The idea behind this technique is to create a separate area in the top of the root zone where you can boost growth by adding fertilizer (organic, of course!) to the top roots of the plant in a way that doesn’t drain into the water for the aquaponic system and affect the fish. Here is how it works:
1) First, find a round plastic pot that is about 12” deep, and make sure that it has plenty of holes in the bottom for drainage.
2) Then fill that pot 2/3 way with the media from your aquaponic grow bed.
3) Top with a layer of fabric that will allow the plant’s roots to grow through, but will prevent the soil that you are about to add to the top of the pot from working its way down into the grow media layer. We used burlap.
4) Now, fill the rest of the pot with an excellent potting soil. We used a mixture of potting soil, worm castings, and coconut fiber (coir).
5) Figure out how much liquid the soil layer can absorb before draining into the grow media below. Cut that amount by 30%, and write it down. This is the amount of fertilizer solution you can safely add while simultaneously keeping your fish safe.
6) Plant your plant in the soil mixture.
7) Sink the planted pot into your grow bed so that the media in the pot is entirely submerged into the media in the grow bed.
8) Water the plant every few days with the amount of liquid you recorded in step 5 above so that the soil layer stays moist. We used water from the fish tank, and added Pure Blend Grow formula once a week until we saw flowers, then switched to Pure Blend Bloom.
This is an especially fantastic technique for your heavy feeding and fruiting plants. We grew two tomato plants side-by-side in the same grow bed: one in a Dual Root Zone (DRZ) pot and one directly in the media. The plant in the media did fine; BUT the plant in the DRZ grew significantly larger, faster, and put on much more fruit.