Deep Water Culture (DWC), also known as Direct Water Culture or a raft/pond/float system, is a method of hydroponics in which roots of plants remain submerged in an oxygenated solution of nutrient-rich water.
Unlike other systems of hydroponics, the nutrient solution is not made available to the roots at regular intervals. Instead, roots are suspended in the water 24/7.
The method is called “deep” water culture because often the water in the reservoir must be at least 10 inches deep.
How do DWC systems work and what are the advantages?
Let’s dive deeper.
How DWC Systems Work
- A reservoir contains water with all essential nutrients dissolved in solution.
- The water is oxygenated with air pumps through the use of air stones.
- A lid that covers the reservoir contains holes to hold net pots.
- Net pots often are filled with some growing media like Hydroton or Rockwool to hold the base of the plant.
- Seedlings are placed in the net pots, whose roots stay submerged in the nutrient-rich water.
- The solution provides the roots with the necessary nutrients, water, and oxygen.
Why Air Stones Are Important
You may fear that the plants may die if their roots are continuously exposed to water.
That’s where air pumps and air stones come in.
Oxygen in the water quickly depletes as plant roots take in oxygen, and it needs to be replenished constantly. Otherwise, the roots may suffocate and drown in the water, which can kill the plant.
Air pumps pump in air (duh) which is then diffused throughout the water through air stones. This establishes a uniform supply of oxygen throughout the solution.
You can easily find air stones and pumps in pet and aquarium stores.
Advantages of DWC
- Easy and inexpensive to set up.
- Accelerated growth and a larger yield due to better uptake of nutrients and oxygen.
- Requires very little maintenance.
- The pH, Electrical Conductivity(EC), water temperature won’t fluctuate in a large DWC system as much as in an NFT system, due to the relatively large size of reservoir of nutrient water available for each plant.
- Requires less nutrient mix compared to other systems.
Disadvantages of DWC
- A pump or power failure could make the water run out of oxygen and can be harmful to plants.
- The pH, nutrient content, and water level may fluctuate wildly in small systems.
- If a plant develops a disease, it can spread to other plants easily if they share a connected or common reservoir.
- Water temperature can increase due to the continuous running of the air pump and be difficult to maintain.
- In small systems, it may be easy to over or under calibrate.
- You need to transplant germinated plants into DWC systems, you can’t sprout seeds directly.
Types of DWC systems
Deep Water Culture systems have their own variations. Here, we’ll cover 4 different types:
- The Kratky Method
- Recirculation DWC (or RDWC)
- Commercial DWC
The Kratky Method
The Kratky Method is the simplest form of DWC and a completely passive growing method because this system works without any pumps, electricity, or wicks.
In the Kratky Method, the reservoir isn’t completely filled with nutrient water, but instead, a gap is provided between the top of the roots and the surface of the nutrient solution, meaning the root is not completely immersed in the water and a small part of the root is exposed to air.
As plants grow, they reduce the water level in the reservoir as they take in more water. This creates an ever-increasing air zone in the reservoir that meets the growing oxygen need of the roots.
Roots in the air space above the surface of the nutrient water are called “aeration roots” and the roots that extend into the solution are called “oxygen and nutrient roots.”
After you’ve made sure the water contains all of the necessary nutrients and set up the reservoir, your plants will have access to the nutrients, water, and oxygen they need throughout the entire growth cycle.
The best thing about the Kratky Method is that, unlike other hydroponic systems, you don’t need to change the nutrient water once you’ve set it up. No additional labor is required after planting until it’s time to harvest.
Here, the complexities associated with aeration of roots and circulation of water are avoided, and the crop is harvested before the nutrient solution becomes fully exhausted.
Here’s a video about the Kratky Method featured in our article on 7 DIY Hydroponic Systems.
Recirculation Deep Water Culture (or RDWC)
In traditional deep water culture, each bucket needs to be checked individually for pH, nutrients, and water level. This can become tedious and time-consuming if you need to grow a lot of plants.
In Recirculation Deep Water Culture (RDWC) the buckets are connected together, most commonly using PVC pipes.
A pump is used in this method to circulate water through all the bins. Each connected unit has its own air stones to oxygenate the water.
A separate bucket, called the central or control bucket, connected to the system is used to check and modify the pH, nutrients, temperature, and condition of water for the entire system.
A downside to this system is that diseases can spread easily to other reservoirs due to the easy transfer of pathogens.
Commercial Deep Water Culture
Commercial Deep Water Culture uses a large pond as the reservoir in which plant roots are immersed.
A raft that contains holes to hold the net pots covers the pond. The water is oxygenated and chilled to temperatures to maintain proper dissolved oxygen concentration.
This method is most suited for growing small plants such as lettuce.
While in basic DWC systems there’s no drip system used, in bubbleponics the nutrient water is also directly fed to the roots of the plants from the reservoir, in which the roots are (or will be) suspended, using irrigation tubes and a water pump.
This method is a combination of the drip system and the deep water culture system. The water from the net pots runs back to the reservoir below. Here, too, the water is oxygenated using air pumps and air stones.
Bubbleponics is particularly useful in the initial stages of growing plants using DWC, where the roots of the plants in the growing medium haven’t yet grown long enough to reach the water in the reservoir.
Plants That Grow Best In DWC Systems
While you can grow almost any plant that can be grown hydroponically with DWC, one thing that matters the most while choosing your plants is the weight and size of the plant, especially in commercial raft systems.
This is because your raft needs to be strong enough to support the plants.
Deep water culture is most suited for small, lightweight plants and leafy greens such as lettuce, spinach and basil.
If you choose to grow taller plants like tomatoes and cucumbers, you need to have them trellised, since they can topple or break at the stems due to loose anchoring of roots.
Lettuce is the most common grown plant in commercial DWC.
The following are some plants suitable for DWC:
- Bok Choy
- Watermelon (single plant)
- Grapes (with trellis)
- And most herbs like parsley, oregano, coriander, mint.
Best Growing Media For DWC
Growing media help provide support to the plants since the roots are loosely hanging in the nutrient water.
In DWC, it’s best to select growing media that have good moisture-retaining properties and wicking potential.
This is useful when starting to grow your plants as it helps roots to pick up water thrown upwards by bubbles from air stones.
Some of the best growing media are the following:
- Rockwool, a fibrous material formed by spinning molten rock or minerals
- Hydroton, or expanded clay pellets
- Coco coir, made from fibers extracted from the outer husk of coconuts
Managing pH and Nutrients With DWC
As said earlier, the pH, nutrient level, and EC of the water don’t fluctuate very much due to the increased buffering thanks to the large reservoir of nutrient-rich water, so they should be easy to maintain.
The best pH for hydroponic plants is around 5.5-6.5, though this can vary depending upon the plant. The pH of the water has to be in a suitable range for plants to absorb nutrients.
You can adjust pH by adding a pH down (an acid) or a pH up (a base).
Prepare the hydroponic nutrient mix by combining water and the nutrients your plant needs. It’s better to add a little more than what you think is enough for the plants.
In simple systems like the Kratky Method, after you’ve ensured that the water has the correct pH and nutrients, you don’t need to add any additional nutrients or modify the properties of the water until you harvest the plant.
In other types of DWC systems though, you need to change the water regularly. How frequently you renew the water depends on the size of your plants and nutrient reservoir.
You also need to keep the water level stable, so if the water level has dropped significantly, you need to replenish the water and nutrients in the reservoir.
3 Things To Keep In Mind While Setting Up Your DWC System
Ready to get started? Here are 3 things to keep in mind.
DWC buckets and tubing
The buckets or reservoirs that you use for deep water culture must be opaque and light-resistant to prevent the growth of algae. The same applies to the tubes that connect the air stones with the air pump.
Don’t forget LED grow lights if you’re growing your plants indoors!
In DWC systems, water needs to be chilled to temperatures between 65°F-80° F in order to maintain proper dissolved oxygen concentration.
Chilling the water down also helps prevent pathogens like pythium, delays bolting, and allows for increased nutrient solution efficiency. Lower temperatures also cut down the chances of root diseases significantly.
How to chill your water
- The most effective way to maintain a cool water temperature is to use a water chiller.
- Painting the outside of the reservoir white helps in reflecting light away.
- Keep your reservoir in a shady and cool place.
Deep Water Culture: Final Thoughts
DWC is the simplest and purest form of hydroponics that’s easy to set up, where plant roots are suspended in a nutrient solution and aerated by air pumps.
The main advantage is a large and increased yield.
- The Kratky Method is the simplest method and suitable for beginners.
- RDWC makes maintenance easy by connecting several buckets together.
- Commercial systems are useful for growing a lot of plants.
- Bubbleponics is used to accelerate growth at the initial stages.
So, what are you waiting for? Get growing!