Forming raised beds, can allow the gardener to improve their soil resulting in he/she being able to grow a greater range of plants at a more convenient level.
This is particularly useful for invalided gardeners who find they are unable to bend down to tend beds at ground level.
Another advantage is, as well as adding height and interest through changes in levels, raised beds can also incorporate design elements such as a water feature, or seating.
Their greatest advantage apart from reducing the need to bend down is the ability to produce growing conditions suited to what the gardener wants to grow e.g.
Heavy soils can be made much lighter and better drained.
Alkaline or acid soil pH’s can quite easily be reversed.
Soils can be made to warm up earlier in spring, resulting in earlier plantings and or flowering.
The raised beds discussed here are somewhat different from the contained beds that are often referred to as raised beds.
Contained beds, are where some form of kerb is laid to contain soil in the bed and prevent it encroaching on to the access footpaths.
Quite often these kerbs are made of building blocks / bricks or scaffolding boards and are usually around 150-225mmm (6"-9") high.
As with the raised beds the soil contained within the boundaries can be be improved or replaced as necessary, but they will not necessarily help the wheelchair bound gardener apart from keeping the access footpaths clear.
The choice of materials required to construct raised beds are many.
For relative cheapness, one can adopt a DIY approach and use re-cycled materials or have more expensive stone/brick walls built by a builder.
A few things to remember are;
Oak and western red cedar will last for many years but are quite expensive.
Untreated softwood is cheaper but sadly has a shorter life which in the long term could make this approach more expensive.
In the end the choice is with the you!
Timber treated with a wood preservative, should be lined with pvc sheeting to reduce the risk of the preservative leaching into the soil.(old compost bags make a cheap effective liner)
Similarly, if the bed is to be used for ericaceous (lime-hating) plants, it is best to seal the mortar or line the sides of the bed with pvc to separate the lime mortar from the plant roots.
Form drainage holes at the base of walls to prevent a build up of water forming in what now is effectively a tank.
When forming raised beds it is worth taking a long term view of their eventual use. e.g.
Do you want them to fit in with an overall layout plan for the garden?
Do you want them to be contoured, terraced or just some rectangular bed to grow vegetables in?
Once you have decided this here are a few guidelines to suit a few of those mentioned.
Vegetable beds are best situated with the longitudinal axis running north to south.
This allows the sun from the east and west to shine across the bed.
Beds should be roughly 1000-1200mm (3’-4’) wide to ensure the centre of the bed is easily accessible from either side of the bed.
The height should be approximately 600mm (24”) high.
These widths/heights should be made to suit the reach or particular ability / disability of the user.
Access should also be considered e.g.
Minimum width for barrow access should be 1000mm (39”)wide, and 1200mm (48”) for wheelchair access.
Paths should be constructed of some material that will be suited to the prevailing weather conditions, i.e non-slip in winter, free draining when wet, solid enough to avoid wheelchairs sinking into it, and relatively maintenance free.
Filling the beds will be governed to a large extent as to what is going to be grown in them, e.g. Vegetables, flowers or shrubs that require soil pH’s +/- of neutral(7)
Prior to filling, fork over and loosen the existing soil in the base of the bed, then add sufficient soil to fill the bed to within 150-200 mm (6”-8”) from the top.
Top off with a good quality soil mixed with copious amounts of organic matter.
For other subjects, fill the beds as described above but design the top layer to suit ericaceous or non-ericaceous plants as required.
Once the bed is filled, allow the soil to settle naturally for at least two weeks before planting.
Top up the beds after any settlement has taken place and before planting!