I have grown vegetables on two adjacent allotments for the past few of years; plot ‘A’ using raised beds, plot ‘B’ using traditional methods and I can’t say that one is has produced better crops than the other. My conclusion is that it’s probably a good idea to employ both methods side by side.
Having raised beds with paths made up of wood chipping allows all year round access, particularly during the wet winter months when you want to harvest your brassicas and roots without compacting the soil by walking on it. Raised beds also allow for better crop protection since you have a wooden framework in place to anchor your netting or fleece. A further advantage is that crop rotation schemes are simpler to organise since you have permanently sited beds, which you can number and set out on a plan for yearly use. There is also the therapeutic value for those of us who like to build and construct things out of old cast off timber, or those with an orderly cast of mind who like to create permanent shapes in the landscape!
Another advantage of raised beds is when the soil is very heavy and suffers from poor drainage. It’s much easier to work on a small raised area than attempt to improve the soil conditions across the whole plot. Weeding is made easier too by having access to the bed from all sides – so long as the width of the plot is no more than 4 feet or so. Some gardeners advocate raise beds because they believe in the advantages of the ‘no digging’ policy. The idea being to build up the soil with layers of compost so that over the years you produce a rich absorbent texture which will hold moisture and plant nutrients, requiring little labour and leaving the soil undisturbed. I have an open mind on this and will wait to see the results. On the other hand, it must be said that some seeds germinate best in soil that has not been recently added to with manures or compost.
Regarding the ‘no dig’ ideal, I have found it necessary to use a fork in some of the raised beds to loosen the soil when clearing out slower growing or deeper-rooted crops. The climatic conditions in South Cambridgeshire, where I grow, are amongst the driest in the country, which will of course have a ‘hardening’ impact on the soil, so the use of mulches of composted material is important whether you cultivate on raised beds or open ground. I am sceptical of the argument that raised beds allow the soil to warm up sooner. Air temperature and sun light, I would have thought, remain the key determinants. Underground heating would help a bit, but I doubt if I could get it past the management committee!
The cost element is one problem with raised beds. To reduce the cash outlay I recycled some eight foot long 4×4 inch posts from my old garden fence, to create four of my raised beds. I positioned the posts on corner bricks to have them sitting slightly above ground level and fixed them in place with screws and metal braces. The idea being to prevent them resting heavily on damp soil and quickly rotting. Which brings me on to another point – the amount of time spent in setting out raised beds.
Perhaps the biggest disadvantage of raised beds is the loss of planting space arising from the network of paths. As much as a quarter of my plot ‘A’ is made up of paths. Quite simply, I would not have used this method of cultivation if I did not have the second plot. I should also mention that I seem to get more problems with rodents such as mice on the raised beds than the open ground of plot ‘B’. This is despite the fact I use perimeter wire mesh fencing, netting and fleece! They seem to be attracted by the layout – perhaps their tiny brains have become accustomed to associating the wooden frames with food supplies – or am I only imagining it? The perpetual battle with rabbits and mice and pheasants and pigeons gets you that way.
Also, there is something slightly sterile about growing on raised beds – dare I say it, it’s a bit too regimented. I do get more satisfaction from planting out traditionally on my plot ‘B’ where each year the space is used differently; where my squashes and pumpkins can run wild and free and my potato patch moves on a three-year rotation. I still grow plants in rows but I am attempting to break free from old habits by using blocks and squares where appropriate – in the case of celery and celeriac for example.
Going back to potatoes, it seems to me that a large open area is much better than using raised beds. I still prefer digging a trench, laying down some well-composted material and setting my spuds before raking over and heaping up. It’s old fashioned and it works.
When I compare like for like sowings between plots ‘A’ and ‘B’ of crops such as spinach, carrots, leeks and brassicas I find no difference in quality or quantity that can be put down to the intrinsic advantages of one method over the other. I imagine that this experience is common amongst fruit and vegetable growers. There are good points about using raised beds, as I have mentioned, but these benefits relate more to ‘organisational’ matters. It may be easier in some practical respects to grow on raised beds but my experience tells me the jury is still out on the key question – do they produce better harvests?
Which takes me to a final point. It’s important to have an ‘evidenced based’ approach to fruit and vegetable cultivation; to find out what works in your particular conditions and make changes based on your own successes and failures. The great thing about gardening is that given some thought, over time, you become your own expert.