Raised garden beds are exactly what their name promises – they are beds in which you can plant vegetables where the planting medium has been raised higher than the surrounding land. Raised beds have many benefits for the permaculture gardener. They prevent the soil becoming compacted, which in turn helps with water drainage and soil aeration. The containment of the soil by the raised bed also helps to prevent erosion by wind and rain, while the improved structure of the soil means that it is typically slightly warmer than the surrounding earth, meaning you can usually plant in raised beds earlier in the season. Having such well-structured and healthy soil also means that raised beds can typically support more individual plants that ground-level beds, so making them amenable to the permaculture principle of maximizing yield wherever possible. And it must not be forgotten that raising your garden beds makes tended, maintaining and harvesting from them, easier on the gardener, involving less bending. Thus, they are particularly valuable for older gardeners or those with restricted mobility.
You can purchase pre-fabricated raised garden beds, but they are fairly easy to construct yourself, and they can easily be made from recycled materials.
You can place your raised garden bed on any surface. If placing on soil, you will need to do less work, as you will leave the bottom open for the plant roots to penetrate the soil. However, you can also install it on grass or even concrete, as you can add layers of mulch material at the bottom to contain the growing medium. As with your normal garden beds used for cultivating food crops, you will want to position your raised beds so that they get several hours of full sun each day – to help the plants set fruit – and protected from string winds that could damage the plants or erode the soil.
The size of your raised bed is likely to depend upon the materials you are able to salvage to construct it. However, it is worth remembering that, given that the garden bed will predominantly, if not entirely, be given over to plants that produce an edible yield, you want to make sure that you can reach all parts of the bed for harvesting your crops. A width of four feet is a good general rule to enable you to reach all parts of the bed, and the length can be as long as you need for your planting design. In terms of height, just remember that the higher you build your beds, the more growing medium will be needed to fill them, and tall beds can experience a lot of pressure from the material contained within, so you may need to reinforce the walls of your raised bed if building it over around two feet.
Recycled lumber is ideal for making a raised garden bed. You can buy timber, but it is a lot more expensive and much less ‘green’. Cedar is a good choice if you can source it, as it is naturally rot resistant. Whichever lumber you source, make sure that it is untreated and not painted so you are not introducing chemicals or heavy metals into your permaculture plot. You will need boards for each of the four sides of your bed, extra ones if you want to add more height, and some stakes for each of the four corners to attach the side boards to.
Construct your bed in the location where it will sit; this is a lot easier than building it elsewhere and having to move it. Screw or nail the wall boards to the four corner stakes. It is also a good idea, if you have the extra lumber, to add stakes at the middle point of the outside walls, to strengthen them. If you have long beds, add a stake every four feet or so, to help the bed contain the material within.
If your bed is over grass or concrete, add a thick layer of newspaper or cardboard, with the edges of the sheets overlapping so no gaps are left. Water this layer well before proceeding. This layer will keep weeds suppressed if on grass, and provide a base level of nutrients for the raised bed. If siting over earth, make sure the area is clear of weeds before filling (you can also add the cardboard layer, but leaving the bar earth available will encourage deep root growth). Fill the bed with good quality topsoil. Augment the soil with lots of organic matter, such as compost, composted manure, grass cuttings and leaf litter. You might also want to round your growing medium, piling it higher in the middle so it slopes to the edges, rather than having a flat bed. Rounding the soil increases the surface area, allowing you to grow more plants in the space.
Once your raised garden bed is filled, it is a good idea to plant it as soon as possible. Nature hates bare earth, and weed species will quickly colonize any. And at the very least bare earth is prone to erosion by wind and rain. Plant seedlings rather than seeds for the same reason. Use planting guilds and interplanting to maximize the specimens that can be fitted into the bed, and so to maximize yield. You can also use planting to ameliorate conditions that you bed may experience due to its location. So, for instance, you can plant taller crops on the side that receives the most wind or, if in a very hot location, in a position that affords shade to smaller, more fragile plants. Water the seedlings well when they are first planted in the bed. If your plants require it, feel free to mulch the raised bed, although you are unlikely to need mulch for moisture retention, as the soil in the bed is adapted to do so. However, as with normal beds keep an eye on the dampness of the soil, and if it becomes too dry, water well.