How To Grow Watercress In Aquaponics

Aquaponics merges two systems with fantastic results for the majority of plants. All you need to do is create the right habitat for your chosen fish and then a separate plant area. The two are connected via a pump allowing the water to circulate.

The fish waste provides the food for your plants which clean the water for the fish. All you need to do is feed the fish, monitor the setup and perhaps test the water from time to time.

Watercress is an excellent choice for your aquaponic system. It is relatively easy to grow and will provide a great introduction to the world of aquaponics.

Simply follow this guide and know how to grow watercress in aquaponics in no time; perhaps selling it for a small profit.

Choosing The Fish In Relation To Your Grow Beds

The first thing you need to do is chose the size of your planting area and the size of your fish tank. These two items are actually connected.

As a general guide you should be looking at 1 fish per every 5 gallons of water. To help you calculate the number of fish you need it may be easier to start with the amount of growing space you have. It is best to have one pound of fish for every square feet of plants.

If your growing area is going to be 2ft by 4ft then you’ll have 8 square feet and need 8 pounds of fish. Once you know which fish you wish to buy you’ll be able to work out how many that is but you must base the number of fish on their adult weight even if you are purchasing baby fish.

For 8 square feet of growing room you should be looking at between 40 and 80 gallons of water.

Create Your Tank

Now that you have figured out the size of your system you can make your fish tank. It will need to have the usual ingredients to ensure the fish are happy.

You’ll then need to add a pump that can take the fish water through to your second tank; the growing bed. Of course, the water also needs to flow back to the fish tank.

Ideally your pump should be capable of moving the entire volume of your fish tank in just 15 minutes.

You’ll also need to add an aerator to the tank to ensure enough oxygen is always present.

Build The Right Growing Media

Watercress are designed to grow in water! This means that you will be best to choose a system such as the floating raft to maximize the growth of your water cress.

This s actually very simple to do at home with materials you probably already have.

  • Start with a standard plastic fruit tray; the type that has a grid structure on the bottom and sides. You’ll need to remove any labels and clean the tray thoroughly; you don’t want to introduce the wrong bacteria to your system.
  • Next you’ll need to find or cut 2 pieces of polystyrene. They need to be roughly the same length as the tray and approximately 1 inch thick.
  • Tie one piece of polystyrene to each side of the tray with new cable ties.
  • Now place the tray into your growing tank. The water should be several inches deep but you want it just to be lapping at the bottom of the tray; enough so the plants can access the water bit not so that they are drowning in it. You can adjust the amount of polystyrene to get the float level right.

No you’re system is ready but you need to complete several more tasks before you can start growing your watercress.

Filling The Tank

You can just add water from the tap to your fish tank. But, if you do this you’ll need to turn on your pump and aerator. These should be left to run for approximately 3 days; this will ensure any chemicals in the tap water have gone.

You can add chlorine removing products but if you have the time it is best to let the process happen naturally.

Add Bacteria

Add some ammonia to your fish tank. This will encourage the growth of the bacteria which will convert the fish waste into nitrates for the plants. It is vital you do this before you introduce the fish and the plants.

The process will take approximately 2 weeks which can be frustrating but it will ensure the right environment is created for your fish and watercress.

As a rough guide you’ll need to put one cup of ammonia in and add a capful each day for the two weeks.

It is advisable to test ammonia and nitrate levels every day. When there are very little or none of these you should be ready to bring in your fish.

Dropping The Fish In

Once the bacteria are ready you can add the fish. Don’t forget that they need to be given time to acclimatize to the water. Keep them in a bag of water for several hours before allowing them to swim into the main tank.

You can always start with a couple and then add the others once you’re confident that they are happy and comfortable.

Add Your Watercress

how to grow watercress in aquaponicsThe easiest way to get started is to purchase some watercress seeds. Then line the bottom of your floating raft with cotton wool or hemp fibers; this is your growing media. Sprinkle your watercress seeds across the top of the growing media in the same way you would if planting in soil.

Gently place the tray into the water and wait for them to grow.

It is possible to grow watercress with cuttings if you prefer; just sprinkle them across the tray.

In future years you may wish to retain the seeds from the watercress you have grown; allowing you to produce more for nearly zero cost.

Now sit back, relax and watch how quickly your watercress grows. This is one of the best plants to grow in an aquaponics system and should provide you with a bumper yield. Do you want to grow more plants in your aquaponics setup? Read our guides on the best plants for aquaponics and the best plants for small aquaponics.

Best Plants For Small Aquaponics

Aquaponics done successfully will give you the great satisfaction of looking after fish while growing your own crops. In fact, it is relatively simple to set up your own small system at home. All you need is a tank for your fish, a pump to send this water to the plant bed and return it to the fish and some planting media for your plants.

Of course there are details to sort and fine tweaking that will need to be done but you can easily create a small setup to test your skill and learn what works for you.

The choice of fish is fairly straightforward, most people use tilapia, trout, goldfish, carp, catfish, koi or even shrimp and prawns. Your choice will depend on the type of setup you have and whether you are looking to breed edible fish or are simply keeping the fish to feed your plants.

What is more difficult is deciding the right plants to grow. While most plants do well with aquaponics there are several species that do exceptionally well. You’ll need to decide which type of plant suits you the best. For example, there is little point in growing tomato plants if you don’t actually like them! If you want to know what ratio is good for fish and plants, check it out here.

Here are some of the best plants for small aquaponics:


The humble tomato plant does exceptionally well in this water based system. You will find it easier to control the temperature and even the amount of sun the plants get.

However, it is worth noting that tomato plants tend to attract pests which can be exceptionally difficult to get rid of.


Peppers can be extremely difficult to grow via the standard approach to gardening. This is because they are particular about the water they consume and require plenty of sunshine.

Growing them in a small aquaponics system makes sense. You will be able to monitor the temperature of your set up and make sure the nutrient levels in your water are optimized. But, more impressively is the ability to produce extremely hot peppers as you can turn the temperature dial right up for them.

It is worth noting that peppers do not do well in a constant water type aquaponic system. However, they do exceptionally well if you use the flood and drain approach.

This means flooding the growing media with the water for 15 minutes and then allowing it to drain for 45 minutes. You’ll need a pump and a timer to ensure this happens all the time without your interference.


aquaponics strawberryThese little red fruits are great to eat all year round. This is actually possible with a well setup aquaponics system; the plants don’t need to know that it’s winter!

To grow strawberries in a small aquaponics system you’ll need to have as many plants as possible. This is because most plants will only produce a few strawberries; if you want to enjoy eating them or even sell them; then you need to have plenty of plants to create the yield.

The good news is that each plant needs very little space and you can use the floating raft system, tubes or even baskets. Strawberries need very little care to flourish and make a great plant for first time users.

Plants That Don’t Like Aquaponic Systems

There are always some plants that find it difficult to thrive in an alternative system to their natural home. It is best to avoid trying to grow any of these:


Blueberries may be delicious and healthy but they also have a low pH tolerance; they grow best when the pH is below 7. This can make it difficult to keep the pH level right in the water for the fish and the plants.


This plant also has an issue with pH but they like growing media with a pH over 7; again this is likely to be an issue when maintaining the right environment for your fish.

Unless you are particularly passionate about these types of plants then anything that wants pH levels well in excess or below 7 is not a good bet for your aquaponic system.

The Bottom Line

Aquaponic systems are not new but they have received a lot of attention in recent years. Much of this is because they are a great way to grow virtually any plant. At the same time; crop yields can be greatly multiplied and the environment better controlled.

You may be looking for the best plants for small aquaponic systems but the reality is that even your small setup is part of the future; aquaponics offers the opportunity to grow far more crops and help feed the world.

One last thought that is worth considering is that vegetables and other products which grow in the ground will grow well in aquaponics but there shape may not resemble the one that you are used to; they will still taste delicious though. The best plants for small aquaponics are tomatoes, strawberries, lettuce and peppers.

Aquaponics plants that have been proven to be very successful

Aquaponics gardening is continuing to pick up speed all over the world. When it comes to organic gardening there is no better option to choose aside from this one. It is simple but not until you really understand what it is you are doing and the plants that you can grow in an aquaponics system. Basically, aquaponics is a combination of hydroponics plus aquaculture. In simpler terms you can harvest fish and grow plants in one system. It is the waste from the fish that provides the growing plants with a food source while they in turn act as a natural filter for the water the fish are living in. It is a symbiotic relationship; a win-win situation.

What plants can you grow? 

There are so many aquaponics plants that you might want to try out in your system. Initially it was thought that only water plants would work for the system. However, it was discovered after lots of research that terrestrial plants were a very effective way of purifying water for the aquaculture. The nutrients in the water were ideal for growing plants in the hydroponic system. So what are the plants that you can grow in your system?

Leafy crops such a lettuce, chives and kales were the first considered for aquaponics. Nevertheless commercial growers have enjoyed great success with plants such as tomatoes, melons, flowers, cucumbers, basil, mint, broccoli, cabbage and so many more. The list is endless. Terms and conditions apply though. It depends on the method that you choose. There are people who choose the nutrient film technique (NFT) others work with clay pebbles etc. There are plants that grow best with one method and not with the other. Read our post about the best plants to grow in aquaponics. Check out this article if you want to grow small plants in aquaponics.

It is important to have a good ratio between plants and your fish. Click here to learn more about it.

Plants with clay pebbles 

clay pebbles

Clay pebbles in an aquaponics system are only used to grow plants that have a low nutrition demand. Some of the best examples of these plants include kales, mint, arugula, swiss chard and watercress. Most common house plants will do well in this system. A temperature in the bracket of 60-80°F will work perfectly for most of these plants. The only thing that you will need to ensure is that their need for air and pH of the water is kept at its optimum. In the case of lettuce, the leafy varieties are favored ove the iceberg lettuce.

Plants with nutrient film technique (NFT) 

NFT is an aquaponics method that is best for plants that require a lot of nutrient content. The plants are grown in long narrow channels and a thin film of water flows continuously down these channels. This system is best for plants that need lots of water such as the aforementioned leafy vegetables. With careful control of the amount of water it is possible to grow fruiting plants such as tomatoes, cucumbers, capsicum, broccoli, peas, peppers and peas. These ones however require lots of nutrients and will normally grow under temperatures in the neighborhood of 78°F. Spring and summer are the best times to grow these plants using the NFT method.

Bottom line 

In summary, there are just so many aquaponics plants that you can try out both in large scale and small scale. The only thing that you need to master is the control of water and the temperature of the water. Leafy vegetables such a lettuce and kales do not require high nutrient content like tomatoes, cucumbers and other fruiting plants.