Growing vegetables, flowers, and herbs in a raised garden bed is a handy solution if you have poor soil or drainage problems, and it allows you to start planting earlier in spring. But how deep should a raised garden bed be to gain the most benefit for your plants? In this guide, we’ll help you determine the best depth for your raised beds and how much soil you need to fill them. You’ll also find useful tips to ensure your raised garden is a success.

Best Raised Garden Bed Depth

How deep you need to make your raised beds depends on your gardening goals, the plants you would like to grow, the quality of your existing soil, your budget, and the location of your garden. But in general, 12 inches tall is a suitable depth for most common veggies and herbs. However, plants with deep root systems require deeper beds, while shallow-rooted plants do fine in as little as 6 inches of soil.

Aside from plant root depth, it is also important to consider your budget and how you want to use your garden. Taller raised beds are typically more expensive than shorter ones, but they tend to be more ergonomic and easier on your back. Shorter beds are usually more budget-friendly because they require less soil, but they dry out faster and require more frequent watering than taller raised beds.

Recommended Soil Depth for Common Plants

While aesthetics and your budget will undoubtedly play a role in your raised bed design, the most important factor to consider when building a raised bed is the root systems of the plants you’d like to grow. Some plants need a lot more soil space than others, and planting crops in soil that’s too shallow causes stunted growth and increases the chances that your plants will topple over in windy weather.

To avoid these issues, here’s a basic rundown of the minimal soil depth required for the most common edible and ornamental plants:

• Most herbs, lettuce, and other plants with shallow root systems grow in beds that are at least 6 inches deep.
• Root veggies, celery, peppers, brassicas, alliums, potatoes, strawberries, and legumes (beans and peas) need at least 12 inches of soil to grow properly.
• Tomatoes, eggplants, and cucurbits such as squash and melons, have deeper root systems and are best grown in beds that are at least 18 inches deep.
• Crops like corn, rhubarb, and artichokes have even deeper roots and they’re generally not recommended for raised-bed gardening.
• The soil depth required for perennial and annual flowers varies significantly from plant to plant. Most flowers can be grown in 12- to 18-inch-deep beds.

How Much Soil Will You Need?

Raised beds are typically filled up with raised bed soil mix or a DIY soil blend made with 1 part topsoil and 1 part compost or other organic matter. Soil mixes are available in bags or bulk from landscaping and garden centers.

To calculate exactly how much soil you need for each raised bed, measure the total length, width, and height of your raised beds. Multiply these three numbers. For instance, if your raised bed is 4 feet wide, 8 feet long, and 1 foot deep, you need about 32 cubic feet of soil (4 x 8 x 1 = 32).

Tips for Creating DIY Raised Beds

Deciding how deep raised beds should be is just one part of building a raised bed garden. To ensure your raised beds are perfect for your plants, here are a few more tips to keep in mind:

• Low-cost soil alternatives. Instead of using only soil to fill your raised beds, save money by filling the base of raised beds with organic matter, such as autumn leaves, that will eventually decompose into the soil. This will reduce the amount of soil you’ll have to purchase.
• Budget-friendly DIY raised beds. Commercially made raised bed frames are typically made from wood or galvanized steel. A more budget-friendly option is building your own raised bed from scratch, for example with untreated, pine ledger board.
• Maximum raised bed length. In theory, raised beds can be as long as you like them to be, but keeping them under 4 feet wide will make them easier to access for planting, weeding, watering, and harvesting.
• Keeping pests out. If your garden is plagued by burrowing rodents such as voles, install hardware cloth on the base of each raised bed before filling the beds with soil.
• Stabilizing the raised beds. Raised beds that are more than 6 feet long or 1 foot deep are more likely to bow out at the sides when filled with soil. Prevent this by adding braces for support across the middle of each bed or installing several short, sturdy stakes along the bed’s length.
• Maximize sun exposure. To take advantage of the sun, orient raised beds in a north-to-south direction. Plant taller crops on the north side of the bed so they won’t overshadow shorter plants.