The benefits of growing in raised beds includes ease of soil preparation, ease of crop maintenance, ability of modify your soil, added pest control possibilities and a neat and organised way to grow your own.
If you are considering using raised beds then there are a number of factors to consider.
Height of your raised beds
Really this comes down to what you want to grow. Herbs, salads, brassica, strawberries and legume crops only require 6 to 12 inches of root zone to grow well. Deeper crops such as carrots, onions, garlic, leeks require a depth of 12 to 18 inches to grow well. Potatoes will require the deepest beds and will require earthing up so not really suited to growing in raised beds unless you sow your potatoes into the base of an empty raised bed and fill the bed with soil over the summer as you earth up, but that sounds like more work than it is worth.
Size of your raised beds
The surface area of your raised beds will depend on your own preferences. I would recommend having 4 to 6 raised beds. This will allow you the rotate your vegetable crops each year with one rotation type per raised bed.
Raised beds have the advantage of being small and manageable in size. This allows you to divide your work load and allows you take on smaller tasks at one time. Ideally your beds should be around 900mm wide. The length of your beds is really up to you and determined by how much space you have and what you want to grow
Altering your raised bed’s soil
Smaller beds allows for easier altering of its soil. For example to raised the pH (make less acidic) of a raised bed 5m² you will need to add 500mg of lime if your beds are any larger you will require more lime. To Make your soil light and free draining you will require a ½ tone of horticultural grit for a 5m² bed.
Location of the raised bed
For best results locate your raised beds in full sun. Therefore avoid positioning on the north side of large buildings, hedgerows or trees. Ideally place paths between your beds allowing for a neat set up which will in turn reduce pests and diseases on your beds.
Anything and everything can be used to make raised beds. Plastic, brick and wood all work well and so long as they are clean and not contaminated by chemical, creasot or other then they are safe to use for growing vegetables.
Soil in your raised beds
If you have a good quality garden soil you can use it. Good garden soil will have both good drainage, fertility and water retention. Good garden soil should be easy to work and not stick to your boots when wet. When adding garden soil to raised beds mix old and new potting compost through the soil. Also add a layer of farm yard manure (4 inches) to the surface of the beds and work it down into the soil.