Raised Bed Gardening Guide for UK Gardens

Why Grow in Raised Beds

Raised beds have several advantages over flat ground, particularly on the heavy clay soils that are common in parts of the Chilterns.

Better drainage

Raised beds drain faster than flat ground, which is useful on heavy clay. The soil in the bed warms up and dries out earlier in spring, allowing earlier sowing. In a wet year, raised beds keep the roots out of standing water.

Earlier spring

The soil in a raised bed warms up 2 to 3 weeks earlier in spring than flat ground, because it is above the surrounding soil level and exposed to the sun on all sides. This allows earlier sowing of vegetables and an extended growing season.

No soil compaction

Because you never stand on a raised bed, the soil stays loose and well aerated. Roots grow more easily, and the soil needs less digging. After the first year, raised beds are largely no dig: just top up with compost annually and let the worms do the work.

Higher yields

Raised beds typically produce 20 to 30 percent more per square metre than flat ground, because the soil is better, the plants are closer together, and the drainage and warming are superior. A 1.2 by 2.4 metre bed can produce a surprising amount of food.

Easier on the back

A 20 to 30cm raised bed means less bending when sowing, weeding, and harvesting. For gardeners with back or knee problems, raised beds make vegetable growing possible again. Beds built 60cm high allow gardening from a wheelchair.

Materials for Raised Beds

Pressure treated timber

The most popular material for raised beds. Buy 15 to 20cm wide boards, 5cm thick, in 2.4 metre lengths from a builders merchant. Pressure treated timber lasts 8 to 15 years in contact with soil. Cost: 10 to 15 pounds per board, so a 1.2 by 2.4 metre bed uses 3 boards and costs 30 to 45 pounds.

Concerns about the chemicals in pressure treated timber leaching into the soil are largely historical. Modern pressure treatment uses copper based preservatives that are far less toxic than the chromated copper arsenate (CCA) used until 2004. If you are concerned, line the bed with polythene before filling.

Scaffold boards

Second hand scaffold boards are 38mm thick and 225mm wide, which makes an excellent raised bed. They are stronger than ordinary timber and last longer. Buy from scaffolding suppliers or second hand from building sites. Cost: 10 to 15 pounds per board, similar to pressure treated timber.

Recycled plastic

Recycled plastic boards look like timber but never rot. They last indefinitely, need no treatment, and are environmentally friendly. The downside is the cost: 25 to 40 pounds per board, two to three times the price of timber. Worth it for a bed you want to last a lifetime.

Sleepers

New or reclaimed railway sleepers make substantial raised beds. They are 200mm by 100mm by 2.4m, and very heavy. New softwood sleepers cost 25 to 40 pounds each. Reclaimed hardwood sleepers are more expensive and may be contaminated with tar, so avoid them for vegetable beds.

Brick and stone

Permanent and attractive but expensive and skilled work to build. A brick raised bed costs 100 to 200 pounds per linear metre built. Best for ornamental beds in a formal garden, not for vegetable beds.

Kit form beds

Ready to assemble raised bed kits in timber, plastic, or metal are available from 40 pounds for a small 1 metre square bed to 200 pounds for a large 2 by 1 metre bed. They save the work of cutting timber and are a good option if you are not confident with a saw.

Raised Bed Material Comparison

Building a Raised Bed

Step 1: Choose the site

Pick a sunny spot for vegetables, at least 6 hours of direct sun a day. Level ground is easier, but a sloped site can be terraced. Avoid low spots that collect water. Check there are no underground pipes or cables where you plan to dig.

Step 2: Mark out the bed

Mark the corners with pegs and run a string line between them. Check the corners are square by measuring the diagonals, which should be equal. A standard bed is 1.2 metres wide by 2.4 metres long.

Step 3: Prepare the ground

Cut the grass short if there is lawn on the site. You do not need to remove the turf, just cover it with a thick layer of cardboard before filling the bed. The grass will die and decompose, adding organic matter. If the site is weeds rather than grass, dig out perennial weeds such as bindweed and couch grass first.

Step 4: Build the frame

Cut the timber to length: two boards 1.2 metres long and two boards 2.4 metres long. Use 5cm by 5cm timber posts in the corners as uprights, 30 to 40cm long, driven into the ground. Screw the boards to the corner posts with 60mm exterior screws. Check the frame is level with a spirit level, adjusting the soil underneath if necessary.

For beds longer than 2.4 metres, add intermediate posts every 1.2 metres to prevent the boards bowing. For beds two boards high, overlap the joints at the corners for strength.

Step 5: Line the bed

If you are using pressure treated timber and are concerned about chemicals, line the inside of the bed with heavy duty polythene. This also helps the timber last longer by keeping the wet soil off it. Leave the bottom open for drainage.

Step 6: Lay cardboard

Lay a thick layer of cardboard over the bottom of the bed, overlapping the edges by 15cm. This suppresses any weeds or grass underneath and decomposes over a year, adding organic matter.

Step 7: Fill the bed

Fill the bed with your soil mix (see below). Do not pat it down firmly, just level it with a rake. Water it thoroughly and leave for a week before sowing, to allow the soil to settle.

The Best Soil Mix for Raised Beds

The soil you fill a raised bed with is the single biggest factor in how well it performs. Do not just use soil dug from the garden, as it will compact and drain poorly. Use a mix of topsoil, compost, and drainage material.

Standard mix

60 percent topsoil, 30 percent compost (well rotted manure, garden compost, or bagged compost), 10 percent sharp sand or grit. This mix is free draining but moisture retentive, and rich enough to support vegetables for a season.

No dig mix

For a no dig approach, start with a 50/50 mix of topsoil and compost. Each year, top up with 5cm of compost. Over a few years, the soil structure becomes excellent and you never need to dig.

Budget mix

If you cannot afford to fill the bed with bought materials, layer what you have. Bottom layer: twigs and branches for drainage. Middle layer: lawn clippings, leaves, and cardboard. Top 15cm: a mix of topsoil and compost. The bed will be productive immediately and improve as the lower layers decompose.

How much soil do you need

A 1.2 by 2.4 metre bed, 20cm high, needs 0.58 cubic metres of soil mix, which is about 800kg. A bulk bag of topsoil is 1 cubic metre and costs 50 to 80 pounds. For two raised beds, you need about one bulk bag of topsoil plus compost and sand.

Buying soil in small bags from a garden centre is expensive. A 50 litre bag of topsoil costs 4 to 6 pounds, so a cubic metre costs 80 to 120 pounds. Buy bulk bags from a builder's merchant or soil supplier for half the price.

What to Grow in Raised Beds

Raised beds are ideal for vegetables, herbs, and cut flowers. The improved drainage and warmer soil allow earlier sowing and higher yields than flat ground.

Vegetables

• Leafy crops: lettuce, spinach, chard, rocket. Sow in succession for continuous harvest.
• Root crops: carrots, parsnips, beetroot, radishes. The loose soil is ideal for carrots, which fork in stony ground.
• Brassicas: cabbage, broccoli, kale, cauliflower. Need firm soil, so do not over dig the bed.
• Legumes: peas, broad beans, runner beans, French beans. Support with canes or netting.
• Alliums: onions, shallots, garlic, leeks. Easy and reliable in raised beds.
• Cucurbits: courgettes, pumpkins, squash. Need rich soil and plenty of space.

Herbs

Most herbs do well in raised beds, particularly Mediterranean herbs such as thyme, oregano, sage, and rosemary, which prefer the well drained conditions. Mint should be grown in a pot sunk into the bed, otherwise it will spread and take over. See our rosemary profile for more detail.

Cut flowers

Raised beds are excellent for cut flowers such as sweet peas, dahlias, cosmos, zinnias, and antirrhinums. The rich soil and good drainage produce long stems and abundant flowers.

What not to grow in raised beds

Avoid perennials that spread, such as mint and horseradish, unless grown in pots sunk into the bed. Avoid large plants that need a lot of root space, such as artichokes and asparagus, which are better in the open ground. Avoid trees and large shrubs, which will outgrow the bed within a few years.

Crop Rotation

Grow the same crop in the same bed year after year and you build up soil pests and diseases, and deplete specific nutrients. Crop rotation avoids this. The traditional rotation is four groups, moved around four beds each year.

The four year rotation

• Year 1, Bed A: Legumes (peas, beans). Fix nitrogen in the soil.
• Year 1, Bed B: Brassicas (cabbage, broccoli). Need nitrogen, follow legumes.
• Year 1, Bed C: Roots (carrots, parsnips, onions). Need firm soil, low nitrogen.
• Year 1, Bed D: Potatoes and cucurbits (courgettes, pumpkins). Need rich soil.

Each year, move each group to the next bed. So in Year 2, Bed A has brassicas, Bed B has roots, Bed C has potatoes, Bed D has legumes. After 4 years, each group is back where it started, but the soil has had a rest from each crop.

Maintaining Raised Beds

Annual top up

Each spring, top up the bed with 5cm of compost or well rotted manure. The soil level in a raised bed drops over the year as the organic matter decomposes. Just spread the compost on top and let the worms work it in. See the RHS guidance on raised beds for more detail.

Mulching

Mulch the bed in late winter with compost or leaf mould to suppress weeds and retain moisture. Avoid bark mulch on vegetable beds as it ties up nitrogen. See our guide to mulching for general principles.

Weeding

Raised beds need less weeding than flat ground because the soil is loose and weeds pull out easily. Hand weed regularly, removing weeds when they are small. Avoid hoeing, which damages the soil structure.

Watering

Raised beds dry out faster than flat ground because they are above soil level. Water deeply once a week in dry spells, more often for shallow rooted crops such as salads. See our summer tidy checklist for watering reminders.

Wood treatment

Timber raised beds need no treatment if you used pressure treated timber. Untreated timber should be treated with a wood preservative every 2 to 3 years, avoiding the inside of the bed where the soil is.

Replacing timber

Eventually the timber will rot. Pressure treated timber lasts 8 to 15 years, scaffold boards 10 to 15 years. When a board rots, replace it. The soil holds its shape, so you can usually replace one board at a time without disturbing the bed.

Raised Bed Problems

Drying out

Raised beds dry out faster than flat ground. Mulch heavily, water deeply, and consider installing a simple drip irrigation system. Group beds together so they shade each other's sides.

Slugs and snails

Raised beds can be a slug paradise, particularly the gaps between the boards. Keep the area around the beds clear of debris, and trap slugs with beer traps. See our hosta profile for slug control methods.

Cat damage

Cats love to use freshly dug raised beds as a toilet. Cover bare soil with netting or twigs until the plants are established. A mulch of sharp gravel also deters them.

Soil depletion

If you grow the same crop year after year, the soil becomes depleted of specific nutrients and builds up specific pests. Rotate crops annually and top up with compost each spring.

Timber rot

Even pressure treated timber rots eventually, particularly where it touches the soil. Lift the bed every 5 years and check the bottom of the boards. Replace rotted boards promptly to avoid losing the soil.

Cost of Building Raised Beds

For a 1.2 by 2.4 metre bed, 20cm high, the cost is:

• Pressure treated timber: 30 to 45 pounds
• Corner posts and screws: 10 pounds
• Soil mix (topsoil, compost, sand): 30 to 50 pounds
• Cardboard and mulch: free or 10 pounds
• Total: 70 to 115 pounds per bed

For four beds, allowing for a four year rotation, the total cost is 280 to 460 pounds. This is a one time investment: the beds last 10 years or more, and the only ongoing cost is the annual compost top up.

Designing a Raised Bed Garden

For a productive vegetable garden, plan for at least four raised beds to allow crop rotation. A common layout is four beds, each 1.2 by 2.4 metres, arranged in a square with 60cm paths between. This fits in a 5 by 5 metre area and produces enough vegetables for a small family.

Make the paths between the beds wide enough for a wheelbarrow, at least 60cm. Wider paths, 90cm, are more comfortable. Cover the paths with weed suppressing membrane and gravel or wood chip to keep them clean and weed free.

Consider the aspect. In the UK, a south facing bed gets the most sun. Taller crops such as runner beans and brassicas should be on the north side of the beds, so they do not shade shorter crops. See our low maintenance plants guide for related design ideas.

Frequently Asked Questions

How deep should a raised bed be?

For most vegetables, 20cm is enough. For root crops such as carrots and parsnips, 30cm is better. For deep root crops and potatoes, 40cm. Anything deeper than 40cm is for ergonomic reasons, not for the plants.

Do I need to line a raised bed?

Only if you are concerned about chemicals leaching from pressure treated timber, or if you want to extend the life of the timber. Use heavy duty polythene and leave the bottom open for drainage. Most gardeners do not bother lining.

Can I put a raised bed on concrete?

Yes, but you need a deeper bed, at least 30cm, and you need to add drainage. Lay a 5cm layer of gravel at the bottom, with drainage holes drilled in the sides of the bed just above the gravel. Do not put a solid bottom on the bed.

How long do timber raised beds last?

Pressure treated timber lasts 8 to 15 years in contact with soil. Scaffold boards last 10 to 15 years. Recycled plastic lasts 25 years or more. The bottom of the board rots first, where it touches the soil. Lifting the bed and replacing rotted boards extends the life significantly.

What is the best soil mix for raised beds?

60 percent topsoil, 30 percent compost, 10 percent sharp sand. This mix is free draining but moisture retentive, and rich enough for vegetables. Avoid using only compost, which is too rich and lacks soil structure. Avoid using only garden soil, which compacts.

Final Thoughts

Raised beds are one of the most useful features you can add to a UK garden. They improve drainage on heavy clay, warm up earlier in spring, are easier on the back, and produce more food per square metre than flat ground. A weekend's work and a hundred pounds gets you a productive bed that will last for years.

If you would like help building raised beds, sourcing materials, or setting up a vegetable garden, get in touch with our team. We work across the Chilterns and can build beds to your specification and fill them with the right soil mix.

Further Reading

• Low maintenance plants for the Chilterns
• Garden maintenance cost guide
• Soft landscaping service
• Garden maintenance service

Sources and citations

This article draws on the following sources. Specific claims are cited inline where relevant.

1. CGM field records (2024-03. Site observations from gardens across Oxfordshire, Buckinghamshire, Berkshire and Bedfordshire.
2. Royal Horticultural Society (2024). RHS Gardening Advice and Plant Finder. Available at rhs.org.uk.
3. Met Office (2024). Regional climate averages, South East England. Available at metoffice.gov.uk.
4. British Geological Survey (2024). Soil parent material data for the Chilterns and Thames Valley. Available at bgs.ac.uk.