Buying young plants with their first few leaves already growing is the easiest way to stock the rafts in an aquaponics system. The plants grow rapidly, need a lot less specialized care and attention, and reduce losses during the fragile seedling stage. However, most commercial operations can’t turn a healthy profit when buying transplants in bulk. Direct seeding may require learning a few new skills, but it’s worth the effort for most aquaponics operators in exchange for the savings that contribute to higher profit margins.

Seeds only cost a small fraction of started plants, but you’ll only get a portion of them to grow into successful crops. Direct seeding is tricky for aquaponics for a few reasons. First, most of the media used in deep water culture have large particle sizes that don’t hold seeds at the right depth for sprouting. Second, you must water the rafts until the seeds sprout and the seedlings manage to grow roots deep enough to reach the supply from the troughs. Finally, seedlings often die in response to the same nutrient levels that help them grow once they’re well rooted. Transplanting is generally the best option, whether you use nursery trays to start the seeds yourself or purchase stock from a supplier.

The Transplanting Process

Transplanting requires a delicate touch, which can be frustrating when you’re trying to install hundreds or thousands of individual plants. However, you’ll soon get the hang of handling the plants delicately while working rapidly and efficiently. Don’t plant the rafts while they’re in the troughs. Pick up each raft and bring it to a table or pair of sawhorses so you can work quickly to fill each net pot without stooping and bending down. The process for transplanting seedlings into a deep water culture raft system is:

• Remove the seedling from its pot or cell. If the seedling was started in a soilless media that is different from the material used in the net pots, rinse it off gently by dipping the roots into a tub of clean water.
• Apply rooting compound by dipping the roots in a solution of it if you’re using difficult plants that tend to respond badly to transplanting. Lettuce and other leafy greens can fall into this category if you are planting them very early because the shock can kill off their delicate roots. Make sure the rooting hormone is approved for use on edible plants unless you are strictly growing ornamentals.
• Make a deep enough hole in the medium inside the net pot to accommodate all of the plant’s roots without bending them back up or crowding them. Wait to transplant crops until they have enough root length to reach the water level in the trough. This may be much longer than crops would wait to be planted in the ground.
• Gently press the growing medium around the stem or base of the plant to anchor it in plant. Taller transplants will likely need stakes and other supports to keep them from leaning over and either losing root contact with the water supply or snapping off at the stem. Once the plants begin to grow, you should be able to remove these supports unless you’re growing tall and vining plants like tomatoes and beans.

Transplanted seedlings tend to droop and wilt from the stress of this transition, and this is even more likely when taking plants from a soilless medium based on peat moss to a more granular material like hydroton. The plants should recover within a day or two. If they do not recover during this period, they will likely need replacement.