Polytunnel for aquaponics

Polytunnel for aquaponics

For year-round Aquaponics in a cold-climate like the UK, we’re going to need some sort of enclosure to keep the system from freezing through the winter. We don’t want to have to use any heating unless we absolutely have to, as it’ll quickly make the system uneconomic to run. So the question is . . . do we go for a greenhouse or polytunnel?

We’ve never used either before. Visually you’d have to go for a greenhouse, but pound-for-pound you get a bigger enclosure with a polytunnel, and on our budget that’s probably a strong factor.

The negatives?

The plastic covering for a polytunnel is relatively easy to tear, lets in less light than glass and it deteriorates so it lets in less light each year. It typically has a lifespan of 5-7 years. Replacing it typically costs only 20% of the price of a new polytunnel, so it probably still ends up cheaper than a greenhouse.

Some polytunnels have very low, or no, eaves. This limits their useful width for an aquaponic system with growbeds on stands.

Aluminium greenhouse frames conduct heat too well – reducing the insulation effect of the greenhouse.

Standard greenhouse glass is thin, and breaks into lots of small shards – very dangerous around our littlies – so we’d have to go for the significantly more expensive toughened glass.

What size is best? I’m thinking there’s not much point going wider than 3m – a one metre wide central aisle, with 1m-wide growbeds on either side. Any wider than that and I’ll have trouble reaching across the growbeds. A wide door will be essential, for moving large tanks and growbeds in and out, and door needs to be central, not offset. If we’re going for a polytunnel we”l need one with good straight sides, not one with a continuous curve. 

There are some interesting claims made for polytunnels:

Because a polytunnel encloses a larger volume of air than a greenhouse, a polytunnel stays warmer longer, providing a frost free environment for a greater proportion of the year. For an even longer growing season, bubble insulation can be used

UV blocking polythene which has all the advantages of our standard film but also blocks ultra violet light. The major advantage of this is for organic growers because it reduces Mildew, Botrytis and insect attack as insects only see in ultra violet

Having looked at the prices, we can get  good-size polytunnel for £19 per useful sqm, but I’ve struggled to find a greenhouse for much less than £127 per useful sqm. So a polytunnel it is!