Constructing raised bed gardens is a relatively simple task, and the rewards from using them for growing food, compared to growing food in the ground, can be phenomenal. Raised beds come in all shapes and sizes and do not necessarily have to be "contained beds" although they are by far the most popular choice and easiest to manage, and in that spirit, this article is all about 'contained beds'.
They can be as simple or as complex as you want to make them and can be placed directly onto the ground, or if like me, you are planting on a patio, then they can be constructed with their own base arrangement, as I demonstrate in the video below.
My video on how I constructed the raised beds for my garden
Materials You can use all sorts of materials in constructing raised bed gardens; wood, cylinder blocks, brick, or even stone in a dry-wall arrangement. Some people like to improvise with recycled materials.
It's down to your imagination, the location and the materials available to you to determine what you end up with. Ultimately all you are looking to do is contain some high quality soil above the ground, no deeper than about 12 inches. All other details and how you go about doing that is entirely at your discretion, although if you stick to a few other rules outlined below, they will help you to get the most from your raised bed garden.
Location Obviously you can build raised beds wherever you like, but if you want things to actually grow in it, then you will need to locate it in a productive area.
Choose a place where it will get good sunlight. Depending on which plants you intend to grow, you might get away with partial shade, but as a general rule, the shadier the area, the less growing potential. Also, with the beds being in full sun, they will tend to dry out quickly, so making sure there is easy access for watering is a must. - Also see 'Irrigation & Drainage' below.
Size When constructing raised bed gardens, size is very important. One of the major points about growing in raised beds is that the soil is high quality, light, airy and oxygenated - the perfect growing environment for plants to flourish. However, if you make your raised bed garden so big that you have to walk onto it in order to tend it, they you will be compacting the soil. Compacted soil is pretty useless for growing in, it deprives roots of oxygen and will be detrimental to your growing efforts. You could reduce your yields by as much as 50% by trying to grow in compacted soil. You might as well save your time, money and effort and grow directly in the ground if your raised beds are to be walked all over!
The four feet rule: I've borrowed a rule from the square foot gardening method here; a good size to make the beds would be two, or four feet wide, depending on whether you have access to one or both sides of the raised bed. Make it two feet wide if you can only access it from one side - that way you can reach to the back without ever needing to walk on, or lean on the soil to support your own weight, causing it to compact. If you have access to both sides of the bed, then a four feet wide bed will be fine.
Any wider than four feet and you will need to lean or tread onto the soil in order to reach the centre areas, so a good practice wherever possible is to never make your contained raised beds more than four feet wide.
Irrigation & drainage One of the drawbacks to using a raised bed garden is that they do tend to dry out quickly. Regular watering is essential, often twice a day.
Before constructing raised bed gardens, it's important to decide whether or not you want to install any kind of irrigation or sprinkler system, as many systems will be require installing during the construction phase.
Most people will choose to water manually via a watering can or a hose, it's a good way to regularly check on your plants as they grow, others will choose to add a porous hose system later on when they discover that watering your plants twice a day can be quite a tedious task! So it is worth giving some consideration time to alternative watering options before you start work on building your beds.
When constructing raised bed gardens, they must be built with good drainage, that means they are built in a way that enables excess water to drain out easily, otherwise the roots will not get enough oxygen and the plants will perform poorly.
If you are intending to build a raised garden onto permanently wet or boggy soil, then consider either adding a base to your bed, keeping it raised off the ground, or alternatively, make your raised bed sides much deeper, and add several inches of large stones and gravel at the base to form a good drainage barrier between the soil in the raised bed and the soil on the ground.
Retaining the moisture - an experiment One of the methods I hope to be experimenting with this year is the polythene sheet membrane barrier method, where you place a piece of polythene over the entire bed. When you come to add your plants, you cut a small cross in the polythene and plant so it sticks out from the sheet. The idea is that it minimises moisture loss, and also keeps the temperature of the bed higher, hopefully encouraging better growth. Quite how practical this method will be in every-day use, I will find out.
Before adding the soil... One of the things that you might not think about when constructing raised bed gardens, is whether the materials you use for the construction are likely to contaminate the soil in any way.
If your raised bed is directly on the ground, then make sure you remove any woody plants or weeds within the container walls.
Adding a weed barrier membrane would also be a good move.
Fill the bed with good quality soil. Too much clay and it will not drain well; too much sand and it will not retain water sufficiently, so go for a good middle-ground arrangement; A good mix of compost, manure and loamy topsoil would be the perfect recipe for a successful growing season.