Sunday, November 28, 2010

Raised Beds - How To Lift Your Food Growing Yields

When I started growing vegetables, one of the first jobs I got stuck into was to build some raised beds in my back garden. A raised bed is essentially any structure or format which takes the soil up off ground level. A raised bed or a series of them is a basic yet profitable arrangement if you want to grow your own.

There are a number of benefits to be had in growing with raised beds. First off, in a back garden setting, they look good, particularly if you still have some herbaceous borders, flowers and shrubs and haven't turned the whole lot over to food growing.

Raised beds made of rustic timber, stones, blocks or even poured concrete can add some architectural design to a vegetable garden which can often look chaotic. While this isn't a problem in an allotment setting, the beds will allow you to grow food in your garden without ruining its structural aesthetics.

The second factor is that the soil climate in a raised bed environment is contained and therefore it's far easier to control. If, for example, you're growing acid loving plants like blueberries and cranberries and your soil is neutral or alkaline, you'll find that even despite dosing them with ericaceous compost, they'll experience problems as the main body of the soil around them continues to change the ph back to neutral or alkaline.

Plot 34's three year old Waterer of Everything (WOE) attending to the salads in one of our raised beds

Isolated in a raised bed however, the soil can be maintained steadily at any level of ph or consistency that your plants require.

Raised beds drain far better than ground level beds and will warm up quicker than their terrestrial counterparts, thus allowing you an earlier start to the growing season.

From a practical point of view, a raised bed is far easier to work on given that you have to do far less bending down.

You can build a containment comprised of simple planks, railway sleepers, stones, bricks or even corrugated sheeting or plastic. Some people just heap the earth up without any containing medium although this can be messy in the long run.

Planks are perhaps the easiest to work with

I used log roll for my first raised bed. This is a series of one and a half foot logs split in two and then linked together via double lacings of durable wire. This stuff has the advantage of being flexible like a linked chain, allowing you to create any shape you want. A kidney shape suited the curving beds in my garden (Her Outdoors says it's a heart shape but it's a kidney).

Herbs, salads and a miniature coronet apple tree in our log roll raised bed
 After creating the shape of the bed, I pegged the log roll into place using stakes hammered into the ground on at intervals on the outside to hold the shape into place. I then lined the inside with durable plastic sheeting all along the ground and then up to the lip of the containing boundary. This is designed to keep out pests who might burrow in as well as to help contain the moisture in the bed. Because I didn't want it to fill in the rain like a paddling pool, I made strategically located drainage holes all around the base with a garden fork.

Then I filled it in with a mixture of top soil, compost, agricultural sand (for friability and drainage) and  mature manure. Don't fill a raised bed exclusively with compost from a garden centre or you'll quickly find yourself with a dried-out nutrition starved mass in which nothing will grow. 

To the right, raised beds constructed from random rocks and stones
My log roll arrangement proved ideal for mixed salads as the slugs and snails didn't relish the prospect of scaling the rough chippy surface of the log roll.

A raised bed needs to laid out in a suitable size and shape. The ideal is one which allows you to reach every part of the surface area without standing in it - you don't want to have to walk across the soil as it causes it to compact and hinders your plants.

You'll also want to select the right location.Every part of the raised bed will need from six to eight hours of full sun each day to provide enough light for viable crop growth.

Some people recommend you only use wood that hasn't been treated with chemicals. I don't see why we shouldn't recyle scrap wood like railway sleepers which has already been treated. They last longer, and a plastic sheet skin between them and the soil prevents toxics like creosote leaching into it. Reusing them prevents them ending up in a landfill anyways.

If you like you can go all the way and build two or three foot high poured concrete beds which will last forever, can be painted in pleasing colours and used double as garden seating. In Havana, Cuba, which has perhaps the world's most developed urban farming culture, a combination of cheap corrugated sheeting holds the beds in place in larger communal areas while poured concrete is used where food growing is a full time fixture.

Concrete raised beds at an urban farm in Havana
Some people even like to build high rise raised beds in undulating layers and "steps" which can also look great in the garden, particularly in a bright corner where the highest level is set to the back.

If you're thinking of installing raised beds, don't go out and buy the expensive kits from garden centres. These could see you paying E80 for an installation the size of a kitchen table and which includes nothing more than four simple planks which slot or screw together.

If you can't salvage the wood, stones or sheeting you need, go to a lumber merchants and buy scrap timber or else to a builder's yard and purchase concrete blocks and cement. You don't need to pay through the nose to raise your food growing game.

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