Setting up a raised garden bed in your garden is a good idea if you want to grow your own produce. It can lengthen your growing season because it warms up faster and drains better than soil in the ground.
If you’re worried that having a raised garden bed is difficult to achieve because it has to be very deep to be effective, that isn’t the case.
Generally, your raised garden bed should be around 12 inches deep. However, if you’re growing vegetables, your garden bed usually needs to be between 12 and 18 inches deep to accommodate their roots.
This article will explore the ideal depth of your raised bed according to the different plants you want to grow. We’ll also look at why it’s important to avoid making your raised garden bed too deep or too shallow.
Ideal Depth of Raised Garden Bed According to Plant Type
It’s a misconception to think that you can make your raised garden bed very deep and plant a variety of produce in it.
The optimal depth for your raised garden bed depends on what you’re planting in it. If you’re growing different produce in the same bed, you’ll have to ensure they have similar depth requirements, otherwise, you’ll run into problems.
Here’s a rundown of what depth you’ll need based on different types of plants and produce.
If you’re growing produce with shallow roots, such as herbs, you only need about six inches of depth in your raised garden bed. This is why herbs are such a fantastic type of produce to grow. You can grow them in a variety of small spaces, without requiring many resources.
However, the exception to this six-inch rule is if you’re planting rosemary in a raised garden bed. You’ll need to provide it with 12 inches of space for its roots because it has a larger root system.
Plants with Shallow Roots—12–18 inches
If you’re growing produce that has deeper roots than herbs, such as celery or carrots, your raised garden bed should be approximately 12 inches deep. It’s not always easy to remember exactly what type of produce needs 12 inches versus something deeper, so do yourself a favor and make your raised garden bed 12 to 18 inches deep. This will ensure you can plant a wider variety of produce in the same bed.
Examples of vegetable roots with shallow roots that require a depth of 12 to 18 inches include radishes, broccoli, cabbage, cauliflower, Brussels sprouts, corn, potatoes, and chives.
Plants with Medium Roots—18–24 inches
Plants that grow roots between 18 and 24 inches into the soil will require garden beds with this depth to ensure they have enough room. Examples of produce that will thrive with this raised garden bed depth include cucumbers, beans, summer squash, and cantaloupe (if your cucumber leaves are turning yellow, see our guide here).
Plants with Deep Roots—24–36 inches
If you’re planting vine crops, such as winter squash, you’ll need to accommodate their roots, which can grow 24 to 36 inches into the soil. Other examples of produce that require a deep garden bed include watermelons, pumpkins, tomatoes, okra, and sweet potatoes.
What Happens if your Raised Garden Bed is Too Shallow?
If you don’t give the produce you’ve planted in a raised garden bed enough depth, you’ll end up with plants that fail to grow because there won’t be enough space for their roots to stretch out and gather nutrients from the soil.
They also won’t have adequate drainage, which will cause water to accumulate in the soil and become too soggy, damaging your plant roots. Waterlogged roots can also lead to root rot, which can kill your plants.
You also need to take care to ensure a deep enough raised garden bed if it’s built on a patio or other hard structure. The garden bed has to be deep enough for your plants to grow downward without being obstructed by the structure, especially if you’re planting produce that requires extra depth.
Note that when determining the depth of your raised garden bed, you’ll have to take the type of soil you’re using into consideration too. If your soil absorbs a lot of water, such as heavy clay soil, you should make your bed a bit deeper so that you encourage better drainage for your plants.
What Happens if your Raised Garden Bed is Too Deep?
If your raised garden bed is very deep, it could collapse—wet soil becomes heavy. You will therefore have to make provisions for the sides of the garden bed, to prevent them from breaking, such as with the use of cross-supports. Read Types of Potting Soil Explained to learn more about this.
Having a deep bed is also problematic if your plants don’t require extra space. Their roots won’t be long enough to absorb the nutrients, oxygen, and water they require to grow.
Finally, if your produce doesn’t require a lot of depth to accommodate its roots, you’re going to have a lot of soil going to waste. This isn’t practical and can waste your time and money. To learn more about potting soil, read our guide on choosing the best potting soil.
If you’re interested in growing herbs and veggies at home, you’ll need to set up a raised garden bed.
After reading this article, you’ll know how deep you should make your raised garden bed, depending on the type of produce you’re hoping to grow. We’ve also looked at why a bed that’s too shallow or too deep can cause you problems.