Pots, Potting Mix, And Seeding
Good aquaponics sprouting methods involve putting the seeds into a slit pot holding potting media. Right from the beginning, we always used 60% fine coconut fiber (coir) and 40% vermiculite for this – NEVER use anything that contains peat, soil, or other “potting mixtures”, even if it says it’s sterile, as it will bring fungi and destructive molds into your system! Wet the coconut fiber overnight in a plastic garbage can (or other appropriate container) full of water, then break into small pieces to mix more easily with the vermiculite.
(Below) A block of coco coir soaked overnight in aquaponics water before mixing with the vermiculite we use in the potting mix.
Make sure that when you work with dry vermiculite you wear a cartridge respirator (NOT a paper mask!) because vermiculite dust is classified as a carcinogen! As soon as the vermiculite is wet and mixed with the coir it is no longer a risk because no dust can escape or powder off into the air.
Be on the lookout for salty coconut fiber/coir; it is sometimes washed with saltwater during processing, but not rinsed afterwards. Once when we were having poor germination, we checked the water we were soaking the coir in and found it to taste SALTY! (that was Tim; he tastes everything!). Now, we check each new batch’s soak water; if it comes up the least bit salty, we rinse it before using it to make the potting mixture.
Put this 60/40 potting mixture in 2-inch slit pots in a plastic nursery tray that holds a lot of them for easy handling, then put the seeds on the top of the damp potting mix in the pots. Now, spread a thin layer of vermiculite only on top of the pot, covering the seed with 1/8 inch or so of vermiculite. Water the nursery trays full of pots on top of the vermiculite to make sure the seeds are nice and damp, then put the nursery tray directly into the sprouting table (we’ll cover those in a moment).
Special Note: You don’t need to use bigger slit pots than 2-inch: we’ve grown a 7-pound taro corm and a 2.87 pound turnip in 2-inch pots using this technique! We tried leeks in 3-inch pots for awhile (3-4 leeks to a pot), until we realized we weren’t getting any better production per pot, and were using more system real estate with the 3-inch pots! Well, we did use a 3-inch pot once to grow a 10-foot tall banana tree in a raft, but that was just an experiment, not commercial production!
After the plants have sprouted to about 2 inches tall in the sprouting table, and before their roots start coming out the holes in the bottoms of the sprouting trays, you transfer the pots, little plants and all, to your rafts for growing out to their final harvestable size. Don’t let them get much bigger than this before you transfer them to the rafts, for if they have lots of roots coming out through the holes in the bottoms of the sprouting trays, pulling the pot out will rip off these roots, causing transplant shock in the plant and resulting in poor growth.
You can’t beat these little plants over the head: if it’s wintertime and your sprouting tables are too cold for optimum germination (or for germination at all), you may need a heated germination area (70-80 degrees F), plus heated sprouting tables to give your seeds the best chance to germinate and grow. If it’s summertime and your sprouting tables are too hot, you may want to add some light Aluminet or other infrared-reflective shade cloth over the tables (try 20% to 30% shade cloth, any more shade may make the sprouts attenuate (lengthen towards the light).
Can’t find coco coir? We’ve heard of people successfully using shredded dried banana leaves and plant stems for potting mix. Try whatever you can find locally that is soft, holds water, and won’t poison your plants or fish. Try it in a small aquaponics system first!