How to make a raised bed / RHS Gardening (2024)

Raised beds - frequently asked questions

What other materials can be used to build a raised bed?

Timber is the most popular material for constructing raised beds, but there are several other options:

Stone: both natural stone and stone prepared for wall construction can be used. Skilled labour is usually required for construction and footings are nearly always required (see 'Top tip' below).Generally the most expensive material.

Brick: strong, durable and can be used to create curved beds. Skills are needed for construction and footings are generally required (see 'Top tip' below). Engineering bricks are the most suitable as they are weather resistant. Domestic bricks are much cheaper but porous and therefore less durable.

Top Tip

Raised beds built with masonry walls (stone or bricks) higher than 20cm (8in) should be bonded with mortar and laid on concrete footings approximately 15cm (6in) deep and 30cm (1ft) wide. These footings should sit atop hardcore foundations 15cm (6in) deep.

If you plan to grow ericaceous (acid-loving) plants in a masonrybed, make sure to line it with recycled plastic to separate any lime in the mortar from plant roots.

Paving slabs: can be inserted on their side to create a reasonably deep and inexpensivebed with one layer. At least 15cm (6in) of slab needs to be buried in the ground for stability, leaving 45cm (18in) above soil level. As paving slabs often move over time, 30cm (1ft) deep concrete haunchings can be laid for extra stability, and metal plates fixed at each vertical joint.

Recycled plastic: several companies now offer 'sleepers' made from recycled plastic bottles. Different colours are available and some are finished to look like timber. Extremely durable and maintenance free, but fairly expensive and only available in certain sizes.

Can I build a raised bed on a hard surface?

Yes, but it's important to adjust the bed design and soil mixture to ensure good drainage and avoid problems with waterlogging. If constructing the bed from timber, drill plenty of holes in the sides of the bed to allow excess water to drain away. For beds made of stone or brick, leave gaps at 45cm (18in) intervals between the joints in the first two courses to act as drainage holes. Cover these on the inside of the bed with fine wire mesh, and heap gravel against the mesh when filling the bed, to prevent soil clogging them up.

Fill beds constructed on a hard surface with amixture of three parts organic matter, four parts sharp sand and seven parts topsoil. Be prepared to refresh and replace the soil regularly, as you would when repottinga large container, to maintain good drainage.

How to make a raised bed / RHS Gardening (2)

Will I have to water more?

Plants in raised beds tend to suffer more quickly and more severely from drought than plants growing in the garden soil, owing to improved drainage, so it's important to keep an eye on watering needs. As with watering containers, it's a good idea to regularly check the moisture level about a finger's depth below the soil surface to see if additional watering is needed, and be prepared to water more following warm and windy weather when plants lose water more quickly.

If you're finding the soil is often dry, or your plants are showing signs of stress, add a layer of mulch to the surface of the beds to help conserve moisture.

Will fungi grow on my raised bed?

Saprotrophicfungi can colonise and rot down untreated timber, which softens it over time, so you may need to undertake occassional repairs to keep beds structurally sound if you use this material. However, spongy wood rotted by fungi creates valuable habitats for garden wildlifeand retains water, helping to regulate the moisture content of the bed. If you're happy to undertake repairs every few years, then using untreated wood, whole logs or even fungi logs is a great way to create little wildlife havens in your garden, and may even help keep plant health problems away.

However, if you are struggling to control honey fungus in your garden, it may be best to steer clear of using timber to construct your raised beds and choose masonry or recycled plastic instead, in case the wood acts as an additional food source for the fungus.

How to make a raised bed / RHS Gardening (2024)


How do you prepare a raised bed for gardening? ›

How to fill a raised garden bed in six simple steps
  1. Step #1: Prepare your garden bed. ...
  2. Step #2: Add a drainage layer. ...
  3. Step #3: Add a layer of ordinary garden soil. ...
  4. Step #4: Add some premium potting mix. ...
  5. Step #5: Water the soil to help it settle & add some mulch. ...
  6. Step #6: Start planting!
Jan 30, 2023

How many bags of soil do I need for a 4x8 raised bed? ›

For a 4x8-foot raised bed with a 6” height, using Mel's Mix: about 5 cubic feet each of compost, peat moss, and vermiculite is needed. It usually takes about two to three bags of purchased fertile mix (1.5 cubic feet each) to cover the bed surface to a depth of 2 inches.

What are three mistakes to avoid when gardening with raised beds? ›

Seven Beginner Raised Bed Gardening Mistakes to Avoid
  • Picking The Wrong Spot.
  • Not Thinking About The Water Source.
  • Raised Beds Placed Too Close Together.

Should I put landscape fabric under a raised bed? ›

Landscape fabric is beneficial for raised garden beds, here are just a few of the many reasons why you should use landscape fabric for raised bed gardening: Prevents soil erosion in a raised bed: As a liner, landscape fabric lets water drain away from the soil while leaving the soil intact.

What is the easiest thing to grow in a raised bed? ›

If you're looking for high-yield veggies, you can't go wrong with cucumbers, pole beans, radishes, squash, zucchini, peas, and tomatoes. These vegetables are easy to grow and have been known to produce a large amount of produce per plant, providing you with a bountiful harvest that lasts for weeks.

What should I line my raised veg bed with? ›

Plastic (non-porous liners / damp-proof membranes)

High-quality plastic damp proof membranes offer the best type of protection for your raised bed. This type of liner will ensure your structure stays in great condition.

Should I put rocks in the bottom of my raised garden bed? ›

A: You should avoid putting rocks in the bottom of your garden bed. A common myth is that this will improve drainage. Instead, this can actually increase water saturation levels as well as allow gravel to mix in with your soil, which can prove very difficult to remove later on.

How deep should a raised bed be? ›

The minimum required depth depends on the plant. But on average, a raised garden bed should accommodate about 20 inches of soil for the roots of flowers and vegetables.

How deep should a raised bed garden be? ›

Vegetable Beds: On the other hand, when it comes to vegetable beds, the bed must be approximately 12 to 18 inches deep to ensure adequate depth for the roots of your plants. This is especially important if your raised bed is placed on cement or the patio, which will inhibit roots from growing deeper into the ground.

What is the first layer of a raised garden bed? ›

1. Wood: Lay a thin layer of small twigs, branches, or bark at the bottom of your raised bed. You can also add other materials like newspaper and manure at this first step.

How to fill a raised garden bed cheaply? ›

To start, lay down sheets of cardboard or newspaper for weed suppression and then fill the raised bed structure halfway up with alternating layers of nitrogen-rich materials (like kitchen scraps and grass clippings) and carbon-rich materials (like wood chips and dried autumn leaves).

How often do you change soil in raised beds? ›

Ideally, we think it's best to consider replenishing the soil between each season i.e. after every Autumn/Winter and Spring/Summer harvest; however, if you can only do it once a year, that's alright too.

What is the mix ratio for raised beds? ›

Add a mixture of compost and purchased topsoil in a 1:2 or 1:1 ratio, to the top of the bed. There are vendors who sell topsoil mixed with compost. Alternatively, fill the bed with compost and a soilless growing mix in a 1:1 ratio.

Should I put cardboard in the bottom of my raised bed? ›

It acts as a physical barrier to block out pernicious weeds. Usually, 2 – 3 layers of cardboard will suffice, though you may want layers in more weed-prone areas. The damp environment created by the cardboard is conducive to earthworms and other beneficial soil microorganisms.

Should I put sand in the bottom of my raised garden bed? ›

A strong and stable base is essential for the health and productivity of your raised garden bed. By using the right materials, such as gravel, landscape fabric, sand, compost, cardboard, or soil, you can create a well-draining and nutrient-rich foundation for your plants.

Should I put sticks in the bottom of my raised garden bed? ›

PSA: It's completely fine to put logs, sticks, twigs, and garden scraps at the bottom of a raised bed to fill up space! ##garden. How to Build Raised Garden Bed.

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