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  • How to Grow Hydroponic Plants in Deep Water Culture: The Complete Guide

    February 29, 2024 9 min read 0 Comments

    deep water culture bed planted with lettuce heads

    Introduction to Deep Water Culture

    Curious about Deep Water Culture (DWC) for your plants? This easy-to-follow guide takes you through the essentials of DWC, a straightforward hydroponic method. Here, you'll learn the keys to keeping plants thriving in water and explore simple raft systems and advanced bucket techniques. In this article, growing expert Andy Russo breaks down DWC for us.

    deep water culture raft board with lettuce under purple lighting

    Understanding Deep Water Culture (DWC)

    Deep water culture is one of the simplest forms of hydroponics. Deep is a relative term here. We are generally in the 12-24” depth range, although I have seen custom systems with a much more substantial nutrient solution depth. The plants in a DWC system are grown on a raft floating in a large raft bed. A raft bed is the reservoir and the grow media for the plants. Smaller deep water culture systems are also popularly made with net pots set in a lid or 5-gallon bucket lids with net pots incorporated into the design.

    The main question that arises surrounding a deep water culture system is, “ Why don’t the plants drown?” This is a good question that goes back to the basics of Hydroponics 101. In these systems, water is aerated aggressively. It's essential to keep air stones clean and the intake of the air pumps clear of obstructions. The plants are suspended in water, and if we do not aerate our buckets or raft beds adequately, the plants will certainly drown. The aeration introduces oxygen into the water that keeps the plants from drowning. 

    While deep water culture does not require water pumps, they can be incorporated into a system to ensure a more consistent nutrient solution in a large-scale raft bed. However, in DWC, one of the main advantages is the simplicity and minimal required equipment and consumables.

    Why is DWC an Important Hydroponic Method?

    Deep water culture can be a straightforward system; you can set up a raft bed to use only a starter plug at each planting site. This means you only need to clean your raft bed, raft, and air stones. It is an easy system to keep clean and can be sized to an impressive scale. 

    The DWC method is where my hydroponic adventures began, and that is not out of the ordinary. These systems are extremely forgiving and inexpensive to set up and run, and the maintenance is minimal.

    deep water culture bed with boostrap farmer raft and lettuce starts

    Getting Started With Deep Water Culture

    Key Equipment Needed for DWC Setup

    For a raft bed system, you will need a raft bed and rafts. The raft bed is usually a steel frame and a liner similar to that used in a pool or pond. The rafts have been made of high-density polypropylene almost exclusively. The material is extremely buoyant and reasonably durable. 

    Bootstrap Farmer's Deep Water Greens Rafts are coated with a  with polyurea coating, eliminating many of the common issues growers have with deep water rafts breaking down adding to replacement costs.

    DWC rafts will often have a precut planting site. This helps to hold a small starter plug so new seedlings or starts can have support until they fill the planting site hole with more root mass. 

    For a bucket or reservoir system, you will need buckets with net pots set into the lids. Depending on the size of the net pots, you may need a grow medium (we do not want light in the reservoir!). I personally like a DWC bucket system that uses clay pellets. With this combo, the only consumables from the grow cycle to grow cycle are nutrients and air stones (no need to replace every cycle, but as they age and are cleaned, they lose their efficiency.)

    Advantages of Deep Water Culture for Plants

    High Yield Potential with DWC

    DWC systems can give you impressive yields for the system operating cost. The yields are supported by a robust root system that is submerged in nutrient solutions 24 hours a day! This is a huge advantage in the plant's ability to uptake nutrients. The plants are going to be constantly taking in nutrients and water. 

    As the water needs to be topped off, we can adjust our additional nutrient solution to maintain a TDS (Total Dissolved Solids) within the range we have chosen to be acceptable for the crops we produce. This will involve testing the remaining solution and then finding the TDS of the new solution we need to add in order to mix the two and end up with a solution at the correct TDS. For the small amount of hassle, this will help save money on fertilizer, boost yields by ensuring the plants have a stable and balanced nutrient solution, and reduce cropping time.

    The Ease and Efficiency of DWC

    Deep Water Culture is an efficient system in several important ways. First and foremost, we are running the minimum of equipment. This saves time and money and makes it easier to afford spare components to keep on hand at all times, which can help us avoid costly downtime.

    It is common to start seedlings and cuttings in a small plug, and once transplanted, there is no need for a larger volume of grow medium. 

    lettuces plugs in 1020 trays being planted by a farmer

    The savings on growing media and the shipping of media can not be understated. Efficiency at its finest, the system can be run on clay pellets (that can be sterilized and used repeatedly) and your choice of starter plugs. Your plants get access to everything in the nutrient solution 24/7.

    This is a huge bonus, and as long as you are strict about your nutrient solutions parameters, it will yield exceptional results.

    lettuce plants in a raft in a deep water culture bed

    Recognizing the Challenges of Deep Water Culture

    Possible Disadvantages in DWC Systems

    Water cleanliness

    DWC systems’ simplicity and cost-effectiveness does come with a few considerations. The weekly water change must be considered if you are growing in 5-gallon buckets with a net pot lid. The size, weight, and form of the crops you are producing can make this chore nearly impossible. Vines can be destroyed, especially if they are bearing heavy fruits. If you can not get your bucket out from under the grow light you may have height issues when lifting a fully developed root structure up and out of that bucket come water change time.

    Water weight and surface choice

    Deep Water Culture raft beds can be large, and water weighs in at 8.34lbs per gallon. With hundreds and sometimes thousands of gallons in a raft bed we need to be absolutely certain we have a stable, level surface. Uneven beds can cause issues up to and including complete structural failure. A thousand gallons of water weighs 7340 lbs. and will absolutely blow out a greenhouse wall. 

    As you can see, problems arise when we attempt to set up a system in the wrong grow space or fail to prepare the site. 

    Troubleshooting Common DWC Issues

    The beauty of DWC is the few issues you can have. The air pump can die, but this is obvious and most crops will survive several hours minimum with a dead air pump. 

    The air stones can get clogged if you do not clean them weekly. I like to keep an extra set around to make sure I can swap them out if they break (which will happen) or they are dirty and I don't want a gap in the aeration of the nutrient solution.

    If you have plant pathogen issues in the root zone, flushing several times can help, and running a diluted hydrogen peroxide water mixture can help kill problem pathogens. Still, If we do our water changes and keep a clean system, you will find DWC very user-friendly.

    All other issues in the system (aside from lighting or crop pests) are nutrient solution ppm, pH or temperature-related. 

    Exploring Variations of Deep Water Culture

    The Kratky Method Vs. Traditional DWC

    The Kratky Method uses some of the same principles of DWC while making it even more basic. In the Kratky method, we use a reservoir or bucket with a net pot and fill our reservoir to the plant's roots. That is where the similarities end. 

    In the Kratky Method, we fill the reservoir with nutrient solution at the beginning of the grow, and then we do not change or top off the reservoir at all. The plant drinks the water, and as the water is drawn down the reservoir stays humid enough to support roots while also allowing feeder roots to harvest more and more oxygen from the reservoir. 

    The Kratky Method relies on there being enough water for the plants to finish their whole growth cycle. This alleviates the need to lift the plants and net pots up to change water, which means the reservoirs do not need to be as accessible until harvest. 

    The benefits of DWC, to me, are fairly clear. We can increase yield and available oxygen and nutrition with a weekly nutrient solution change and an air pump. This leads to a cleaner and more consistent availability of nutrients in our nutrition solution.

    The beauty of the Kratky System lies in its simplicity, and it is a viable method of growing. I would, however, encourage anyone looking to give this method a try to add an air stone after a cycle of the Kratky Method. You may find the minuscule added expense of the air pump, and stones will be totally forgotten when you are harvesting undoubtedly larger yields.

    Recirculating Deep Water Culture (RDWC)

    When we string DWC buckets together, we need a current to mix the nutrient solution evenly and keep the nutrients in the water in the solution. If we simply filled a reservoir attached to several buckets with nutrient solution, we would not be getting much if any, nutrition to the buckets farthest from the reservoir.

    If we simply add a water pump to the reservoir and an emitter to each plant in each bucket, the water will be drawn from the reservoir and then pumped to each plant, creating positive pressure from the weight of added nutrient solution, creating a flow of water back to the reservoir, feeding our water pump and continuing the recirculation of our nutrient solution. 

    Optimizing Your Deep Water Culture System

    How to Maintain the Proper Nutrient Solution Levels

    When the crops are young and do not need the same level of nutrition, a large reservoir may not need to be changed as often. The seedlings cannot take up any more than they need and a large reservoir can be kept at the correct level of nutrition using your pH and TDS meters. 

    I suggest checking the reservoir at least twice a day. I prefer morning and evening (based on your grow lights if indoors) as this will tell us where we are at the beginning of the day and after daytime conditions are concluding. This ensures you know what is happening and, just as importantly, when symptoms were first evident. 

    After a few grow cycles, you should nearly be able to predict your readings depending on what day in the cycle you are. Take notes, they are invaluable. As they say, "No two gardens are the same on the same day, and no two days are the same in the same garden." (Hugh Johnson)

    Role of Aeration in DWC

    I will never stop saying, "You will not be able to put too much oxygen in your nutrient solution.” You will make the root zone too turbulent for the plant's roots before you add too much oxygen to your nutrient solution. If you are looking at things to upgrade, get a bigger pump. If you have a big air pump, buy more air stones. If you have all of that, get spares.

    Redundancy is invaluable in hydroponics. I have had some frantic trips to the hardware store at 9 pm because I did not believe in redundancy early on in my hydroponics journey.

    Embrace the Power of DWC for Hydroponic Growing

    DWC hydroponics are incredibly user-friendly, easy to set up/customize, and can accommodate nearly any crop at any stage of development. I do want to focus, again, on the simplicity. This system has very few moving parts, and as a new hydroponic grower, it is a fantastic way to get used to going through the motions of checking PH, checking TDS, the effects of nutrient solution temperature on specific crops, frequency of water changes, etc. These systems allow a grower to really hone in on their water quality and the importance of cleaning with a system that has a very wide margin for error.

    If you are a new grower or simply want to increase yields without looking to complicate your current operation, I highly recommend DWC.

    Frequently Asked Questions (FAQs)

    Is DWC suitable for new growers?

    These simple systems are how I fumbled my way through learning to grow hydroponically. In the 15 years since, I have tried nearly every system. I still suggest a DWC system to everyone I have ever consulted. They are very rewarding and reliable. 

    How often should I change the nutrient solution in the reservoir?

    Change your nutrient solution weekly, even if it doesn't look dirty (I make sure to give my nutrient solution to garden plants, trees, and shrubs when I do exchanges.) Add fresh water when crops get large enough to bring the water level down substantially in less than a week.

    You can test and add nutrients, but you are going to have nutrients that are not in the same ratio that they are intended to be for the crop you are growing. The plants have been munching on the nutrients and we can't know exactly what they were taking up and what they were not using without costly water tests.

    Every time you change nutrient solution, clean your air stones, and any air lines, and wipe out any grime in the corners of your raft bed or the bottom of your buckets. If you clean every week, you will have a reasonably enjoyable chore. Wait for smells or a mess; you may lose your whole crop, and you will most certainly loathe this chore!