A raised bed is a garden bed built up above the surrounding ground, usually held in by timber, brick, stone or metal, and filled with soil. It is one of the most popular ways to grow vegetables and flowers, and for good reason: the soil warms up earlier in spring, drains better, is easier to work without bending or stepping on it, and can be filled with good soil even where the ground underneath is poor. But raised beds are not right for every garden, they cost money and effort to build and fill, and a badly built bed is worse than no bed at all. This guide explains how to build one, what to fill it with, when it is worth it, and how to grow in it.
The core idea is simple: instead of improving the soil you have, you bring in the soil you want, in a bed you can reach from the sides without ever walking on it. That means the soil stays loose and uncompacted, roots grow well, and you can work the bed from a path without bending double. It is a system that suits vegetables especially well, because vegetables need loose, rich, well-drained soil and regular attention, and a raised bed gives them all three.
When raised beds are worth it — and when they are not
Raised beds are worth it when your soil is poor, heavy clay, very sandy, full of rubble, or contaminated; when drainage is bad and beds sit wet in winter; when you want to garden without bending, for example with a bad back or in a wheelchair, because a bed can be built to a comfortable height; and when you want a neat, defined growing area that is easy to plan and rotate. They are also worth it on a slope, where a level bed holds soil and water that would otherwise run off, and in a small garden, where a bed makes the most of the space.
They are not worth it when your soil is already good, loose and well drained — in that case, growing in the ground is cheaper and just as productive. They are not worth it if you cannot afford to fill them properly: a bed filled with poor soil is worse than the ground it sits on. They dry out faster than ground-level beds, so in a hot, dry garden they need more watering, and they freeze harder in winter. And they are a permanent structure: once built and filled, a raised bed is hard to move. If you are unsure whether raised beds suit your soil and climate, check your local extension service for advice.
Building a raised bed
1. Choose the site. Pick a sunny spot — most vegetables need at least six hours of direct sun a day — that is level, close to a water supply, and easy to reach with a wheelbarrow. Avoid a spot under a large tree, where roots will invade the bed and shade will limit growth, and avoid a frost pocket at the bottom of a slope.
2. Choose the size. A bed 1.2 metres wide is the standard, because you can reach the middle from either side without stepping on it. Length is up to you, but 2 to 3 metres is manageable. Height depends on your needs: 15 to 20 cm is enough to improve drainage and define the bed, 30 cm is good for most vegetables, and 45 to 60 cm or more suits gardeners who want to work without bending. Higher beds need stronger sides and much more soil to fill, so do not build higher than you need.
3. Choose the material. Untreated timber is the most common choice: it is cheap, easy to work, and looks natural, but it rots in a few years. Hardwood, brick, stone and metal last longer but cost more. Do not use old railway sleepers or treated timber that may have been treated with chemicals you do not want near food — if you use treated timber, check that it is safe for food growing. Line the inside of a timber bed with a breathable membrane if you like, to slow rotting, but do not line the bottom, because water needs to drain out.
4. Prepare the ground. Clear weeds, remove turf, and loosen the ground underneath with a fork, so roots can grow down into it and water can drain. Do not lay plastic or weed fabric on the bottom: it stops drainage and stops worms getting in. A layer of cardboard on the ground will suppress weeds and rot away, which is the same principle as no-dig gardening.
5. Build and fill. Assemble the sides, check they are level, and stake them if they are tall. Fill the bed as described below, water it well, and let it settle for a few days before planting, topping up if it sinks. Leave a path between beds wide enough for a wheelbarrow, and mulch the paths so they do not become weedy and muddy.
Depth and soil mix
Depth matters: most vegetables need at least 20 to 30 cm of good soil to grow well, and root crops such as carrots and parsnips need deeper soil — 30 to 45 cm — to grow straight. A shallow bed on top of good ground is fine, because roots will grow down into the ground below. A shallow bed on top of concrete, rubble or compacted ground is not fine, because the roots have nowhere to go. If your bed sits on hard ground, build it deeper.
The soil mix is the most important decision. A good raised bed mix is roughly equal parts topsoil, compost and a drainage material such as coarse grit or perlite, though the exact mix depends on what you have available and what you grow. Our raised bed soil mix guide gives a detailed recipe, and the raised bed soil calculator works out how much soil you need for a bed of any size. Do not fill a bed with pure compost: it is too rich, holds too much water, and shrinks as it breaks down, so the bed sinks. Do not fill it with pure topsoil either: it compacts and needs the compost to feed it. Mix them, water well, and let the bed settle before planting. The soil volume calculator is useful if you are filling several beds or large containers as well.
Growing in raised beds
Raised beds warm up earlier in spring than the ground, so you can sow and plant a little earlier, and they drain better, so they are workable sooner after rain. That is a real advantage, but it also means they dry out faster in summer, so water more often and mulch the surface to hold moisture. Our winter mulching guide covers mulch for beds, and the watering calculator gives a starting point. Rotate crops from year to year, so the same family does not grow in the same bed — raised beds make rotation easy, because the beds are defined and you can plan them on paper. Our square foot gardening guide pairs well with raised beds, because a raised bed is the natural home for a square-foot grid.
Plant closely but not too closely: raised beds reward intensive planting, but overcrowded plants compete for light, water and food, and disease spreads fast in still, damp air. Use the plant spacing calculator to work out how many plants fit. Feed the bed each year with a layer of compost, because the soil in a bed is used hard and its food runs down. In winter, mulch empty beds or sow a cover crop, so rain does not wash nutrients away. Our winter soil preparation guide covers winter bed care.
Pros and cons of raised beds
The advantages are better drainage, earlier warming, no compaction because you never walk on the bed, easier working height, good soil even where the ground is poor, and neat, plannable beds. The disadvantages are cost, the work of building and filling, faster drying in summer, harder freezing in winter, and the fact that a bed is permanent. A raised bed is an investment, and it should be built well, filled well, and used every year — a raised bed that sits empty is a waste of money and effort.
Common mistakes
The most common mistake is building a bed too wide to reach the middle without stepping on it, which compacts the soil you built the bed to protect. The second is filling it with pure compost or pure topsoil instead of a mix. The third is building it too shallow for root crops on hard ground. The fourth is using treated timber that is not safe for food growing. The fifth is lining the bottom with plastic, which stops drainage and keeps worms out. The sixth is forgetting that raised beds dry out faster, so they need more watering and mulching in summer. And the seventh is not rotating crops, so disease builds up in the bed. If you are unsure about materials or mix for your area, check your local extension service for advice.
Frequently asked questions
How deep should a raised bed be?
At least 20 to 30 cm of good soil for most vegetables, and 30 to 45 cm for root crops such as carrots and parsnips. A shallow bed on good ground is fine because roots grow down into it, but a bed on concrete or compacted ground needs to be deeper.
What is the best soil mix for a raised bed?
Roughly equal parts topsoil, compost and a drainage material such as coarse grit or perlite. Do not use pure compost, which shrinks and holds too much water, or pure topsoil, which compacts. See our raised bed soil mix guide for a detailed recipe.
Are raised beds better than growing in the ground?
They are better where the soil is poor, drainage is bad, or you want to garden without bending. Where the soil is already good, loose and well drained, growing in the ground is cheaper and just as productive. Raised beds also dry out faster and freeze harder in winter.
How often should I water a raised bed?
More often than a ground-level bed, because raised beds drain faster and dry out faster. Water thoroughly, mulch the surface to hold moisture, and check the soil with a finger before watering. In winter, water sparingly.
Do I need to line a raised bed?
You can line the sides with a breathable membrane to slow timber rotting, but do not line the bottom — water needs to drain out and worms need to get in. A layer of cardboard on the ground underneath will suppress weeds and rot away.