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RAISED BEDS
The 'Bed' system of vegetable growing (Please click on drawings to enlarge image & PRINT if required) It seems one cannot pick up a vegetable gardening magazine, equipment catalogue or even watch a gardening programme on television these days without finding some reference to "raised beds". One could be forgiven for thinking that there is something magic about them which automatically ensures successful cropping. Sadly, this isn't so and I expect their popularity has more to do with the fashion for growing vegetables where the raised bed offers those with very small urban gardens a way of providing a small patch of good soil with a reasonable depth. For those with money to spend on the bed framework and imported topsoil, the raised bed offers a "quick-fix" solution. Having said this, I do not wish to imply that the 'bed' system of growing vegetables has nothing to offer those with larger vegetable plots be it part of their domestic garden or a rented allotment. However, it is my view that the advantages accrue primarily from the concept of a bed system rather than using raised beds although raised beds do bring additional advantages but at a cost. My father's allotment that he worked in the 1940s was 33' 4" wide and 100' 0" long; that was pretty much the standard for allotments in East London in those days. It was an undivided plot and he grew his vegetables in neat rows across the width of the plot. Small needs were grown in half rows or even quarter rows and access for weeding, watering and harvesting was achieved by leaving sufficient space between pairs of rows along which one could walk. The whole plot was dug over and manured every year, paths and all, and planting repeated the next year having regard to the need for not planting the same vegetables in the same place year upon year.
Wooden edging, however, does help. Paths will inevitably grass over and without fairly frequent edge trimming, the grass will persistently encroach upon the vegetable plot. When the plot is dug, the soil spills over onto the paths. Wooden edging resolves both problems [if you see them as such], and simply helps to keep things tidy, although this is not the only advantage. If you are using any form of plant protection, be it insect mesh, polythene sheet to form a cloche or small tunnel, or fleece to afford frost protection then, together with the supporting framework, the wooden edging provides an ideal fixing to which to secure the bottom edge of the protective material. It is in the provision of plant protection where a wooden edged bed system really starts to confer advantage. Wooden edging also provides a good fixing for a copper strip to help keep away slugs and if gravel paths are used, the wooden edging becomes almost essential to contain the gravel. Where there
is no intention or need to raise the level of the bed, a very small timber
section can be used but be sure to use treated material and maybe even add
an extra coat of preservative yourself.
Prices include VAT and are ex BSK, Kendal.
If it is your intention to use a bed system, do give careful thought to the width of the bed. A 4'6" wide bed will just about accommodate two rows of potatoes grown the length of the bed. With the exception of very small cabbages [eg Hispi] most brassicas need a 2'0" spacing so, once again, a 4'6" wide bed will accommodate two rows along the length of the bed. For most other plantings, [eg beans, lettuce, beetroot, onions, leeks, carrots, parsnips, kohl rabi, celeriac] it is probably better to plant short rows across the width of the bed. If you intend to use portable cloches, do make sure that the bed width will accommodate a cloche module. Cloches using horticultural glass will be a 2'0" module; most plastic cloches come in 4'0" lengths so, in both cases, the 4'6" wide bed is ideal giving enough space to fix end-closing panels. However, if you intend to use cloches, choose your product and check its size before fixing your bed width. Do not forget that watering under cloches can be time consuming if the cloches have to be removed. A 4'0" cloche module used across the bed width can be accessed using a long spout watering can by simply removing the end panels. Another good reason to limit the bed width to 4'6". So, there are a few advantages to using a narrow bed system and a few more if you fit a wooden edging. With gravel paths you can even make a trip out to your veg. plot in your carpet slippers to pull a lettuce at short notice without having to don boots and full gardening kit to do so. OK, so beds can be a good idea. But what about raised beds? Well, if your ground is not frequently waterlogged, if you have a good depth of soil, your site is not so steeply sloping that rain water erosion is a nuisance and if your are sufficiently agile to be able to stoop to tend your plants, then you have no need for raised beds. However, if any of the above issues are causing a problem for you then maybe adopting a raised bed system may help. Raised beds can lift the level of the cultivated soil above frequently waterlogged ground and so improve drainage. They can be used to terrace steeply sloping ground providing a level growing surface which isn't occasionally washed to the bottom of the slope by heavy rain. If you have very stony ground that is impossible to cultivate then raised beds provide a container for soil imported from elsewhere. And, if you have difficulty bending, a raised bed just makes life a bit easier but if you can't bend at all, then your raised bed may have to be so high that building it becomes a minor civil engineering project! If you want to raise the level of your growing surface more than 5" or 6" above the natural ground level then, unless the beds are quite small [about 4'6" x 4'6"] you will need to use heavier timber sections than would be used for a simple bed edging. This adds significantly to the cost and the fabrication process demands a little more in the way of practical skills. The need for heavier timber sections is due solely to the outward pressure exerted by the soil within the raised bed when it is significantly higher than the surrounding ground. This causes the timber bed sides to bow outwards. Even with a 2" thick timber bed side, where the length of the bed exceeds about 8 feet, some form of intermediate tie-bar will be needed to resist this bowing effect [see figure 8]. Fortunately, the materials for fitting a tie-bar are readily available locally. Before we look at the fabrication of raised beds, it's worth considering a few points associated with their use.
·
Firstly, avoid the
temptation to place a raised bed directly onto compacted ground and simply
fill it with top soil. In order to ensure good drainage it is important
to loosen the ground where the bed is to be placed. If the ground is very
stony, use a pick to do this. The deeper the ground is loosened, the
better. If the site where the raised bed is to be located is covered with
turf, strip it and stack the turfs under a black plastic sheet before
loosening the ground. The turf will produce a good topsoil for later use.
·
When constructing
raised beds it will almost certainly be easier to fabricate them as
complete "boxes" on a convenient flat working surface, carrying them to
the site and setting them into position on the already loosened ground;
filling them with the imported topsoil being the final task. · With very large beds, prefabrication raises the issue of weight. A bed size 4'6" x 12'0" x 12" deep and made with 2" thick timber will weigh well over one hundredweight. This will sensibly need two people to lift it. If you make something even bigger then it is better to prefabricate the sides and assemble the bed in situ. With these points in mind, the following sketches show a few simple constructional details for making your own raised beds from timber. I must stress that these ideas are not exclusive. Raised beds can be made from concrete blocks, logs, railway sleepers, indeed anything that will retain a depth of soil.
· Start by cutting the sides to length noting that the long side overlaps the short side. · Cut the corner blocks so that their length is the same as the width of the sides. Pre drill the short sides [as shown in figure 9] and fix the corner blocks to both ends of each short side using 8mm x 100mm hexagon headed coach screws and washers and ensuring that the side of the corner blocks are flush with the end of the short sides. Note: The corner blocks will not need to be pre drilled. · If you are working on a reasonably flat surface, the short sides with their corner blocks attached can now be stood on end with a distance between them equal to the length of the long side. · The first long side, pre drilled [as shown in figure 9] can be laid between the two short sides and fixed using 8mm x 100mm hexagon headed coach screws and washers and 6" galvanised nails making sure that the ends of the long sides are flush with the faces of the short sides. · With the two short sides and one long side now fixed together, turn the whole thing over and fix the second long side in the same way as the first. · For the tie bar, I suggest you use a length of 8mm or 10mm diameter rod and there are two ways of acquiring this. One way is to go to any local metal fabricator [eg Michael Mudd at Smarthwaite] and ask them to cut a piece of rod about 1" longer than the overall width of the bed, thread the ends for you and fit a nut and washer to both ends. Alternatively, you can buy 1 metre lengths of galvanised "studding" [threaded rod] from most builders merchants together with nuts, washers and a joining coupling. You will need the joining coupling as your bed will be wider than the maximum [1 metre] studding length. If you use studding, you will clearly need a hack saw or angle grinder to cut the rod to length. To fit the tie bar you will need to drill a hole centrally in each long side. Sliding a length of old plastic water pipe over the tie bar will afford it some protection from corrosion.
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