Raised Bed Construction, Size & Material:
There is a lot of different views on the construction of Raised Beds for vegetables, but there is simply a few golden rules which should be followed.
Size:
They can be as long as you want, that is entirely down to you, whatever the physical restraints of your garden and wallet are.
Your Raised Bed must be no wider than you can physically work and maintain without having to climb onto them, so as a golden rule here will be that they should be no wider than what you can reach in from the outside to plant and harvest your crops, and that will be between 4ft and 5ft wide. No wider as all you will do is make working them more difficult, and if you can only access them from one side only, then they must be no more than 2ft 6" to 3ft wide.
Your vegetable beds should be made as deep as whatever you intend to grow requires. So if hoping for super carrots and parsnips from a 4" deep bed, then you had better think again.
Construction timber from the Builders Merchant is usually 9" wide, so this would make a 9" deep Raised Bed which is pretty standard and quite a useful depth, but you could go for 12" or more if you have the facilities to cut the wood and join it together. Or you could go deeper but is there any need? Most root vegetables would be quite happy and grow nicely in soil of 9" to 12".
BUT A VERY IMPORTANT POINT TO REMEMBER!......Your finished vegetable Beds are going to have to be filled with your soil, and the bigger and deeper the raised bed obviously the more soil they require, unless you have this soil and hours upon hours and lots of muscle to fill these Raised Beds, it is pointless making too many and too large a Raised Bed. So work out how many, and at whatever size you require and then work out how much they are going to cost to build and how much soil they are going to require.
  
The Ultimate Tool For A Raised Beds System Is The Chillington Canterbury Fork Hoe,
Which Allows You To Reach In And Turn The Soil With Minimum Effort .
Raised Bed Construction Material:
A Raised Bed system in gardens has been used for many many years. For garden plants and flowers the construction material is of no real concern, but your Raised Beds are going to be used to grow your food and once of the reason for growing your own food is so that you will know exactly what has gone into them and what you are putting inside you, so the construction material of your Raised Bed must not leach out chemicals into the soil which can be absorbed by your vegetables.
Raised Bed construction materials can go from wood, aluminium, block, brick, stone or whatever anybody has to hand and also what they are capable of building themselves, but people have been known to build their Raised Beds out of old railway sleepers and these railway sleepers are old for a reason, they were impregnated with chemicals which stopped insects and natural substances from decomposing them. One of the chemicals used was creosote based which apparently now is supposed to be highly toxic and maybe carcinogenic, so not a great material to use around your vegetable beds!
You can also buy treated timber, some of this treated timber has been treated with chemicals which are designed to kill insects and other life forms. You have to ask yourself if these chemicals on the timber leached into the soil and were absorbed by my vegetables, would those vegetables be the healthy food I am trying to grow? It can be difficult to find out exactly what timber may have been treated with but there are treatments called "CCA's". This treatment could be made up of Copper, Chromium and Arsenic, called "Chromated copper arsenate" which are just the things you probably wouldn't want inside your vegetables or indeed inside you, but how can you find out exactly what has been used in your supplied treated timber treatment, ask yourself...... Is it worth the risk? Some timber suppliers say they now use alternatives to CCA's and claim that their products are safe around food. Hopefully all timber treatment businesses have now adopted the safer method of treating timber.
You are going to all this trouble and expense to grow healthy food and right from the first stage you could be growing vegetables and fruit in a way which may be not so great?
So would you be better using untreated timber?, this would not last as long but at least those nagging thoughts would no longer concern you, but a general rule is if something has been designed to kill something then if I or my family ingested it would it do us any good?
One way around this problem is to line the treated timber with thick plastic like builders damp course plastic wherever the timber is likely to be in contact with your soil. This way you can rest assured knowing that your vegetable roots aren't sucking up anything that could be leaching out of your timber. But until someone does tests on this system we will never know if the chemicals which make up your builders plastic are leeching out into the soil and being absorbed by your vegetables roots, after all this plastic was designed for laying under concrete not growing vegetables, so perhaps the only fail safe way is to use natural untreated timber and replace your beds every couple of years.
Another natural way to make your timber last longer is use a hardwood like "oak". You can now buy untreated sawn to size oak planks for your system which will last years longer than softwoods available like white and red deal.
The other materials available are obviously going to be more expensive or and more time consuming to make. If you were to make your Raised Beds out of block, brick or even stone, these would be a more permanent feature and hopefully there is no chemicals to worry about but may be more cost effective in the long term.
Aluminium Raised Beds are a recent addition but obviously expense is going to affect the outcome of what you decide.
Making Your Raised Beds From Timber, Block, Brick, Or Stone:
There really is nothing more simple. Just cut your timber to length and screw or nail the ends together to make a square or rectangle or any shape you require. Then place on the ground where you want to position your raised beds and in each corner, knock a short stake into the ground and again midway along the longest part of your raised beds so this are level with the top of your timber and screw or nail your timber to these stakes. This will stop your timber from bulging out along the longest sides and give extra strength to the corners to stop the soon to be inserted soil from weakening the joints. If you require deeper raised beds then just use longer stakes and screw or nail on your extra planks to suit. You can line the inside of the timber with suitable plastic (builders dampcourse) to protect the timber against the wet soil.
If making out of block, brick or stone simply mark out on the ground and position your blocks/bricks/stone to form the shape and height you require. If they are to be permanent then you may want to add some kind of foundations, otherwise removing top soil and building from the compacted solid sub soil would be suitable for a dry type construction (no mortar) with concrete blocks up to a height of 9" - 12". It would be best to lay your blocks flat so that the walls of the raised beds are at least 9" thick to give them strength as they will not be bound together with mortar. With brick or stone, then you will really have no choice to put some kind of foundations down otherwise it just will not be strong enough. This type of raised bed will need no lining with plastic and will last forever.
When finished just fill with soil allowing extra as the soil will settle quite a bit after a few weeks. If you intend to add pipe work or other equipment to your raised beds, then it is best to think about this before adding your soil. This also applies to any drainage and protective plastic you may want to insert.
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