Aquaponics allows for plants to be grown closer together. Unlike in soil agriculture, plants do not have to develop massive root systems in the ground to gather nutrients. The constant exposure to nutrient-rich water reduces that need, resulting in stout and more vertical root growth. This means, plants can effectively grow in closer proximity. How closely plants can grow is still up for debate,
In challenging this concept we've packed our 20-square-foot grow beds with about one hundred seeds. Yes, you read that correctly ONE HUNDRED. This worked OK, resulting in beautiful bright green waves of leafy lettuce and greens. The nutrient-requirement for these plants is fairly minimal and it likely that some seedlings eventually were choked-out by others. Afterall, we had a HUNDRED plants in a 20-square feet space. Short of handling and hand-counting the mature plants, it's difficult to know how many plants thrived out of the hundred. Best guestimate is maybe 75-90 plants - pretty incredible. Either way, in this case we really maximized that 20-square feet of real estate without major costs or problems. The only reason, I say this worked OK is that because when you have such high plant densities in a small space a small problem can rapidly multiply. Take for example your common greenhouse pest, the white fly. If quickly spotted, treated (we prefer organic methods such as white-fly predators like lacewings and ladybugs) and removed you can reduce the spread of such pests. However, if you are experimenting (which we encourage) and testing-the-limits on plant densitities, the spread can be rapid and knock-out an entire crop of lettuce (which it eventually did). We were able to enjoy multiple harvests before the white flies became a problem and learned from our planting densities experiment.
Overall, we consider super high-plant densities a break-even. We had high yields for a little while, but eventually lost our crop to the rapid spread of the white fly which then created a need for urgent pest-fighting strategies: total crop removal and ladybugs everywhere.
We've since stepped-away from our plant density experiments for the time being and are back to sowing our seeds 6-10 inches apart (depending on the plant type). Of course, this applies when we plan to harvest plants from our aquaponic system. When we plant to generate starter plants or seedlings, we sow much closer and remove plants from our system long before maturation. Check out the picture above of a small portion of our tomato starter plants that came from 20-square-feet of aquaponic grow space. We grew those starter plants, potted them, and helped to distribute thousands of these future fruit bearers to communities in partnership with schools. In total from just 20-square-feet we grew and distributed over 1200 tomato plants. Awesome, right?!
However, you choose to grow and for whatever purpose, plant density is something you can play and experiment with. From experience though, we urge you to keep the end goal in-mind, consider the plant nutrient requirements, and be wary of the potential risks if you lose a crop, because we know from experience it can happen easily and quickly.