How Deep Should a Raised Garden be?

How deep should a raised garden be? There are 2 different types of raised gardens. The depth of your raised garden depends on the type you’re building. I’ll outline the things you should consider, with minimum depth guidelines for each style of raised garden.

How Deep Should a Raised Garden Be?

The simple answer is, the deeper the better. The best answer is that it depends. There are generally 2 different raised gardens:

  1. Raised gardens where the plants’ roots DO grow into the soil beneath (in-ground)
  2. Raised gardens where the plants’ roots DO NOT grow into the beneath (above-ground)

In-Ground Raised Garden

  • Roots DO grow into the soil beneath the raised garden bed.

This is the easier raised garden. The raised bed helps plants get established in nice, fertile soil that you’ve added. Once the plants get growing, their roots will grow down into the natural soil beneath the raised bed.

How deep should this raised garden be? 4″ minimum. However, the deeper the better.

This type of raised garden works really well because your plants get a good start to life and it’s easy for you to plant it. You’re also improving the soil in that particular spot because the soil and organic matter you add to the raised bed will filter down into the natural soil beneath.

If you ever move the raised bed, you’ll have a beautiful, improved in-ground garden underneath, which you can choose to plant in, or leave as-is, of course.

Example of a raised garden like this:

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Above-Ground Raised Garden Bed

  • Roots DO NOT grow into the soil beneath the raised garden bed.

This type of raised garden is enclosed, or you’ve added a barrier between the raised garden and the natural soil. If you can avoid this, I recommend you do so. Creating a stand-alone ecosystem makes it harder to get things right in your garden and it might cause problems with drainage, etc.

Many raised gardens you buy are like this, basically anything with legs and anything you “close off” to the rest of the garden. Like this:

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How deep should this raised garden be? 8 to 12″ minimum. However, deeper is better.

Remember that, in this type of bed, what you add is all your plants have. They can’t get their own nutrients or water, it’s up to you to provide them with everything. Enough soil to grow in comfortably, and enough fertilizer and nutrient.

How Big Should a Raised Garden Be?

The best size for the 2 types of raised gardens is the same. Around 4 feet wide is ideal for most vegetables, as well as other plants. You can reach every plant in the garden easily without stepping onto the soil or bending over excessively.

You can make them however long you like.

Build the beds in the direction that works best for your property. You might like to build one along a walkway or along the side of the house, for example. If you’re building in an open space, face them north-south. This gets the most sunlight to each plant in the bed. 

Why Raised Gardens?

why-raised-gardens

Raised beds can be beneficial in some circumstances. One of the main reasons to grow in raised beds in poor soil. If your soil lacks nutrients or is very sandy or full of clay, a raised bed can solve your problems. Raised beds can also look great, and you can put them wherever you like, even on stone or concrete. However, if you can grow in-ground, I recommend you do so. You can read my article: Why you shouldn’t grow in raised beds, for an overview of why that’s so. 

Advantages of Raised Bed Gardens

  • Soil. Raised beds are clearly defined gardens, so you can concentrate on that area for improving the soil. You can fill the beds with good quality soil and add lots of organic matter to create a beautiful growing environment.
  • Frost and sun protection. Plants can easily be protected from frost in a raised garden. It’s also easy to cover it with shade cloth for the sun in hot summers.
  • Earlier planting. Raised beds generally have excellent water drainage. Because of that, your soil warms up faster in spring, giving you a head start to planting.
  • Landscape improvement. Raised beds can look fantastic and you can place them anywhere, even on concrete.
  • Access. Raised gardens are great if you have back problems or other issues bending down. You can make them quite tall so they’re very easy to get to.

Soil for Raised Gardens

raised-garden-bed-soil

You can use your existing soil in a raised bed or you can buy soil to fill it. You can also use soil dug up from somewhere else. The one thing you want to avoid is a “soil line of change”. This is a distinct line where one soil ends and another starts. This line creates problems with root and water penetration. If you’re adding different soil to the raised bed, mix a bit of the natural soil with the new soil so there’s a gradual change.

I’ve always built raised gardens with the intention that eventually, plants’ roots will grow into the natural soil. In this case, it’s best to use soil that’s as close to the natural soil as possible. You could look into double-digging. In double-digging, you dig up the top 6” of soil and move it aside. Mix organic matter into the rest of the soil, then add the 6” back on top. The top 6” is your topsoil, the most nutritious part.

If your aim is to solely grow in the raised garden, without the plants’ roots growing into natural soil, you should aim for a sandier soil to assist drainage. Add lots of organic matter nonetheless!

Before you buy soil, remember that just because you can buy it doesn’t mean it suits your purpose. A commercial soil that’s made with manure can be high in salt, for example. Some commercial planting soils are too light for raised gardens and won’t hold water at all. That causes a nightmare situation where you’re constantly fighting against your soil drying out. Once it dries out, there’s no re-wetting it without serious intervention.

So, the answer to: “How deep should a raised garden be” depends on a few things, but, hopefully, this has given you an overview of what to aim for. Always mulch deeply in your gardens, mulch is one of the most important things to do. If you have any questions or tips about raised gardens, please leave a comment!

Last update on 2020-05-30 / Affiliate links / Images from Amazon Product Advertising API

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