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.
Note; 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.
Construction;
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;
Untreated softwood will have a shorter life, although alternatives such as oak and western red cedar will last for many years.
Timber treated with a wood preservative, should be lined with pvc sheeting (old compost bags make a cheap effective liner) to reduce the risk of the preservative leaching into the soil.
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 plants' 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; prior to filling, fork over and loosen the existing soil, 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.