Aquaculture cropping: less is more

Aquaponics is simply amazing technology, and an aquaponics system is thoroughly enjoyable to operate, so it is unsurprising that we easily get carried away when growing crops using this methodology. There is also the commercial imperative to produce as much as possible from our systems, and for both reasons we find at times that we plant, or permit, too much growth in our systems.

This can be as a outcome of planting the seedlings too close to each other, which results in the plants competing for light and growing vegetatively without much fruit set. It could be as a consequence of not pruning old growth regularly or completely removing plants once they pass their stage of maximum output of harvestable material (either leaves or fruit). Vine crops tend to remain in the beds for several months and there is a temptation with them to plant the replacement seedling at the base of the old vine during the last few weeks of harvesting from the mature plant. As there is no need for crop rotation in aquaponics, this may seem like a good way of gaining growth time in the beds, but in reality is not a sustainable plan. It could even just be a poor choice of variety i.e. using a variety that is not well suited to growth in aquaponics. The classic example here is an extremely vigorous variety of golden cherry tomato which we tried (twice!) and found to be such a productive grower that it smothered everything around it (both times) with the result that pruning was nearly impossible and effective spraying with (organic)

pesticides was rendered impossible, resulting in a pest population explosion (again – both times!). Goldilocks, a golden cherry tomato variety that grows so rampantly in aquaponics that it smoothers neighbouring plants and blocks the pathway, even when being pruned heavily The trouble with permitting over- growth is that it reduces the open spaces between plants, restricting air flow, permitting fungal infections and pests to establish. Compounding this, pest sprays are less effective, bearing in mind that virtually all the sprays we use in aquaponics are gentle, contact treatments with no residual action. Under these conditions plants fail to thrive, and such over growth therefore actually has a detrimental impact on productivity. The solution therefore is to remove the old plants before planting seedlings, only plant varieties well suited to aquaponics, prune frequently and plant at the correct spacing. When we follow these basic rules we can continue to enjoy farming in aquaponics. This truly is a case of less is more. By: Leslie Ter Morshuizen, Aquaponics Africa.