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At Norfolk School of Gardening, we have been raised bed converts for a while now and although they are definitely becoming more popular, we are not sure everyone knows just why they are such a brilliant way to grow your favourite plants.
What’s so great about raised beds?
Well, one of the best things is that you can transform your garden within a day. Go from a paved or lawn area to a fully planted raised beds in just a few hours, with no digging required. Seriously. You don’t need to worry about digging up a compacted lawn, you can leave the turf where it is. In fact you can even place your raised bed on a patio, fill it up with compost (plenty of it, well firmed) and get planting. But it doesn’t stop there. There are many benefits to growing in raised beds, and this includes being able to match the growing medium to the plant: for example, if you want to grow acid loving plants like rhododendrons or azaleas you can fill the bed with ericaceous compost. They can also be more accessible for anyone with mobility problems than a traditional bed. Indeed you can build them to the right height for you, with space between for a wheelchair as well as a wheelbarrow.
There are other advantages to raised beds too. The soil warms up faster in the spring which makes it possible to grow vegetables earlier in the year, and flowers will often get going sooner too. When there is a cold snap or the cabbage white butterflies start to lay eggs on your brassicas, raised beds are easy to cover with fleece or a net. There is something satisfyingly orderly about growing vegetables in a few raised beds, with tidy rows of salad or root vegetables and some frames for climbing beans and squash. Raised beds should always be narrow enough for you to harvest crops from the middle (roughly 4ft maximum) – and to be able to remove weeds without have to stretch too far.
As you fill the raised bed with the growing medium of your choice you are creating the ideal environment for your plant roots. In comparison to most traditional beds that means you will have better drainage as the soil will not be compacted, and the roots will find it easier to absorb both water and nutrients.
You can grow pretty much anything in your raised bed. Vegetables are the most common choices but what about flowers for cutting, a herb garden, some soft fruit or even some small trees? All of these are possible if the bed is deep enough for the roots of your chosen plants and if the compost is right for them.
Choosing your raised beds
Raised beds can be made out of many materials. They can be very fancy and take a few weeks to build, they can arrive flat packed and be assembled within an hour or if you are a DIY whizz you can start from scratch and get creative. Here are some of the most popular materials:
Wooden Boards or Railway Sleepers
Perhaps the cheapest and most common is wooden boards or railway sleepers, and it is relatively easy to make beds with some treated timber and screws, with or without a kit. However, do bear in mind that even treated wood does rot and is unlikely to last more than five years, and a lot less if you are using recycled boards. It is very frustrating when the edges collapse midway through the growing season, and a pain to have to replace them.
Brick or Stone
It is possible to create raised beds to your exact specification with brick or stone walls, using materials which may match other walls in your garden or home to make them even more aestheticaly pleasing. These will last a long time but for most people, this is a more costly and time-consuming option.
Most metal raised beds are made from galvanised steel for durability. Metal raised beds can come in a wide range of designs and finishes to fit in with the design of your garden. Galvanised steel isn't your only choice though, aluminium raised beds are growing in popularity. They are lightweight and, like timber raised beds, they can be placed directly on the ground without the need for footings. The Rhino Raised Beds are a good example of high quality aluminium raised beds which can be finished in the same colour as your greenhouse. The kit is well designed and easy to assemble.
How big and how many?
There are a couple of guidelines on size we would recommend: first, don’t go too wide – you want to reach the middle easily for weeding, pruning and harvesting; and second, don’t make it too long – or you'll be tempted to walk across it, compacting the soil and damaging plants. Other than that, it is down to you.
How high do you want the beds? Ideally beds should be at least 40cm deep, especially if they are built on paving or compacted soil. But you may want much deeper raised beds if you want to grow plants with deep roots, or to avoid bending down too much whilst gardening. If you buy a kit, you may want to get two, or even three tiers instead of one.
How many beds do you want? Are you going for instant impact with neat rows of lettuce, beans and sweet peas stretching into the distance (in several raised beds) or do you just want to have a couple of beds near the back door for herbs and salad? Or you might want to start with a couple and see how you get on. As long as you have the space you can always add more, and you could choose a variety of shapes, sizes and heights to contribute to the overall design of your garden.