First of all: Welcome to the beginning of a new series with us. We’ve just finished the build of a small, but diverse Aquaponic system in our garden and I’m excited to share this new knowledge with you. This post is going to be more of the theory behind these two systems, and the next posts will get more into the specifics of what I’ve done in the garden and how that’s working out so far.
So first up, we need to define what these two types of gardening are:
Hydroponics is a method of growing plants without soil. This seems counterintuitive, but soil does two main things for us, and we can recreate these two things without soil. 1. It provides a place for nutrients and oxygen to be absorbed into the plants. and 2. It provides support for the plant to remain in place.
It turns out that if we construct a specific type of system, we can provide both of those things to a plant and get better results than with traditional gardening. In a hydroponic system, water is in a “closed-loop” system, which means its pumped through and recycled over and over again. This dramatically reduced the amount of water needed over the lifespan of the plants. Liquid nutrients are mixed into the water at regular intervals to provide sustenance for the plants. We can also grow much more in a given footprint of land, as we can grow vertically.
Aquaponics takes this approach one step further. Instead of adding nutrients to the system, we stock live fish in the water reservoir., which is a process known as “aquaculture” or “raising fish in a controlled environment. The fish are fed, and their waste is broken down by the natural cycling of ammonia, ammonium, nitrate, and nitrites in the water, and feeds the plants. This is akin to what you’d find in a natural pond and is a symbiotic relationship. The fish waste feeds the plants, and the plants remove impurities from the water and keep it clean.
Naturally occurring nitrifying bacteria obtain their energy by oxidizing ammonia and nitrite, and turn it into plant available nitrates. Without these bacteria, the water would soon become toxic to the fish, and the plants wouldn’t be able to absorb the raw nutrients in the form of ammonia.
Ammonia is excreted through the respiratory system of the fish, and the ammonia and waste rich water is taken up into the grow beds, which provide a home for the nitrifying bacteria to flourish in. The ammonia is processed by the first group of bacteria and becomes nitrites, and the nitrates are processed by a second group of bacteria into nitrates. (NO3)
Ammonia and nitrites are poisonous to fish and not useful to plant, but nitrates are not poisonous and are what is absorbed by roots.
Similarities between the systems:
One of the most attractive reasons for pursuing these methods of gardening is how much it extends the regular growing season, especially when housed indoors. Small, recirculating systems are very commonly seen inside houses near a sunny window, or in a garage with grow lights. I’ve even seen complex, larger systems fill a greenhouse and grow food year round outside.
Weeds: gardening in these methods practically eliminate the need to deal with weeds. Less time is spent weeding and fewer applications of chemicals to combat them create a more pleasant growing season. Time can be spent on the more enjoyable aspects of gardening, like feeding the fish and harvesting plants.
Water Consumption: an aquaponics system uses about 10% of the water normally consumed with soil based gardening. This makes is particularly friendly to the environment and a more elegant solution where water is limited or produced from a well.
Plants grow faster: on average, plants from 30-40% faster than they do in soil. The nutrient solution is typically more observed in hydroponics than it would be in soil, and much more easily managed, and plants receive optimal levels of all nutrients.
Differences between the systems:
With hydroponics, all of the nutrients are measured and supplied by you. It requires careful monitoring of the levels dissolved in the water and additional feeding every couple of weeks throughout the grow season. Because of this, hydroponic systems tend to remain very sterile and do not require a lot of extra growing material to support the plants. Grow beds can be smaller and shallower. Hydroponic systems are not self sustaining ecosystems. You are in charge of monitoring and supplementing all nutrients and changing them out.
With aquaponics, you need typically twice the depth of grow bed to harbor the beneficial bacteria required by the Nitrogen Cycle. Roughly 12″ of depth. You also will need additional components that filter out fish waste solids out of the system, or you will end up with a very gummy and foul smelling grow bed. A balanced aquaponic system more closely mimics nature and will self regulate a little bit more. You will be less concerned with individual nutrient levels and more concerned with the pH and health of the fish.
With the exception of the cost of fish, the costs of both systems are fairly similar. The cost scales with size and complexity. Each plant requires a certain volume of water in the system, typically a gallon or so per plant, so you need to be able to provide water reservoirs large enough to hold an appropriate amount of water for X number of plants. One very popular solution, and one I implemented and will talk about more in another post, is to use a food grade IBC plastic container. These are known as “chop and flip” hydroponic systems because you basically take the top 1/3″ of the container, cut it off, and flip it upside down. The bottom, larger container is now the water reservoir, and the top is the grow bed.
With both systems, you will need a pump and access to electricity. My system has two pumps (combined 60 watts), an air pump (24 watts), and a large 300 watt aquarium heater if necessary but not turned on all the time. Continuous power draw for me is 2 kwh/day, or 735 kwh/year, which is roughly $0.22/day or $80/year. Not bad, but you need to be aware of the continual running cost. Some folks really like to power their pumps off a small 100 watt solar system, and I’d like to get there one day (so keep your eye out for that project to come).
With aquaponics, you’ll need an air pump to oxygenate the water and fish food.
Prebuilt systems are available but can become prohibitively expensive, so pursuing DIY options dramatically reduce the overall costs.
Another large cost is the grow media itself, if you pursue media grow beds methods. Hydroton clay balls are a very popular choice because they are inert, pH stable, and have lots of porous surface area where bacteria can colonize and oxygen can proliferate and are very lightweight, but they are very expensive. Other options would include river rock pebbled, basalt from a landscape supplier, or lava rock, but these grow beds can become very heavy.
With hydroponics, you’ll need liquid nutrients, which can be expensive regimens and can get fairly complicated with the administration. I bought a liter bottle of nutrient solution for $19, and it’s a well reviewed product, but also one of the cheapest options out there. You’ll also need to occasionally flush the system (typically once a month) to remove accumulated waste nutrients and salts, and then refill and refeed.
For aquaponics, you’ll need fish and fish feed. I bought 30x 4″ channel catfish from a farm about an hour from Dallas for $1 each, so fairly inexpensive for me here. I bought 50lb bags of floating catfish feed for $12 at tractor supply and two bags of that will probably get me through their lifetime. Feed cost can be supplemented by plants like duckweed, but it’s already fairly inexpensive so I’ll be focusing my attention elsewhere.
Hydroponics are quick and easy: all you need is a couple days for the build, fill it with water and nutrients, and plant.
Aquaponics takes a bit more time as the water, typically coming from the tap, must “cycle”, which is the process of beneficial bacteria populating the system so that fish waste can be broken down. This typically takes about a month to begin, and up to 3 months to stabilize. Anyone who has ever had a new fish tank is familiar with the concept. The bacteria must colonize before fish are introduced or dangerous levels of ammonia will build up and can harm the fish.
Aquatic based growing systems require a frequent monitoring of the pH level. Plants typically favor lower pH (5.5-6), and fish favor slightly above that with optimal levels right around a neutral 7. With hydroponics, setting the level is a bit easier and can be done with occasional checks and chemical additions, but with living fish in the system, it gets a bit more complicated. Fish waste decomposing will naturally lower the pH over time, necessitating more frequent checking and buffering, which will push the pH back up. There are a lot of different methods to do that, and might warrant its own post soon, but a couple of quick methods are simply purchasing a pH buffering kit on amazon, with solutions of pH up and pH down, that can be added to the system as needed, or floating bags of oyster shells in the pond, which will naturally react with acidity and dissolve, bringing the pH back up. This is the method I am going to try, since I already have some oyster shells for chicken grit, but I still have a lot of experimenting to do here.
Both of these systems are widely used and are both worth consideration. I personally chose aquaponics because even though it requires a little more planning and setup, it’s less monitoring overall once started, and I also like the ability to harvest catfish in the fall in addition to the vegetables.
I hope this intro helps and gets you interested in trying this out! Stay tuned for upcoming posts about how to build your system, the costs involved, and the beginner mistakes that I’ve made that you can hopefully avoid!