Raised garden beds: how to build and maintain - Which? (2024)

Raised beds allow you to improve your garden soil, or even grow crops where there’s no soil at all.

Most people use wooded-sided beds, but you can create a raised bed by just putting a thick layer of garden compost on the soil and topping it up every autumn.

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The advantages of raised garden beds

The main advantage is that when your soil is poor that extra 15cm of soil that the raised beds provide makes all the difference, particularly as it’s topped up with soil improver regularly. The surface dries out and warms up quicker in spring, so you can also get ahead with early sowings.

The growing areas are differentiated from the paths, so the soil in the beds remains loose and easy to plant into. The paths can be mulched with wood chips and kept weeded. Most raised beds are no wider than 1.2m as this allows you to reach into the centre of the bed from the sides when planting, weeding, watering and harvesting so you don't ever need to tread on the beds. This width is also easy for you to protect from insects with fine mesh or from cold with fleece.

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Raised garden beds: how to build and maintain - Which? (1)

If you want raised beds on a hard surface, raise the sides to at least 30cm or preferably higher to give plants a decent depth of soil. Taller raised beds are also useful if you have trouble bending or kneeling, or garden from a wheelchair.

The wooden sides can be a hiding place for slugs and woodlice so be vigilant.

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Best Buy raised garden beds

Raised beds kits are increasingly popular for growing vegetables because they look neat and can make cultivation easier. You can make your own, but if that seems like a challenge too far there’s such a huge choice of kits it can be hard to know what type you should go for. Our Best Buy are the most robust beds that gave the best results.

Best raised bed kits

When testing raised bed kits, we looked for the products that were easy to build, robust and attractive. They also had to give us a great crop of veg.

Which? members canlog innow to see the full results and which are our Best Buys. If you’re not a member, join Which?to get instant access.

ProductOverall scoreInstructionsEase of constructionStructural strengthAppearance of bedEase of usePotato conditionPotato weightFinal condition*
Forest Garden Caledonian rectangular raised bed, wooden








Forest Garden raised bed builder pack, wooden








Garden Gear Original Veggie bed, metal









Garden Life metal raised garden bed kit








Garden Skill Build a bed 250mm raised bed kit, plastic









Greena Rectangular raised bed, wooden









Harrod Horticultural Allotment wooden raised bed kit, including capping









Overall rating The more stars the better. Ignores price and is based on: Clarity of instructions, 5%; Ease of construction, 10%; Structural robustness, 20%; Appearance of bed, 10%; Ease of use, 15%; Potato condition, 10%, Potato weight, 10%; Final condition, 20% *The condition one year after being constructed

Best materials for making a raised garden bed

You can buy ready-made raised beds, but if you want to save money, you can build your own bed.

Which? Gardening magazine trialled making beds from different materials to see how they compare.

Only Which? members cansee the full results of the two materials on test.

Material one and material two will be revealed once you log in.

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Material one

Material one pros:

  • The long length of this material meant that we only had to buy two to cut down for the size of our beds.
  • At 23cm-wide, they were also bigger than most of the other materials we tried. This gave the bed a good depth of soil to plant in to.
  • The bed looked strong, and when first built it gave the impression it would last for years.
  • The material faded a bit in the 18 months they were outside, but the only sign of deterioration was a bit of movement away from the fence post in one corner.
  • This bed gave the best yield of vegetables, particularly potatoes.

Material one cons:

  • This material were among the heaviest to work with.
  • The visual appeal of the otherwise chunky and robust-looking beds was also reduced.
  • The long length of the material makes it difficult to get home in a car, so you may need to pay to have them delivered.

Material two

Material two pros:

  • Inexpensive
  • As they were already sold in the length we required, we didn’t need to cut them down to size.
  • They were solid enough to screw together without needing a corner post. This reduced the installation time.
  • This material was easy to screw together and created a solid bed with a good depth of soil to plant in to.
  • The construction was solid and the material showed no signs of rot, warping or soil seepage, even after 18 months.
  • The yield of crops was satisfactory.

Material two cons:

  • You’ll need a long drill bit to create the pilot holes to screw together this material.
  • The thickness means the bed takes up slightly more space and also reduces the internal planting area.
  • The bed retained moisture well, but made the soil a bit wet and heavy to dig in spring.
  • Delivery charges for this material can be high.

Tips for making a raised garden bed

Raised garden beds: how to build and maintain - Which? (3)
  • Although 15cm is typically considered a reasonable height for a raised bed, you might prefer to build out of a slightly wider plank, which will give you a bit more depth of soil.
  • Strong corners helped to keep our beds in good condition – use 10 x 10cm fence posts rather than thinner battens to build a strong structure that will last.
  • Use screws rather than nails to build your bed. Nails will pull away from the corner posts more easily.
  • Restrict the width of your bed to 1.2m to ensure that you can easily reach the plants in its centre without having to stand in the bed.
  • None of the prices for our beds include the cost of delivery for materials. This ranged from £7.50 to £55, so is worth factoring into the cost of your project if you can’t collect the materials yourself.

What to fill raised garden beds with

Choose the wrong filling and you can end up with a bed that’s saturated in wet weather and slumps to create a compressed, airless mass with a hard crust that’s tricky to dig, or a mix that is so free-draining that your plants become parched in dry weather.

Which? Gardening magazine trialled different soil mixes to find the best recipe.

Best soil mix for raised garden beds

The best soil mix

  • Log in orjoin Which?to reveal the soil mix.
  • This mix excelled in most areas, giving us the biggest and healthiest-looking plants and best yields of potatoes and baby carrots.
  • Although the mix was quite heavy to put in the bed, it did not settle much and was very easy to dig.
  • It was easy to weed by hand without leaving roots behind. Soil fertility was good, and the pH around neutral.
  • The amount of moisture in the mix was well balanced, and it also had the warmest soil temperature – on average 1.5°C warmer than the ground temperature in the early part of the year

A soil mix worth considering

  • Log in or join Which? to reveal the soil mix.
  • They settled the least between autumn and spring, and the soil was on average 1.3°C warmer than the ground.
  • The mix also had a more neutral pH of 7.4than soil-only, and was just a little low in phosphorus when we tested it in the autumn.
  • The beds were easy to dig and weed, but could be drier than our best mix.
  • The yield of carrots was average, but the yield of potatoes was good.

The worst soil mix

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  • The average temperature was barely warmer than the ground, and it became so wet and heavy during the soggy spring that we had to delay planting our potatoes until it was workable.
  • Weeds snapped off when pulled, leaving their roots behind.
  • Soil fertility tests in autumn revealed that the soil had an alkaline pH of 7.9 and was lacking in nitrogen, phosphorus and potassium.
  • Despite adding NPK fertiliser in spring, the plants looked smaller and paler in these beds and produced the lowest yield of potatoes and carrots.

Discoverhow to grow a range of different veg

Raised garden beds: how to build and maintain - Which? (2024)

FAQs

What do you put in the bottom of a raised garden bed? ›

Depending on your budget and gardening goals, you can line the bottom of your raised garden beds with wide-mesh hardware cloth, stainless steel mesh, landscape fabric, burlap sack, or newspaper/cardboard.

How deep should a raised garden bed be for tomatoes? ›

Tomatoes should ideally be grown in a raised bed that's at least 15 to 18 inches deep. Many of my clients in Houston are successfully growing tomatoes in 12-inch deep raised garden beds, but their plants tend to be a little stunted compared to plants in deeper beds.

Should I put landscape fabric under 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.

How do I protect my raised garden bed from pests? ›

Placing something in and around your garden bed that physically stop pests from getting to your plants is one of the soundest protections where practical. Common barrier materials include collars, fabric, fencing, mesh and more. While they sound expensive, some of them can be homemade from waste materials.

Why put cardboard in raised beds? ›

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 rocks in the bottom of my raised planter? ›

Adding rocks to the bottom of a raised bed makes it challenging to amend or improve the soil over time. It restricts access to the lower layers and can impede the addition of organic matter or nutrients. Over time, rocks will get mixed in with your raised bed soil, not cool! Rocks are expensive and heavy!

What is the best filler for the bottom of a raised bed? ›

The materials used include large rotting logs, sticks and other debris that are layered with grass clippings, coffee grounds, compost, and other organic matter. As the material breaks down, it creates a flourishing environment for beneficial fungi and microbes that mimics the natural landscape of a forest.

What are the disadvantages of raised garden beds? ›

Water Usage and Seasonal Considerations - Due to a raised garden's superior drainage, they tend to dry out faster in the warmer months. This requires more frequent watering to keep your plants hydrated. Due to the increased air circulation, raised beds can become colder sooner than natural soil.

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

As a rule of thumb, a 4'x8' raised bed that is 6 inches deep requires approximately 8 bags of soil while a 4'x8' raised bed that is 12 inches deep requires approximately 16 bags of soil.

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.

Do tomatoes like top soil or potting soil? ›

Tomatoes can thrive in pots as long as they are grown in high-quality potting soil and receive plenty of sun, water and fertilizer.

How deep does a raised bed need to be for cucumbers? ›

Medium-rooting vegetables like kale, cucumbers, and zucchini love at least 18 inches. A 2-foot bed is ideal for these types of vegetables, as well as fruits that grow on bushes like blueberries, strawberries, and raspberries.

How far apart do you plant tomatoes in a raised bed? ›

Plant them at 18- to 24-inch spacing. Don't worry about letting the plants lean to one side; in a few days, they straighten up on their own. Water tomatoes at planting and regularly while growing to avoid blossom-end rot, which is caused when the soil is allowed to dry out.

How often should I change the soil in my raised garden bed? ›

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.

Do raised beds need to be treated? ›

The key to longevity is treating these wooden raised beds properly in the first place. There are some great products on the market and you should try to use one of these before you fill in the space with soil. You can do it after but you'll have a much easier time if you do it before!

Do raised beds need compost every year? ›

If your soil has high levels of phosphorus, take a break from applying compost for a few years. But if your soil test indicates that your soil phosphorus levels are not excessive, then go ahead and add compost. We typically recommend about an inch or less of compost over your garden beds each year.

How often do you water a raised bed? ›

Ideally, you should water an in-ground bed 1 to 2 inches a week, while a raised bed may require more water per week. Feeling the soil frequently is the best way to gauge when a raised vegetable bed needs watering.

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