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!
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Hi guys,
Thank you for all the information you are sharing!
I plan on using little rockwool cubes specially designed for hydroponics.
The brand name is Grodan.
Any thoughts?
Best regards,
Jens Larsson
Hi Jens,
Friendly Aquaponics has used the 60% coir and 40% vermiculite mix since the beginning and there really isn’t a product that can touch its affordability and function.
A little known fact is that rockwool cubes are not ready to use right out of the bag. They naturally have a high pH, which will mess up your system if directly added. You will have to prep them and keep a very close eye on your system using a pH meter so it doesn’t get too high and kill your fish. The coir/ vermiculite mix is pH neutral, so you wouldn’t have that problem.
You also have to take into account what your going to do with those cubes after your done growing in them- they can’t be reused or recycled adding cost because you have to trash them. With the coir/ vermiculite mix you can compost it or put it in your green waste bin for your city to recycle. I understand that the cubes seem like they will save you time but in the long run they really are not faster then the coir/ vermiculite mix. Plus the mix is much more cost and environmentally friendly.
Hope that helps,
Jess
Thanks Jess,
I will follow your sage advice!
– Jens
Thanks Jess! I just want to add that these cubes cost around 8 cents each; compared to our current cost for the potting mix of $0.003 (three-tenths of a cent each), using them would add around $800 per week to our expenses for the 10,000 seeds a week we normally plant.
That’s $41,600 per year; and would totally bankrupt the farm! Also, they’re not USDA Organically Certifiable, so we’d lose our organic prices, and probably only make half as much gross income.
So, they’re OK for backyard hobby growers, but put a huge financial burden on a commercial grower.
Aloha, Tim……….
WHen you mix the two together how do you stop the mixture from washing trough the nettie pots back into your system?
Once they are mixed it holds together fairly well. I fill my net cups over the tub i mixed the vermiculite and coir in so that catches anything that pushes through the slits. Then I line them up in a tray and go on through the process. By the time your seedlings are ready to be put into your system the root ball holds tight to 99% of your potting media.
Do you start your seed in the this mixture as well and then just transfer them to the system?
It gives step by step instructions in this post but yes, you use the same 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”
I have a lot of pumice still lying around. I know its not the same as perlite or vermiculite, but I wonder if I could use it instead of the vermiculite in the mix? It’s pretty fine, the largest pieces being around lentil-sized.
Hey Louisa! I would not use pumice in your aquaponics system because it is almost identical to perlite in the way it behaves when it starts to break down and you do not want that stuff floating around your system! I would use it in your potted plants or mix it into your compost when your ready to till your soil plants.
Here is the reasoning on why we don’t use perlite for aquaponics:
If you are tempted to use Perlite (because we haven’t said anything bad about it), take a handful of Perlite and throw it into a bucket of water. You’ll notice that some of it sinks, some of it floats, and some of it is almost perfectly suspended in the middle of the bucket. Now take another handfull of Perlite and grind it together between your hands; notice the abrasive, sandpaper-like dust that results?
We shudder at the thought of Perlite loose in our systems, floating through at all levels from the water surface to the bottom of the tanks, abrading our pump shafts, impellers, and seals with each pass through the pump. We shudder even more about the possibility of it going through our fish’s gills until the fish died suffering from the abrasions on its breathing surfaces. You can try it, we’ll pass.
Hi,
I have been checking online sources and see that vermiculite comes in different sizes. Does the size matter?
I believe the only “size” Vermiculite comes in is coarse or fine. I know that Perlite specifically states what the mm size is but they are not the same- you want Vermiculite for your mix. Honestly I have never seen them label the 20lb bags one way or the other. Do you have a link to a specific product that you are thinking of purchasing?