Transition Culture

13 Mar 2006

Top Five Things to Do With Oil Barrels When There’s No More Oil To Fill Them – #5. Make a Floating ‘Grow Raft’.

In an interview with Paul McCartney (which you can hear here) , he talks about the song ‘Yesterday’ (one of my least favourite Beatles songs…). He said he woke up one day with this song in his head, and couldn’t think where he had heard it, and went around asking his friends what this song was. He’d play it to them and they would all tell him they hadn’t heard it before. After a while he realised he must have made it up, but still wondered if one day the person who wrote the original would get in touch (now there’s an idea for making a few quid…). In putting together this, the last in the Top Five Things To Do With Oil Barrels series, I want to offer an idea which, likewise, I am sure is not mine, but which, try as I might, I am unable to find where it came from.

Perhaps I have had the only truly great original idea of my life, or, more likely, you are all about to bombard me with weblinks and books to tell me its origins. I thought it came from John and Nancy Todds book “From Eco-Cities to Living Machines”, but I have scoured it and can’t find any reference in there. No matter, here it is anyway… . How about growing food on specially constructed rafts? They could be constructed like floating mattresses, kept buoyant by oil drums, and then built up in layers of organic material much in the same way that we construct mulch beds. Starting with coarser ‘green’ matter like nettles, comfrey, whatever, and then creating layers like we do when we make compost heaps, 6 in of nitrogen rich materials, like grass cuttings, clippings of leafy plants and so on, and 6 in of ‘brown’ or carbon rich materials, like straw, shredded paper, dry bracken, that kind of thing, and so on in the sequence until the required height has been reached. The top few inches would compost. One good description of how to build beds like this is in Patricia Lanza’s Lasagna Gardening books.

The beauty of growing on a raft is that you would never need to water it, as the plants could self feed from the water below. Naturally you would only be able to do this in a relatively unpolluted water body, but for fertiliser, you could mimic the approach used in the Chinese dyke/pond aquaculture systems, where you dredge out the silt from the bottom of the pond/lake whatever, and put it on top of the beds. In China they have turned this into an incredibly intricate form of agriculture, where the pond is, in effect, used as a large compost heap, organic matter being ‘fed’ to the ponds in order to produce this nutrient rich silt, as well as the ideal conditions for the several species of carp the ponds are stacked with.

Our growing rafts would be immune to the problems of slug predation, and, being ‘free-floating’,would be immune to the invasion of couch grass and the like. Whenever we need to work on them we could just haul them in, weed and plant them, and then send them back out again. It could be an especially useful strategy in urban areas, on docksides. There could be a number of these rafts floating in the harbour, and then on market day, they get hauled in, harvested, and the produce sold. They could be very funky and interesting to look at, and would generate a lot of interest in the harbour. They could even be designed by an artist and called an ‘art installation’.

The closest thing I have seen attempted is at Ragmans Lane Farm, where Matt Dunwell made chinampas, (small spurs of land jutting out into a lake), the idea being that he would grow food on them, but that the roots of the plants would go down below water level and water themselves. The idea is set out in Bill Mollison’s Permaculture – a Designers Manual. What happened was that the water levels of the lake went down in the summer, leaving the plants high and dry. He felt this could have been got round by having a sacrificial ‘feeder’ pond above it. In the end they planted them with willows, which thrive there. Growing on a raft could get round this. These days it is seen quite regularly in ponds to have something floating around with rye straw in to stop the pond developing algae on the surface. It isn’t a great leap forward to say seeing as we already have a bale of straw floating around in the pond, we might as well put a bit of compost ontop of the bale and grow some food on it… .

So there you go, possibly a daft idea, probably someone else’s already, possibly a very useful tool in certain situations. I’d love to hear your thoughts, or ideally if you’ve actually been doing it for years and can pass on any experience as to the practicality or otherwise of the idea. Clearly it is no substitute for growing on soil in a garden, but it could have its place….

*Reference: The picture of Chinese aquaculture comes for the fantastic, but out of print “Integrated agriculture-aquaculture in South China – the dike pond system of the Zhujiang Delta”, by Kenneth Ruddle and Gongfu Zhong. Cambridge University Press 1988*.