What is a raised bed
A “raised bed” is created by adding a layer (at least a foot) of soil on top of the existing soil and using a frame to keep the soil in place. Instead of digging down into the soil, you are effectively raising the level of it by a foot. The raised bed is therefore an ingenious cheat to provide good quality, deep, fertile soil that’s perfect for planting.
Why use them
Generally speaking you need a good spade’s depth of quality top soil in order to grow decent veggies. Urban and suburban GIYers face the issues of poor soil quality in their garden, and lack of time to spend improving the soil quality. In most housing estates in Ireland the ‘soil’ was created by departing builders throwing a miserly inch-thick layer of top soil on top of the builder’s rubble – good luck growing anything nutritious in that!
Benefits of raised beds
- Typically, you don’t ever stand on the soil which means less soil compaction and therefore better drainage (although the soil will dry out quicker).
- They also tend to extend the growing season because the soil in raised beds warms up earlier than the soil around it. You can therefore start planting earlier in the season.
- The dreaded slugs tend to be less of an issue too because they face more barriers to get into the bed.
- You can build and design them to fit your space and even build them into your garden or patio furniture.
- If you have mobility issues a raised bed can make growing easier and more accessible as they require less bending and stooping.
- A raised bed is easier to maintain (weed, dig etc) than a large area of open ground.
Designing your raised beds
It really doesn’t matter – square, rectangular and triangular beds. The important thing to remember is that you are not supposed to be walking on the soil at any point, so you must be able to reach into the centre of the bed from all sides. A 4ft square (1.2m) bed is therefore considered ideal because the centre of the bed can be reached from both sides.
You can buy raised beds or make them yourself from old scaffolding planks or salvaged timber. If you are buying planks of wood to build beds, try to source un-treated timber. Generally railway sleepers are frowned upon because of the amount of toxins in them – however, if you are lucky enough to have some lying around, you can line the inside with polythene to prevent leaching of oils into the soil. More durable/permanent beds can be made using concrete blocks or brick – however, we wouldn’t advise this for the beginner because they are expensive and you might also decide afterwards that you have put them in the wrong place!
You must be able to reach the centre of the bed from the sides. A 1 metre wide bed is therefore considered ideal, (depending on the length of your arms) because the centre of the bed can be reached from both sides. But don’t push it up against a wall.
The beds should be a minimum of 25cm deep. You can go as deep as you want, even up to waist height. Deeper beds have the advantage of being easier to work at – no bending or kneeling. But they are expensive to fill with soil, drain very quickly and are therefore difficult to keep watered in summer. A false bottom in a very deep raised bed might be a bit more complicated to make, but it raises the bed to a very convenient height and cuts down considerably on the amount of soil and water needed.
Choose a sunny, sheltered, well-drained spot.
A typical argument against raised beds is their cost. In reality, you can spend as much or as little as you want. You can buy flatpack raised beds, have them made for you by a local tradesman or make them yourself from old scaffolding planks or salvaged timber (at GIY we use recycled pallet wood).
The Basic Plan to Make Raised Beds
- Measure out the lengths of wood needed, cut them to size and screw them together.
- Support from the inside using wooden pegs at each corner, then screw the planks to the pegs for support. At this point move your raised bed to its proposed location. Check you can access all the way around it and that you can reach the centre.
- Place a thick layer of wet cardboard and/or newspaper on the ground beneath to kill off grass and weeds.
- Fill with compost and top soil.
Adding the Soil
Fill the beds to within about 10cm of the top so that the sides of the bed act as a windbreak. You should aim to incorporate a good deal of compost or manure at this initial stage – a mix of about 60 per cent soil and 40 per cent compost would be ideal.
Where to get top soil from? You can buy top soil in garden centres but it will be expensive. Specialist soil mix providers like Enrich sell larger quantities (1-tonne bags). Ask at your local GIY group, gardening club, growers’ group or allotment organisation. Failing that, keep an eye on local papers, advert sites and social media for people getting rid of topsoil. But be careful who you buy from and ask to see the soil before it’s delivered. You do not want a big lorry load of subsoil that might be full of stones and weeds.
You can just leave grass growing around the beds if you want. However, gravel paths have the advantage of being weed free (black landscaping fabric called mypex goes down beneath the gravel, which allows water to drain away but prevents weeds from coming up). If you work around the beds on a wet day the grass around them quickly turns muddy – there is no such problem on gravel paths. There are lots of other approaches – brick, paving slabs, bark mulch etc. Make sure any paths you put in are wheelbarrow width (1m at least).
If rabbits, pets etc are a problem you should consider putting in a picket fence or chicken wire fence around your plot. To keep rabbits out you will need to put chicken wire to a depth of 1ft to prevent them from digging underneath it.
When to build
Autumn is a good time to put in raised beds. If you get them built in the autumn and early winter and filled with soil, you can add in some compost and manure and cover them down for the rest of the winter so that they will be bursting with nutrients and ready for planting next spring.
For more growing tips and resources visit www.giy.ie