Plants work with microbes symbiotically to receive the food transported through the media. Roots absorb nutrients through cell walls and small gaps (intercellular spaces) in the root network. Microbes and mycorrhizal fungi make homes on the roots and provide the plant with nutrients in easily useable forms, thereby acting as root extensions. This microbiome is known as the rhizosphere and plays an integral role in the plant’s health and growth. Nitrobacter are crucial in fixing nitrogen in root areas, making it easily available for the plants. In exchange, the plant returns exudates (sugars) created during photosynthesis to the microbes as food.
Aquaponics excels at growing leafy greens and herbs because of the high nitrogen environment created by the fish and two teams of nitrifying bacteria. Nitrogen, in the form of nitrates (NO3-), promotes vegetative growth, which looks like dark green leaves and strong stems. By absorbing nitrate from the system, the plants effectively clean the water enough to return directly to the fish.
Just like the fish, your plants have basic needs and it is your duty to give your plants the conditions under which they can thrive. Plants breathe carbon dioxide like we breathe oxygen. They absorb water through the air and through their roots. Their leaves “eat” light and their roots absorb nutrients to grow big and strong. They require adequate space to grow to their fullest potential and a little bit of wind to give them exercise. Yes, plants need exercise too! Plants are also very responsive to temperature on their leaves and on their roots.
Plants breathe oxygen with their cells and respire carbon dioxide back out into the air. Their leaves and roots are covered in pores that absorb gas from the air and soil. I know what you are thinking, “I thought plants provided us with oxygen?” You are correct. There are two processes that plants use to exchange gases:  cellular respiration, a processes that uses oxygen and food like sugars to produce energy like adenosine triphosphate (ATP) and waste like carbon dioxide,  photosynthesis, see light below for more info.
Plants absorb water through their roots and through their leaves. Media moisture and air moisture (humidity) levels are both vital to plant health and should be carefully planned for any crop you want to grow. These levels will vary depending on your crops.
Light is a primary factor in healthy plant growth and plays a major role in promoting vegetative and fruit production. Light is measured in PAR value, which stands for photosynthetically active radiation. It measures the total available light energy that the plants can use. Photosynthesis is the process by which plants use light energy and carbon dioxide to produce oxygen and sugar. The plants use some of the sugar for energy and trade the rest to the microbes in exchange for nutrients like nitrate. Light comes in many spectrums or “temperatures”. Each temperature has unique impacts on plants and dictates a different process in the plants daily routine. Control over light spectrum gives the grower a whole new level of optimization in the plant’s growth cycle.
Plants require a wide variety of nutrients beyond the sugars produced by photosynthesis. On a basic level, every green plant needs nutrients from two general categories: macronutrients and micronutrients. The six macronutrients that plants need in relatively large quantities are nitrogen, potassium, phosphorus, calcium, sulfur, and magnesium. There are seven micronutrients that are needed by plants in trace amounts. These are iron, copper, zinc, boron, molybdenum, manganese, and chloride.
Plants have two main zones that need protection, the root zone and the plant canopy. The root zone in aquaponics depends upon the method of hydroponic growing you choose. This is dictated by the plants you chose. Some plants do well in deep water culture while others do better in flood and drain trays with grow media. The plant canopy should be protected from unintentional destruction or harsh elements. The plants should not be so protected as to totally limit plant movement or growth space. Plants need exercise too and a gentle circulating breeze provides them with the perfect amount of stress to grow strong.
Every plant has a preferred temperature range. It is important to study your preferred crops carefully and tailor your system to their needs. Make sure to match them to your chosen fish! The water temperature is just as crucial as the air. Temperature is an important cue for the plant, dictating when in the “season” it is. Temperatures at the root zone and the plant canopy are important indicators as to when plants start to put out flowers and fruit.
Plants consume nutrients from the water to grow and expel waste in the form of oxygen and sugar. Oxygen is respirated out of the leaves. The sugar is released as root exudate, which is the fancy way of saying the roots release waste like sugar into the soil. This waste is consumed by bacteria in exchange for valuable nutrients. By doing this, the plants remove nitrate (NO3-) and leave clean water (H2O).
Much like your fish, your plant crops have been playing an integral role in managing your aquaponics system. Now, after a lifetime of providing you with filtration for your fish, your plants grant you their final gift, an abundance of crops for harvest.
What type of crops do you want to grow?
Aquaponics can grow an incredible diversity of plants. The key is to tailor your system hardware and living ecosystem to meet the plant’s specific needs. Below is a list of just some of the plants we have personally grown to great effect in our aquaponics systems. This list is very similar to what you’ll see from most aquaponics growers.
We start with vegetative plants like leafy greens and herbs because that is what aquaponics excels at. The high nitrogen environment created by the fish and microbes drives abundant vegetative growth.
Fruiting plants require a specific variety of different nutrients beyond just nitrogen. If you want to grow fruit crops, ensure your microbial ecosystem is well established and that the specific macro and micronutrients your plant needs are abundant in your system.
Finally, we list some ornamental plants we have grown. These are perfect for decorating your home, imagine never having to water your houseplants again! There is also a grand opportunity for commercial farmers to quickly grow and sell ornamental plants using aquaponics.
- Lettuce (Red/Green Oak Leaf Salanova, Red/Green Butter Leaf Salanova, Mesclun Mix)
- Head Lettuce (Romaine)
- Asian Greens (Bok Choi)
- Exotic Greens (Malabar Spinach, Mizuna)
- Genovese Basil
- Boxwood Basil
- Mint (any variety)
Fruiting / Flowering
Bushy - Does Not Require Support
- Bush/Determinate Tomatoes
- Bush Beans
- Jalapenos & other Hot Peppers
- Sweet/Bell Peppers
Vining - Requires Support
- Cordon/Indeterminate Tomatoes
- Yellow Squash
- Green Squash
- Pole Beans
- House plants like Spider Plants and Bamboo
- Small Bushes including Large Bushy Herbs
Small Trees / Saplings
- Green Tea
- Banana Tree (Rob Torcellini of Bigelow Brook Farm)
Again, this is a list of plants we have grown ourselves, or have seen many times with our own eyes, like Rob’s banana tree. This is what has worked for us, maybe it will work for you too. If you try these plants or any others that didn't make our list, let us know how it went with the blue chat icon in the bottom right corner of the screen!
Make sure to do your homework here! Don’t skimp. Study the plants you want to grow. Use google to understand their favored conditions. Make sure that they match the needs of the fish you want to grow. Feel free to return to the Fish section and revisit your decision based on your crop choice.
Note for Commercial Growers:
Batch Cropping vs. Cut and Come Again vs. Conveyer Cropping
Every plant has a different growth cycle, leading to different times from seed to harvest. However, when you are beholden to production quotas to make good on your contracts, you must understand exactly how much produce your farm will provide you with and how often it can provide it.
That is why it is so vital to understand your planting schedule. There are three main ways to harvest commercially: batch, cut and come again, and conveyer cropping.
Batch cropping is when you harvest your whole production all at once, then start over with seedlings. This method is not recommended for aquaponics because it will greatly disrupt the ecology of the system to suddenly lose all the filtration from the plants. Additionally, it is not great for commercial producers who want a more consistent line of production to meet weekly orders.
Cut and come again refers to any crop that you can harvest from multiple times over a period of time without having to replant it. Examples include kale, basil, sage, and oregano. Benefits of this include less labor associated with seeding and transplanting. There are diminishing returns to most cut and come again crops because the new growth eventually becomes slower and slower to come back. At this point, it is prudent to fully harvest the crop and replace it with a new one. This type of diminishing return and subsequent harvest can cause hiccups in production and must be accounted for in your planting schedule.
Conveyer cropping refers to the continual activities of seeding, transplanting, and harvesting every week. By harvesting just a portion of the total plant load each week, you can maintain balance in the aquaponic ecosystem, maintain consistent but low labor costs, and ensure weekly production for your clients. This works best for crops that can only be harvested once, like most leafy greens.
Every plant lends itself to either cut and come again or conveyer cropping and each style can be combined effectively in your system, depending on which plants you chose.
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