Root Zone (in inches) for Shallow Rooted Vegetables
| Vegetable/Crop | Effective Root Zone Depth (in inches) |
|---|
| Radish | 6 (16 cm) |
| Shallots | 12 (31 cm) |
| Spinach | 6 (16 cm) |
| Swiss Chard | 12 (31 cm) |
9 more rowsOct 6, 2023
Plant Tomatoes Deep, Deep, Deep. Each Bonnie tomato label urges you to plant tomatoes deep, so that a full 2/3 of the plant is underground. That means that if you buy a 10-inch tall plant, all but the top three to four inches is buried.
What do you put in the bottom of a raised garden bed? ›
Layer the bottom with cardboard or newspaper as a weed barrier, which will decompose over time. Then, use a mix of yard waste, leaves, grass clippings, and kitchen scraps layered with soil and compost.
How deep does soil need to be for tomato plants? ›
Choose healthy plants that are 10 to 12 inches tall. Dig your hole about 12 inches deep for each plant and work a handful of good fertilizer into the hole. (Heyming also likes to add a banana peel and the shells from one egg into the bottom of the hole to provide extra nutrients for the roots later in the season.)
What vegetables can grow in 8 inches of soil? ›
Shallow-rooted vegetables root to a depth of 6 to 12 inches, making them ideal for container gardening or gardens with limited soil depth. Some of the best shallow-rooted vegetables include: Swiss Chard, Chives, Endive, Celery, Lettuce, Onions (bunch), Onions (dry), Spinach, Fennel, Shallot, and Radish.
What can grow in 6 inches of soil? ›
While many plants need at least 12 inches of soil to grow well, others, like lettuce and annual flowers like pansies, sweet alyssum, and dwarf marigolds, can thrive in as little as 6 inches.
