All plants may have different nutritional requirements; for instance leafy green vegetable require more nitrates than fruiting plants. However all plants in aquaponic systems need 16 essential nutrients for maximum growth. These come in the form of macronutrients, which in addition to carbon, hydrogen, and oxygen, which are supplied by water, carbon dioxide, and atmospheric air, include nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), phosphorous (P), and sulphur (S). There are seven micronutrients necessary as well and they are chlorine (Cl), iron (Fe), magnesium (Mn), boron (B), zinc (Zn), copper (Cu), and molybdenum (Mo). These nutrients have to be balanced, as an excess of one may interfere with the uptake of another, as is the case when potassium affects the bioavailability of magnesium or calcium. Iron concentrations in aquaponic wastewater are insufficient for plant growth and therefore iron has to be supplemented to a concentration of 2 mg/L.
Many types of plants can grow successfully in aquaponic systems. The Crop Diversification Center in Brooks, Alberta has reported growing over 60 different food crops in their aquaponics trials (Nelson, 2008). Originally it was thought that only leafy green vegetable and herb crops could be grown, but it has since been proven that a wide variety of fruiting crops, beans, and flowers can be grown effectively.
Although many crops can be grown in an aquaponic system, some are more suitable than others. When choosing a crop to cultivate, the grower’s objective should be taken into account first and foremost. If the objective of the venture is to turn a profit, as it is with commercial scale systems, then crops that have a high market value and short harvesting time will be more appropriate. These include herbs such as basil, chives, cilantro, and parsley whose harvest times are between 25 and 40 days
Lettuce is the most grown crop in aquaponics due to both its short harvesting time (3-4 weeks) and high demand in western diets; because a large portion of its final mass is harvestable and edible, it is a very lucrative crop. Another reason these crops do well is because the lack of a fruiting stage keeps nutrient requirements consistent, resulting in a more reliable harvest. Other leafy green vegetable of this nature are Swiss chard, Pak Choi, Chinese cabbage, collard and watercress, which in addition to the aforementioned advantages, also experience less pest problems than fruiting plants
While fruiting crops of all kinds are successfully grown in aquaponic systems, they are mostly cultivated by hobbyists growing for consumption or by researchers. Because these plants have longer harvesting times, they are better suited to growth in areas that have a longer growing season such as the tropics where growing can be carried out all year long. Melons, tomatoes, okra, peppers and corn are all popular fruiting crops crown in aquaponic systems