How Deep Should a Raised Garden Bed Be | Expert Advice

The depth of the raised garden bed is one of the main considerations when building a raised garden bed. It can significantly impact development and crop yields. If the bed is too shallow, the plant’s roots may not grow deep enough to get the nutrients they need. On the other hand, if the bed is too deep, it may be difficult to maintain, and soil compaction may occur. 

So, how deep should a raised garden bed be? Determining the correct depth requires considering the needs of the plant and your personal needs. This article will answer the question and mention how to calculate the ideal depth for a raised bed.

How Deep Should a Raised Garden Bed Be?

There are various things to consider when determining the depth of your raised garden bed. 

• Plant Selection: Carefree plants or those with shallow root systems, such as alpine herbs, poppies, sedums, and lavender herbs, require a bed depth of at least 6 inches, according to gardening expert Fiona Jenkins. However, a raised bed depth of at least 12 inches is necessary for other plants, including perennials, small shrubs, and vegetables.
• Soil Quality: The depth of your raised bed is closely tied to the soil quality you use. Having a deeper raised bed can be advantageous if your garden is in cases of heavy clay or poor soil. 

It provides more space for well-draining and nutrient-rich soil, strengthening plant root systems. Strong root systems are essential for healthy plant growth, as they allow plants to access water and nutrients more effectively, leading to better overall growth and productivity.

• Climate and Rainfall: Deeper beds can better retain moisture in regions with high evaporation rates, which reduces the need for regular watering and promotes plant growth. In areas with frequent rainfall, deeper beds can also aid in preventing waterlogging by providing more space for excess water to drain away.

• Drainage: A raised bed should be at least 8 inches deep since most plants need at least 6’’ to 8’’ of soil depth for optimum root growth. However, for plants that prefer drier soil or in areas where drainage is an issue, a taller bed filled with a porous growing medium may be necessary.
• Material: Metal panels can rust over time, wood can rot quickly, and stone and concrete blocks can be expensive to install. Land Guard Galvanized Raised Garden Beds offer a solution with their rust and corrosion-resistant metal and easy-to-assemble kits, providing a durable and attractive option for raised bed gardens.
• Double Digging: Double digging is a process by which some gardeners use shovels to create more space for roots, especially if they have a crowded or shallow garden bed. But this way can be time-consuming and arduous. With Foyuee Galvanized Raised Garden Beds, the tall design allows for placement anywhere without the need to dig into the ground.
• Vegetable Beds: When it comes to vegetable beds, a depth of 12-18 inches is recommended to ensure proper root depth for plants. This is especially important if the bed is placed on cement or a patio, as it can inhibit root growth. Outdoor Metal Raised Garden Beds, which are available in depths of 17″ and 32″, provide adequate room for a range of vegetables with deep root systems while also holding moisture and minimizing the need for regular watering.

Below is a table listing raised garden bed heights for plant species. Take some time to examine the height of your raised bed to get a better idea of ​​whether it will be suitable for the typical types of plants you want to grow:

Heading Plant Arrangements

When planning the components of a raised bed, it is important to align the plants so that taller plants do not block sunlight from smaller plants. Beds should be facing south horizontally, leading to optimized sunlight exposure throughout the bed and preventing neighboring plants from shading each other when the sun moves from east to west. 

If you grow many types of plants, you can orient the bed vertically (north to south) and place taller plants at the back to prevent them from shading smaller plants. Do not place garden beds in windy, wet, and swampy areas.

Knowing the height of each crop at maturity is important in planning out your planting arrangements. For example, shorter plants such as lettuce and radishes should be planted on the area’s south side, while the tallest plants should be planted on the north side of the area. If you have a trellis, it’s essential to place it close to the back wall, as these plants can block a lot of light. 

To help you figure out your planting arrangements, here are the mature heights of some common vegetables:

Bending Over

If you have mobility issues, back strain, or just don’t like bending over, a taller raised bed will improve your gardening experience.  OLLE Extra-tall 32-inch Galvanized Raised Garden Bed significantly reduces back stress when tending or harvesting your garden. Whether you are an experienced gardener or a beginner, we definitely recommend investing in a raised bed to reduce stress on your back for your health.

Drawbacks of Using Shallow Raised Beds

Shallow beds are often known for their convenience and beauty, but they also have some drawbacks. Although they are a popular choice for gardeners looking for a convenient and tidy garden solution, it is important to consider their disadvantages before using them.

• Limited Root Space: One of the major disadvantages of shallow raised beds is their limited depth. This implies that plants with deep root systems, such as carrots or potatoes, may struggle to thrive and reach their full potential. Root-bound plants can cause stunted growth and reduced yields.
• Regularly Water: Shallow seedbeds will dry out faster than deeper seedbeds. This requires more frequent irrigation, which can be time-consuming and lead to increased water consumption, especially in arid areas.
• Nutrient deficiencies: Shallow soil beds deplete nutrients faster than deeper soil beds, requiring more frequent soil amendments and fertilization. 
• Temperature fluctuations: Shallow soils heat up and cool down faster than deeper soils, which can stress plants, especially during extreme weather conditions. This can lead to unstable growing conditions.
• Invasive weeds: Shallow seedbeds are generally more vulnerable to invasive weeds because weed seeds can germinate and develop more easily in shallow soil depths. This main reason comes from reduced competition from other plants.
• Limited plant diversity: Some plants with deep root systems, such as deep-rooted fruit trees, are unsuitable for shallow, high beds. This restriction may limit the choice of plants you can grow.

The Benefits of Using Appropriate Raised Garden Beds

When you use appropriately raised garden beds, they offer you a variety of benefits, making work efficient as well as crop yields.

• Improved soil quality: Gardeners have greater control over soil composition and quality by putting soil into a raised structure. This method allows for optimal drainage, aeration, and nutrient supply, resulting in healthier plant growth and higher yields.
• Reduces weed growth: The raised design makes it difficult for weeds to invade garden beds, reducing the need for frequent weeding and minimizing competition for nutrients. 
• Better pest control: Elevated structures make it more challenging for many ground-dwelling pests, such as slugs and snails, to access your plants, reducing the risk of damage. 

What Do You Put In The Bottom Of A Raised Garden Bed?

There are many types of materials being placed in the bottom of a raised garden bed. You should consider adding a layer of coarse gravel or small stones. This helps with drainage and prevents standing water and root rot.

Furthermore, you can add a mixture of high-quality soil and compost to create a nutrient-rich environment for your plants to flourish on top of the drainage layer.

You can also put plastic bottles or garbage bags as filler at the bottom of the raised bed to save on soil, but this defeats the purpose of giving the plant’s roots the space they need to grow. Make sure your raised beds are filled from bottom to top with organic materials that nourish your plants rather than materials that will slowly break down and contaminate the soil with plastic particles.

Before shoveling in new soil, place some weed-blocking fabric at the bottom of the bed to keep weeds out and prevent the soil from washing away during the first heavy rain. If you have pests that like to dig out of the ground and eat your plants, add a metal mesh barrier as well.

How much soil do I need to fill a raised bed?

Here’s a simple soil calculator to help you calculate exactly how much soil you need to fill your raised garden:

• Step 1: Calculate the total width of the garden in feet = W
• Step 2: Calculate the total length of the garden in feet = L
• Step 3: Calculate the total height of the garden in feet = H
• Step 4: Multiply the three together: Width x Length x Height (W x L x H)

The answer to this equation is the total number of cubic feet of soil required for the raised bed.

Example:

In your garden, there are six raised beds, and each one measures 3 feet in width, 8 feet in length, and 2.5 feet in height.

To calculate cubic feet per bed, we used a soil calculator: 3 x 8 x 2.5 = 60 cubic feet per bed.

Since this setup consists of six gardens of the same size, the total calculation for the total amount of soil required for these raised beds is 6 x (3 x 8 x 2.5) or 6 x (60) = 360 cubic feet.

Making Accessible Garden Bed

The 2-foot raised beds are ideal for working in the garden from a chair or wheelchair without having to bend over. An open plan with 2-foot-tall raised beds or widely spaced rows of beds can form the basis of a social gathering place for people in assisted living or can be part of a functional and accessible community garden plan.

The best height for a raised bed is based on your vision of where and what your bed will accommodate. A beautiful flower box or delicious herb garden is perfect for the one-foot durable outdoor raised bed.

When it comes to more room for plant roots, a stunning vertical touch to your outdoor space, and better drainage options, 2-foot raised beds are the best choice. A little more fertile soil doesn’t hurt, and a little less stooping in the garden certainly doesn’t hurt either. If you have plants with deep roots or if wheelchair accessibility is the key factor, a depth of 2 feet is necessary.

Final Thoughts: What Is the Ideal Raised Bed Size?

The depth of a raised garden bed is based on the type of plants you want to grow and other related factors. Generally, you should aim for at least 12” of soil depth for most crops and up to 36” for plants with longer roots.  “How deep should a raised garden bed be?” depends on a number of factors, but hopefully, this overview has helped you determine what to aim for. Therefore, it is important to consider how deep your raised garden bed should be before you start building it.