What is a Raft Based Aquaponics System?
The Raft System of Aquaponics also known as Deep Water Culture (DWC) is one of the most efficient aquaponics systems for food production. Raft systems are often used in commercial aquaponics due to their mass production capability.
What is the Raft Based System of Aquaponics?
In a raft system also known as Deep Water Culture (DWC) or Floating System, the plants are grown on rafts (polystyrene or foam boards) that float on top of the water in the raft bed. The nutrient-filled water flows continuously from the fish tank through the filtration process, then to the raft tank where the plants are grown and finally, back to the fish tank. Most often the raft tank is separate from the fish tank. (3)
The beneficial bacteria primarily live in your biofilter or media beds but also in the raft tank and throughout the system. A raft system and can be an easy aquaponics system for the beginner aquaponics gardener to set up and maintain.
Since the development of aquaponics raft systems (DWC) on a commercial scale by Dr. Rakocy at the University of the Virgin Islands. Many commercial aquaponics farms utilize this type of system because it allows the plants to grow faster and yield more crops. The Raft system is best suited for mass production of small leafy vegetables like lettuce. (4)
Components of a Raft System
A fish tank is essential in any aquaponics system. The fish tank is where your fish will live and the tank acts as the collection reservoir for fish waste. The fish waste and water will be pumped to the plant beds, providing them enough moisture and nutrients for their growth. (5)
This is the place for the plants to grow. Floating rafts are usually constructed from styrofoam or other lightweight material lined with foam. Plants are placed in holes on the rafts allowing their roots to dangle into the water. Net pots are often used for added stability and to prevent the plants from falling through raft into the system.
A biofilter is a place for the bacteria to colonize. This is where the beneficial bacteria turn fish waste into usable, nutrient-rich food for the plants (5).
The particle filters capture the solid waste from the fish, plant material, and anything that might find its way into the system. Filtration in aquaponic systems is very important, solid particles, fish residual foods, and fish waste can create a serious problem in your aquaponic system. They can clog your piping, nozzles and plant roots and cause unwanted damage to your system. (5).
The water pump is used to pump water from the fish tank, through the filters, and into the grow beds. Pumps are also used to recirculate the water in raft systems and to keep the water moving through the system. (5)
Aeration is the addition of oxygen into the water with the use of ambient air. Adding more oxygen to the water is important for the health and growth of both the fish and the plants. Air pumps, diffusers, air stones or other methods might be used. (5)
Strengths and Weaknesses of the Raft System
- High productivity of crops with low labor requirements. (6)
- Plant roots are more exposed to water nutrients.
- Simple and can be the most economical to build of all aquaponics systems.
- Plants are easy to harvest since roots are submerged into water and not in any media.
- The volume of water in a raft system ensures that it is more stable in terms of water quality and temperature than other systems.
- Easy maintenance as rafts beds is easy to clean. Since rafts can be placed in the tank itself, it allows for the efficient use of space.
- Suited for home gardens, hobby applications, and commercial production.
- As purification occurs continuously it allows for higher stocking of fish.
- Somewhat restricted to growing small leafy greens like lettuce and basil.
- Unsuitable for root vegetables and some fruit plants.
- It can be a mosquito breeding ground if not designed correctly. (these may be controlled by using guppies or mosquito fish)
- Water can evaporate at the gaps between raft edges and the tank it is kept in.
- Needs filtration since the roots are completely immersed.
- Filtration process increases costs, besides requiring regular filter-cleanups. (If using a filter and not media beds)
- Roots are susceptible to microbial attacks or may be consumed by herbivorous fish. (6)
- There is little surface area for beneficial bacteria to grow.
- Because the roots are completely submerged, the addition of oxygen through aeration is often required.
Plants to grow in a raft system
Small and lightweight plants are the most suitable for growing in a raft system. Vegetables that grow best in this system enjoy a moist environment and have a small root system and structure.
Lettuce and Leafy Greens
Raft Systems are ideal for growing lettuce and leafy greens since these plants love moisture and have a minimal root system. Additionally, lettuce has a short growing cycle and a relatively low height, they don’t need staking to support them. Growth time 5 to 6 weeks from seeds. (7)
Basil is a unique plant and allows growers to get a higher yield. By pruning basil regularly, growers increase the production of the branch and control the shape of the plant. Growth time 8 to 10 weeks from seeds. (7)
Although kale is a healthy leafy vegetable, it doesn't grow particularly tall. Kale is not a nutritionally demanding plant and hardy enough that it can be matched to any type of fish in the system. Kale likes cool temperatures and can be harvested either fully or partially. Growth time 5 to 6 weeks from seeds. (9).
The collard greens family refers to either cabbage or broccoli, both of these plants are durable. Growth time broccoli 7 to 8 weeks from seed, cabbage 7 to 8 weeks from seeds. (7)
With little temperature regulation, chard will produce delicious, buttery-tasting leaves and can be harvested either fully or partially. Chard makes for a durable, tasty and easy to grow plants in a raft system. Growth time 4 to 6 weeks from seeds. (7)
Factors For Choosing Raft System Plants
The best plants for the raft system or DWC are small and lightweight. The rafts are generally durable and affordable but they can only support limited weight. Top-heavy plants can fall over or break at the stems without root anchoring provided by a dense media. (7)
Raft systems function on a single horizontal plane since they are too heavy to stack. If you have limited space, consider an approach that can facilitate denser growing plants. Be sure to match your plant site spacing on your rafts to your plant size. (7)
Choose plants that are thirsty plants that will thrive in a raft system, so pick seed varieties that love water like lettuce. Drought loving plants will not do well in this system. (7)
Ensure that the plant will provide you with a profit if you’re growing commercially and good harvest if you’re growing for home use or as a hobby. (7).
Rafts System Tips
With these simple tips, the raft system can be excellent for mass production and easy to maintain. Here are a few tips on running and maintaining a raft system. (8)
- Aeration is the key. This should be maintained regularly to make sure your plants and fish have plenty of oxygen to live and grow. The water needs air added either by pumps or air stones or some methods that will help increase the dissolved oxygen content.
- Test the pH level and temperature of your water regularly to ensure that it is within the appropriate range and the nitrification process is operating.
- Check the pumps and any piping regularly for proper functions and remove any solid materials from the filters that might clog or block.
- To ensure maximum yield from your system, use plants and fish that are easy to care for, grow quickly, and are disease resistant.
Other Types of Aquaponics Systems
Media Based System
A media-based aquaponics system is the growing of plants in a large container that is filled with media. The growing media used is usually either gravel or clay pellets and is where your plants are grown. The bed is regularly flooded with water from the fish tank. The water then drains back to the fish and all waste including solids are broken down within the plant bed.
This system is one with the fewest components, the solid waste is broken down throughout the media removing the need for an extra biofilter. The production in this type of system might be lower than the other methods but the amount of beneficial bacteria found in the media bed is essential to any size system. For this reason, we prefer a hybrid system where we have both media beds and raft beds working together.
Read our article, what is a media-based aquaponics system to learn more about the media-based system.
Nutrient Film Technique (NFT)
The Nutrient Film Technique (NFT) is a method of aquaponics in which the plants are grown in a long narrow channel. NFT is both common in hydroponics and aquaponics due to its simple yet effective design.
In NFT a thin film of water flows continuously down each channel, providing the plant roots with water, nutrients, and oxygen. When the water reaches the end of the channel it is pumped back to the fish tank. NFT uses both water and pumps to deliver nutrients to the plants and the system requires separate filters to clean the water of solid biological waste before it returns to the fish tank.
This system is very efficient in its water use and is primarily used in cultivating greens that have small roots systems. NFT is commonly used in the commercial aquaponic system but can also be used in hobby or backyard aquaponics systems. (3)
Raft systems are one of the simplest aquaponics systems to set up and is one of the more common methods used for commercial and mass production. The rafts can be reused for many cycles of planting once the plants are harvested. The raft system method is an easy method that can be built by a beginning aquaponics farmer. In the next article, we will discuss the “Nutrient Film Technique System of Aquaponics”. Subscribe to our newsletter to be notified when a new article is published.
- Aquaponic Vegetables, aquaponics, Commercial Aquaponics, Deep Water Cuture, Floating System of Aquaponics, Lettuce, Organic Gardening, plants, Raft System of Aquaponics