While reading about Peak Oil I stumbled across a way of growing large amounts of food in small areas (enough to feed your family in the area of a small back yard). The system is called Aquaponics. The idea is that you have two tanks, a grow bed and a fish tank. The water from the fish tank is pumped over the grow bed, then returns to the fish tank via gravity.
Here is the design for small system from the Backyard Aquaponics site:
The fish are little fertiliser machines. They take food, and output nitrogen rich fertiliser. This gets pumped onto the grow bed where bacteria break down the fish waste into nitrogen compounds. The plants just love these compounds and grow like mad, cleaning the water at the same time. A very neat little system – you get rapid growth of plants and fish. It’s a protein/vegetable machine. With no artificial (i.e. derived from oil) fertilisers. I have seen claims of 50kg of fish and 200kg of vegetables from backyard systems over 6 months, which I figure is enough food to supplement (or feed entirely) a typical family.
Now I am pretty geeky and have never grown a thing in my life. I am much more comfortable with silicon and solder than dirt and water. However aquaponics interests me for a couple of reasons:
- If the Peak Oilers are right and transport and hence food costs increase dramatically, then knowing how to grow some of your own food could be a very useful skill to have in a few years.
- I am intrigued by the possibility of efficient food production for the developing world.
- It has the right sort of complexity to interest me, i.e. I get to mess with pumps, and dream about solar powering the whole thing. I also like the idea of the symbiotic system, lack of waste and efficient use of water.
Inputs are water, a little fish food (I understand you can grow your own worms if you want), sunlight and electricity for the pump. The electricity bit I don’t like. I would love to go solar on this, and work out exactly how much water flow I really need. In a developing world situation is it easy to imagine a hand or bike powered pump, or even in a pinch a bucket.
So I bought an aquaponics DVD and book and decided to have a go. Of course I wanted to go full-throttle on this and build a large system but wifely approval was not forthcoming so I scrounged a small, skunk-works type project for about $75:
- small 1200 litre/hr 15W pond water pump ($40). Probably too big for what I need.
- 10 goldfish ($20) (2 have gone to fishy heaven so I have 8 left).
- 1 tomato and 1 chili plant seedling ($10).
- old ornamental pond ($0).
- empty plant pot ($0).
- gravel from driveway ($0).
- fish food ($5), half gone after about 10 weeks.
To complicate matters I am a notoriously fussy eater and don’t actually like fruit and vegetables much! So I planted all the stuff I do like to make a pasta sauce: tomatos, chili, and garlic! I would have also liked to plant potatoes and onions but I am not sure if those sort of vegetables work in aquaponics systems.
My goldfish are not for eating (unless you are a neighbourhood cat), just to provide nutrients for free. Here is my system:
This is about 8 weeks after starting. The large plant on the left is the tomato and was just peeking over the top of the pot when I planted it. The pot sits on some bricks in the middle of the pond. A small pump supplies water to a plastic pipe laid on top of the pot with a bunch of holes punched in it. The water trickles down the rocks in the pot to the pond.
Here is a top view:
The pump is under the water at the bottom left, you can see the electricity cable running to it. The fish get all excited when they see me, as they think it’s lunch time. They really do recognise me BTW. It’s nice to be wanted.
Just when I thought I was getting into the groove of this gardening caper I suffered a biological warfare attack. Nope, it wasn’t Saddam, or even Osama, but some caterpillars having a party on my beloved tomato plant:
There was some low level nibbling for a few weeks then in the space of just two days half my bloody leaves were gone! It took me a while to work out the problem, but I bought some spray from the local gardening shop and after a good spray I noticed a big fat green caterpillar wriggling in the water. Apparently they can’t swim. Too bad.
I also noticed some of the little yellow tomato flowers dropping into the water. This is bad news as it’s these flowers that turn into tomatos. A bit of Googling showed that this can happen when tomatos get too much nitrogen. Now it just so happened that I had started feeding the fishies twice a day, as I had thought the now-larger plants would need more nutrients. So I have now backed off to just one feed a day and the latest crop of little flowers are staying put.
Some relatives who know something about gardening have also suggested I prune the tomato plant, this focuses growth on the tomatos rather than unnecessary branches.
Some lessons learned:
- If the pump gets blocked, you can get into big trouble quickly, e.g. my tomato plant went all droopy within hours. If you have a high stocking density of fish I understand their oxygen levels could also drop quickly which could lead to disaster.
- The pond water is crystal clear; my experience with fish ponds is they usually go quite green. So the systems seems to be cleaning the water quite nicely.
- A large scale system could be made really cheaply. The two tanks could be holes in the ground (one slightly above the other to provide gravity return) with cement or plastic lining. Fish breed for free. The rest is labour.
Aquaponics uses small amounts of water compared to regular agriculture. I use about 1-2 buckets a week (4-8l), not much compared to what I imagine would be regular watering of these plants if they were planted in soil. When you think about it, normal watering of crops is grossly inefficient. When you spray the water around you maximise it’s surface area, almost guaranteeing most of it evaporates before it can get to the plant.
You see I live in the state of South Australia, which is the driest state in the one of the driest countries in the world. We also have serious water supply problems, persistent droughts, and the climate change is making that much worse. So low water consumption is a very good thing.
It’s kinda cool to see the growth in action, little flowers turn into baby tomatoes and I have countless green chilis. The garlic plants spang from single cloves that I just pushed a few cm under the rocks, it was amazing to see little green shoots emerge a few days later! I also enjoy messing with the system every day, it gets me out of the home office and into the back yard. I would really like to build a larger system, with say 20 eating-fish, and a solar powered pump system. However my wife is afraid we won’t eat all the food it produces. Maybe a project for 2008.
I recently had to restore this blog from a backup and unfortunately lost the two comments from the original version of this post.