We have now been running our aquaponics system for a year. It was installed as part of a PhD project emerging from Sheffield Hallam University, exploring how a lay-person would take to soil-free gardening, and capturing lessons that may prove of use if the approach is to be taken up more widely.

Last September we posted our lessons from the initial design and cycling of the aquaponics system, and here is the experience gained from using it in earnest.

  1. Temperature: we are still waiting for the live temperature monitoring system planned by the University, but temperatures in the tank got down to 5C in this uncharacteristically long, cold winter. We keep carp in our system in part due to their ability to cope in a range of temperatures, and whilst their activity seemed to slow, there was no significant problem.
  2. Temperature time-lag: the salads planted in the spring were a lot faster growing in the soil than aquaponics. Without monitoring data it is hard to specify the cause but it is likely that problems with the auto-siphon (see 8)  slower supply of feed and oxygen, and we suspect that the temperature of the water was slower to rise than that of the soil.
  3. Over-winter plants: our main problem over winter was vermin rather than temperatures. The kohlrabi were eaten in one night. But other plants thrived, and we had a supply of green leaves from Mizuna, chard and spinach plants through til Spring.
  4. Thermal mass: Another success were the tomatoes which survived 6 weeks longer than those a meter away that were planted in soil. This may be due to their later planting, but their close proximity to heat-storing thermal mass may also play a part. The mass is in the clay balls in which they are planted, the water, and the dense concrete blocks that support our growing beds – against which the tomatoes were trailed.
  5. Minerals: We share the produce grown between our five households, and concern was raised about whether they were as healthy as soil-grown plants due to a lack of minerals. This prompted some further reading but we were on the right track:
    • Maxicrop to add micronutrients in our initial cycling
    • Rocks from our carp pond helped introduce naturally-occuring bacteria
    • To this we added, after three months, composting worms which seem to be surviving well, and there is no sign of mineral deficiency in the leaves or crops.
  6. Sowing medium: some seeds have self-sown (tomatoes), and some peas and beans have successfully grown from seed scattered in the beds, but vermin were a significant problem – perhaps due to the long winter. To get round this we started seedlings off in an Ikea hydroponics kit in a conservatory, made more sustainable by using our own sheeps’ wool to form the sowing medium, instead of mineral wool.
  7. Evaporation: again, we are yet to receive the monitoring equipment but it seems more water is evaporating than we would expect, with the system requiring approximately 300 litres top-up every 2-3 weeks in growing season.
  8. Cleaning: it took a long time to select fish food and it’s not clear we made the right choice. A lot of it is either not properly digested or dissolved and so occasionally blocks the pipes or is spewed out in to the last growing bed in the system. This bed is now protected to some degree by a sieve under the inlet pipe, but we would advise others to experiment with different feeds before buying a 25kg bag! The outcome of this was that the inlet water slowed to the point it was insufficient to trigger the auto-siphons, the growing beds did not drain once flooded (unless triggered manually) and so plants were starved of oxygen for much of the day.

The plants we are now testing for the first time (for us, at least) are French beans, squash, kale and spring onions. The French beans are densely planted, and are producing many more although much smaller, finer beans than those planted in neighbouring soil; the squash and courgette are slower to take off than those planted in soil, as is the kale, so it is still early days; but it is a delight to finally grow some spring onions which have never taken off in our soil beds.

You can follow more of our food-growing ventures on Instagram.

Date posted: July 9, 2018 | Author: | No Comments »

Categories: Food

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