HiddenFromTOCWhat is the best soil for raised garden beds?
- The right soil can have a huge impact on the health and happiness of your plants, improving their resistance to diseases and leading to the higher yield.
- Most gardeners find a mixture of 60% topsoil, 30% compost and 10% potting soil is sufficient for most raised beds, although this does depend on what you are growing.
- There’s a number of ways to improve your raised bed soil. Adding compost, soil amendments or fertiliser can improve the structure and quality of the soil in your raised bed.
One of the key benefits of a raised garden bed is that they allow you to tailor the soil to suit whatever you’re growing. Any gardener will know that the soil can make an enormous difference when it comes to the health of your plants, and the great thing about raised beds is you can fill them with the perfect blend.
The right soil is the first step towards a thriving raised bed garden!
Not sure what to consider when it comes to the best soil for your raised garden beds? This post will tell you all you need to know.
The Advantages of a Raised Bed Garden
Raised beds allow you to tailor the soil to suit whatever you are growing. Different plant have different soil requirements. While some prefer more acidity, others thrive in a more alkaline blend. Likewise, while some plants need very good drainage, others prefer to be in a soil that retains water.
For those with naturally poor soil in their garden, installing raised beds can help enormously. You are able to fill the bed from scratch if needed, or you can add mulch and organic material to the existing soil in your garden to improve its quality.
The ability to control the soil isn’t the only advantage of a raised garden bed. Raised bed gardens are more space-efficient than in-ground gardens. They allow you to grow more in a smaller area as, thanks to the improved soil quality, there’s usually more nutrients to go around.
Why is Garden Bed Soil so Important?
One of the most important factors when it comes to successful gardening is the soil quality. While many plants are able to grow in poor soil, most of the plants we want to grow in our garden thrive in good-quality, nutrient-rich soil.
As a result of better quality soil, you’ll likely see increased resistance to fungal diseases, better drainage and a higher yield. Soil with good drainage will warm faster in the spring, meaning you should be able to start planting earlier in the year.
What Makes Soil ‘Low Quality’?
When we talk about soil quality, we are usually referring to the levels of available nutrients, as well as the structure.
The structure of the soil will determine how easily water and essential soil nutrients are retained. Nutrients and water which are retained in the soil will be easily picked up by plants.
Low quality soil on the other hand is usually:
- Too sandy
- Contains too much clay
Sandy soil consists of very large particles. These particles allow water and nutrients to drain through before they can be taken in by the plant. Clay soil, on the other hand, is more compact. With very little space between the particles, water and nutrients aren’t able to get through. You may find that they sit on the top of the soil, leading to puddling around the plants.
Poor quality soil can result in diseased crops and a poor harvest. If the quality of your soil is decreasing, the soil is often to blame.
What Makes Soil ‘Good Quality’?
Good quality soil is usually described as being ‘loamy’. This type of soil is made from a balance of sand, silt and clay. It has a crumbly texture that gets sticky when wet. This soil can be easily separated, meaning small pockets can form within. Water and nutrients can be stored in these pockets, able to be picked up by the plant when it needs them.
The Best Soil for Raised Garden Beds
Some gardeners use their native soil for raised beds. While this can still work in many cases, raised beds provide you with an opportunity to create a specific soil that’s tailored to whatever you are growing. Most gardeners will see a big difference in their plant health and yield if they tailor the soil in their raised beds.
So, the best type of soil for your raised beds depends on what you are growing. While some plants thrive in acidic soil, others prefer soil with a higher pH.
The amount of rainfall your region gets will also impact your soil choice. If your area sees very hot, dry summers, you’ll need a soil with good moisture retention. In wetter areas, soil with good drainage is more important.
For most situations, the following raised bed soil mix is recommended:
- 60% topsoil
- 30% compost
- 10% potting soil (for example, perlite)
If you haven’t got a good quality topsoil, a mix of equal parts potting soil and compost is also sufficient.
How to Improve your Raised Bed Soil
Different methods of gardening can help you to improve the soil in your raised bed. In fact, some of these techniques can be used to fill your raised bed completely.
Hugelkultur Method
An inexpensive and effective way to fill your raised bed with good quality matter is to use the Hugelkultur method.
Instead of filling the bed with pre-purchased soil, this method involves using layers of organic matter which can be sourced very cheaply.
Being by adding layers of organic material to the bottom of the raised bed. This can be matter sourced from your garden, including logs, branches, grass clippings and leaves. You can also use food waste such as coffee grounds or vegetable scraps. Build up these materials in the bed, leaving a 6″ gap at the top.
Fill the remaining 6″ of the bed with a combination of potting soil and compost.
The lower layers of the bed will slowly break down to form a nutrient-rich soil. For the first year of planting, it’s a good idea to choose plants with a shallow root system.
Once the material at the bottom of the bed has broken down, you can grow plants with larger root systems, adding more soil to the top of the bed if needed.
Adding Compost to the Raised Bed
One of the most reliable ways to improve the soil in your raised bed is to add compost.
Compost can be added at the start and end of the gardening season, in both the spring and autumn months. It offers a number of benefits to your raised beds, helping to enrich the soil and improve moisture retention. Compost can also help improve your plants’ resistance to diseases.
You’ll be able to grow more plants in a smaller area, as the improved soil health means there’s more nutrients available to go around.
Composting is also a great way to make use of kitchen waste that would otherwise be thrown away. Food scraps, coffee grounds and organic matter from the garden can all be loaded into a compost bin and left to break down.
Adding Soil Amendments
If you are planning on using your native garden soil in your raised beds, soil amendments can be added to improve the quality.
Soil amendments can:
- Change the soil structure
- Increase the number of nutrients in the soil
- Alter the pH of the soil
Some of the most commonly used soil amendments are perlite, coir, worm castings and animal manure.
Perlite changes the structure of the soil, subsequently improving its drainage. It allows excess water to drain away, while catching and holding onto the nutrients which plants require.
Coco coir can be added to the soil to aid drainage and improve aeration. This amendment has a high water holding capacity, so it’ll keep hold of water that’s needed, allowing the excess to drain through.
Worm castings can increase the water retention of the soil, improve aeration and help the soil to keep hold of nutrients which would otherwise leach away. Worm castings break down over time, releasing nutrients into the soil as they do so.
Amendments can also be used to alter the pH of the soil. To make the soil more acidic, you can add sulphur. To make it more alkaline, add dolomite or wood ashes.
How Much Soil Do you Need?
Knowing the length, width and depth of your raised bed will allow you to work out exactly how much soil you need.
Different plants have different depth requirements. If you’re planning on having a raised bed vegetable garden, a depth of 12″ to 24″ is sufficient. For herbs and many flowers, a depth of around 11″ should be enough.
Bear in mind that raised beds which are very low to the ground can be harder to maintain if you have mobility issues, a lot like traditional in-ground garden beds.
To calculate the volume of soil you require you should:
- Measure the length, width and height of your raised bed, each in the same unit (feet or inches)
- Times the length by the width and the height (L x W x H)
The result is the cubic volume of soil you require.
Raised Bed Soil FAQ
Should I use topsoil or compost for raised beds?
Ideally, you should use both. A mixture of topsoil and compost together makes a good quality soil for raised beds.
What’s the difference between garden soil and raised bed soil?
Raised bed soil should be much more nutrient-rich than standard garden soil. As raised beds dry out faster, the drainage is also more important.
If you want to use your existing garden soil in your raised bed, you could mix it with potting soil and organic compost to improve the quality.
How do you fill a raised bed cheaply?
There’s a number of ways to fill a raised bed on a budget. Different methods of gardening such as the Hugelkultur method, Lasagna method and the Ruth Stout method are all very effective.
We’ve written an article that talks through the best ways to fill a raised bed on a budget.
How often do you need to change the soil in raised beds?
A lot of experts recommend replacing the soil completely once a year for best results. However, replacing all the soil is often necessary. Instead, the soil may simply need a refresh.
You can refresh your soil in a number of ways:
- Add compost to the raised bed
- Use soil amendments such as coco coir or perlite
- Add an organic fertiliser
So long as the plants growing in your raised beds are healthy and free from pests, it’s fine to reuse the soil the following year.
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