What would be the best way to plant a sprouting seed in aquaponics? Mesh pot with rockwool or stonewool? Or just clay pebbles surround the seedling?

Answer from Chris Bond: I take it to mean that you have a seed that has already germinated and is ready for transplant into your system versus successfully sprouting a seed that is directly sown into the media. The “easy” answer is that if you have a healthy seedling and a clean system, you should be able to plant your sprout into any of the media that you have mentioned.

I personally prefer rockwool for starting out plants for hydroponics (both for direct seeding and transplanting), because I like the support the plant gets before it has fully rooted out and can support itself. Many growers have luck directly sowing into clay pebbles, but unless you do this routinely or until you have enough practice setting the transplants in without damaging the roots, I would suggest wrapping a small wad of paper towel or other absorbent material, even a wad of cotton, to help hold the seedling in place until it roots into its new home.

Don’t be alarmed if there is a delay in noting any growth for even a few weeks while your transplant adapts to its new home, so long as everything else is in balance (light, temperature, pH, and electrical conductivity). If you are, however, looking for quicker turnarounds, such as for commercial production, direct sowing will usually reduce the time from seed to harvest. If you are just starting out or a hobby grower, starting with transplants are a good way to get your “feet wet” or rather your plants’ roots wet.

Answer from Dr. Lynette Morgan: The best way to sow a seed into an aquaponic system would depend largely on the type of seed you want to germinate.

Smaller seeds such as tomatoes, capsicum, and many other vegetables would be best supported in the mesh post with stonewool (rockwool) or a similar moisture retentive medium, which will ensure there is enough water and oxygen around the seed and young plant for early development. These types of growing mediums also provide the support required for smaller seeds as they can easily become dislodged when substrates with a larger particle size are used, particularly if this is an ebb and flow type of aquaponic system.

Larger seeds (especially those which are pre soaked before sowing) can be started in smaller grade clay pebbles, however, since clay pebbles don’t retain a lot of moisture and are very free draining, particular attention needs to be paid to the frequency of irrigation in the aquaponic system to ensure the seed or young plant never dries out during the critical establishment stage. Clay pebbles do have the advantage of being very highly aerated, so oxygen should not be limiting to the seed or seedling, however, moisture levels can be restrictive in the upper levels of the root zone where seeds are usually placed for germination. In these types of systems, salt can also accumulate on the surface of clay pebbles, which may restrict germination of some species.

As a compromise it is possible to use one of the small propagation cubes of stonewool (one inch across) to hold the seed and place this cube directly down into the surface of the clay pebbles — the young plant will rapidly grow roots through the cube into the clay pebbles without the requirement for a mesh pot and a large amount of stonewool.