Posted: 29/01/2012 at 19:46
The material choice for the actual beds was 200mm x 47mm pressure treated timber, bought in 5.4m and 4.8m long lengths. 4.8m lengths were chosen as I wanted the beds to be 1.2m wide, and this length gave no wastage. 5.4 was chosen as I wanted some of the beds to be 2.7m long, so again no wastage. Once again pegs were 47mm x 47mm by 4.8m cut and pointed to 600m long lengths.
The first job was to paint them to help preserve the timber further. In hind sight this was a waste of time and money, as the paint turned out not to be UV resistant. It was fine below ground, but not above.
The bed system was constructed by first cutting the material to the chosen length and width, followed by screwing it together to form a bed shape. The bed was then aligned in position using a string line that had been off set. Steel pins were used to help keep the position of the bed, and a laser level was used to set the height. Each bed. Once I was happy with everything pegs were driven into the ground at approx 650mm centres, after having first made a hole with a steel bar. The pegs were banged in flush, screwed with 90mm screws and a back weather was then cut. I prefer to use screws over nails, as they can be adjusted, and also there is no risk of knocking pegs loose. When putting in the corner pegs, keep them approx 100mm away from the corner. There is a reason for this. I also found that whilst very long beds are lovely, a bed size of 1.8m x 1.2m seems to be the ideal.
Anyone thinking of doing a project such as this, take a look at the modular fruit cage/plant protection sizes first. It would be a shame to make your beds, then discover that protection is awkward to fit or adapt.
As the beds were being created, I also wanted to start the foot paths. A terram membrane was laid down first followed by hardcore, then compacted Fittleworth stone. Obviously anything from carpet to grass will work for pathways.
And this is the finished result.
One problem that I feel all raised/bordered beds suffer from is rot and mould! Wood treated or un treated only has a limited life span when in contact with soil. With this in mind, one thing that I would recommend is that in winter, dig the soil away from the edges of the boarding on the beds that aren't being used. That is the reason for keeping the corner pegs in by approx 100mm. It gives you space to clean right into the corners, the other reason is that 100mm gives plenty of room to erect a fruit cage.
I am afraid that I am not the person to advise on soil make up etc, but slowly, I am removing the soil from each bed area to a depth of 450mm, sieving it and mixing it with sharp sand, then putting it back. It certainly makes a massive difference to the quality of root crops.
I shall write about the irrigation system next.