With the recent turn for the better in the weather, we decided it was time to head back out to Carbeth to plant and cycle our gutter system. When we opened the polytunnel door, a completely changed sight met us – everything is shooting up! Beautiful purple broccoli, a small sea of dill, and even a few lemons are making their presence known at the moment.
Carbeth Eco is a hub for sustainability innovation, and they’re testing all sorts of things from optimum wavelengths for plant growth to the soil consistency. But our main focus of the day was on continuing what we had started one cold day in January – our gutter aquaponics system.
We’re starting out with well-established seedlings so that once the system is cycled they’ll be able to absorb the nitrates out of the water for the fish, but we’ll also be starting out some new plants from seed shortly. It’s a good idea to have plants at different stages of growth so that your system maintains steady levels – if all the plants were harvested at the same time, there would be nothing to draw the nitrates out and you could have an algal bloom or a bunch of dead fish on your hands.
We got our hands on some strawberries (Alpine and ‘Cambridge Favourites’), lemon thyme, mint, and peas to start with.
In the next few weeks, as the system becomes more established, we’ll also try sprouting some lettuce from seed – it would be great to have a whole tray of multicoloured salad greens!
Because the plants came in soil, we had to carefully and thoroughly wash the roots before putting it into the system. This is to avoid transferring any unwanted bacteria that might be living in the soil, and to avoid muddying the water.
After that we just slotted the plants in where we want them – as simple as that! We might need to do some rearranging in the coming weeks, but they all have plenty of space to spread out so we’ll see. The mint will no doubt take over soon, but if it becomes too unruly, it can be taken out almost as easily as it was put in, which is one benefit of using the clay substrate.
Finally, we needed something to kick-start the cycling process. We need to build up the bacteria that will convert the ammonia left in the water by the fish into nitrite, and another that will convert the nitrite into nitrate, which can be absorbed by plants. There are several ways of doing this (in the past we’ve used ammonium chloride), but since Carbeth Eco has a trout pond teaming with all the nitro-bacteria your heart could ever desire, we decided to try seeding it naturally. A few minutes of scouting around the pond, and we were able to fish out a brick from the pond. Unconventional, perhaps, but worth a try!
The rest of the work for the moment is up to the bacteria. We added a bit of ammonium chloride for food, but we’ll need to wait for colonies of both types of bacteria to develop before fully introducing our fish. We originally planned on putting trout fingerlings in this system because the pond stocks trout, but because of the heat the polytunnel is already generating, it will be too hot for them. However, tilapia could very well be the perfect new residents for the gutter system – stay tuned!