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Setting Up Deep Water Culture (DWC) In 5 Easy Steps

If you’re into growing marijuana, you’re probably aware that using a hydroponic system has a lot of benefits over growing in soil. What stops most growers from getting familiar with hydroponic cannabis cultivation is the idea that this is much more difficult than growing in soil. We already discussed how this isn’t necessarily true in our “7 Easy Steps To Start Growing Cannabis In A Hydroponic Setup” guide, but didn’t talk about Deep Water Culture (DWC) at all! DWC is often regarded as “the most difficult” way of growing marijuana, in this article we’ll try to convince you it’s actually quite easy.

Of course, the best part is how cool the roots look without any medium!

1 – The Reservoir

When growing marijuana in a deep water culture hydroponic system, the reservoir is where all the magic happens. Plants are suspended above the nutrient solution, where the entire root ball is submerged. Make sure your roots do not receive any light to prevent problems, the easiest way to go about this is by using thick, black plastic containers.

A cannabis plant needs a reservoir with a minimal volume of around 10-15 liters to complete its life cycle, ideally each plant gets its own reservoir for this. You can definitely grow multiple plants in one reservoir, but this does mean you can’t adjust nutrition as specifically. Use highly uniform strains or clones if you intend to grow more than one cannabis plant per reservoir.

These two plants are growing in the same reservoir, but the one in the bottom looks like it’s a week ahead! Different phenos can make feeding a lot more difficult.

A large scale DWC hydroponic system will often use a large central reservoir that is connected to multiple smaller ones. This way you only have to mix one big barrel of hydroponic nutrients and hook it up to the system to feed all your plants. These recirculating deep water culture (RDWC) systems are definitely the way to go if you want to scale up your grow room, but aren’t required for smaller grows. If you’re just starting out with deep water culture, we’d recommend running a single reservoir with a single plant. With a few weeks of veg time you can fill out smaller tents quite easily with only one cannabis plant.

If you want to use deep water culture on a larger scale though, a recirculating system is the way to go!
Big plants like this can easily put 5 kilos of pressure on your DWC bucket lid.

2 – Pots For A DWC Hydroponic System

The actual pot your cannabis plant is supposed to grow in is often left out in discussions about deep water culture. Ideally you’d use net pots that are specifically designed for use in a hydroponic system, but these are relatively unavailable throughout Europe. More experienced DWC growers know how to make decent containers out of just about anything, but this can be difficult for newer growers. Fortunately there are plenty of options if you’re a bit creative, we’ve seen anything from modified outdoor pots, to nets or baskets being used to hold up plants in DIY hydroponic systems.

Net pots are specifically made for growing in a hydroponic system, but these aren’t available everywhere unfortunately.

Problems with these DIY pots usually involve the holes in the bottom being too small or too sharp, which can really damage a plant’s root system. Our favourite DIY solution is to burn as much holes as possible into a 200ml container using a soldering iron. The shape of these pots also makes it very easy for them to be held in place.

A soldering iron makes clean holes with rounded edges, but make sure you do this in a well-ventilated area.

You’ll usually fill this container with hydroton clay pellets, lava rocks, perlite or another inert medium with low water retention. We prefer hydroton clay pellets for their ease of use and availability. You can technically germinate directly in these pots, but it’s much more reliable to germinate in a starter plug. Any starter plug is fine really, but we prefer rockwool cubes for practical reasons.

In our general DWC workflow we germinate a seed in a rockwool cube and transplant it into the container a day or two after germination. You’ll still have to top water your cannabis plant during the very early stages unless you incorporate a drip system. As soon as the roots hit the water however, your plant will start to explode.

A top drip system like this will make the first week or two much easier, but won’t do much after that. We’ll leave it up to you whether this is worth the effort!

You can also start at a higher water level for the first week or two, keeping the bottom of the container just barely under the water line. The water level should be much lower for the remainder of the grow however, as a root rot is always a threat. Containers should be a good couple of centimeters above the water line for majority of the grow cycle.

In this image you see a cannabis plant in a DWC system. The two diagrams on the left side include a water pump because the plant requires top watering as long as its roots can’t reach the nutrient solution yet. Once the roots start touching the water this wont really be necessary anymore and the plant will start growing explosively.

3 – pH, Nutrients And Additives

A big drawback of DWC is that it also requires quite specific reservoir temperatures, ideally 17-20 °C. This is the reason this type of hydroponic system is hard to pull off well outdoors. For the average home grow however, this range is easily maintainable. During heat waves you can lower the temperature by adding a frozen bottle of or two or using an aquarium chiller. Cold reservoirs can be heated up using an aquarium heater. If you are attempting to grow in a location with very variable temperatures, it might be best to reconsider DWC entirely.

If you only have heat issues for a few weeks per year, the “hillbilly chiller” method of throwing in a bottle of ice is usually the most practical and cost-effective.

As we already discussed in our “7 Easy Steps To Start Growing Cannabis In A Hydroponic System” article, the average hydroponic system will be quite finicky when it comes to pH. The pH value of your nutrient solution is the most likely culprit when anything goes wrong in a DWC grow. Ideally you’d keep your pH at 5,8, but anywhere between 5,2 and 6,2 should be fine. A DWC hydroponic system might not require new nutrients as often as other systems, but you should definitely measure and adjust the pH regularly. Using diluted pH-down can make adjustments in a smaller dwc grow system much more practical. Nutrient lines that include a buffering component like Advanced Nutrients’ pH Perfect and Canna Aqua are especially practical in DWC grows, but not essential. You’ll have to check pH regularly either way, but a more stable pH is easier to maintain and much better for your plants.

Growing marijuana in a DWC hydroponic system means these two meters will become your best friends quickly!

Most DWC growers will recommend refreshing the entire reservoir every week or two, but you can get away with less. If you keep an eye on your ppm/EC values, you can usually avoid draining your reservoir for the majority of a grow. As the reservoir is drained, you can tell how much nutrients a cannabis plant uses by tracking differences in ppm or EC. If this information is used well you can usually completely avoid emptying reservoirs until the final flush.

Ideally your plants would use nutrients at the same rate as the water they’re dissolved in, but differences will generally arise at some point. In many cases a cannabis plant will use much more water than nutrients. If values remain the same or drop as the water level goes down, you can safely add another dose of nutrients. If ppm/EC values rise as the water level drops, you should only top off with pH adjusted water.

The “clean” way to run DWC is by refreshing the entire reservoir at every feeding. The “quick and dirty” way to do it is by refilling your reservoir indefinitely. This chart shows how you should top off your reservoir to maintain a ppm value of 1000.

If you choose to maintain reservoirs this way we do recommend always running enzymes, as this will help prevent a buildup of waste and unused nutrients.

4 – Aeration For Your Cannabis Plant

The next step to setting up your own DWC hydroponic system is to figure out how you’re going to aerate your reservoir. The main advantage of DWC is that a cannabis plant will have unrestricted root growth, but this strongly depends on an abundance of oxygen in the reservoir. Without an air pump, DWC is simply not possible. DWC growers should always have a backup air pump, as a day without a pump will most likely kill your crop.

Choosing an air pump can be very confusing when first building a DWC hydroponic system as there is little and confusing information online. Pumps are usually rated by how much air they provide per unit of time, in this article we’ll use liters per hour so adjust accordingly if you’re using imperial units. We’ve seen recommendations going from 1 l/h per liter of reservoir, all the way up to 15 l/h per l. While lower is better for most parameters when growing marijuana, the opposite is true for aerating your reservoir.

Air pumps are cheap and effective, this little 35 euro pump produces 3600 litres per hour.

We recommend getting a pump with at least double the liters per hour as the volume of your reservoir. For a 25 liter tank, we’d get at least 50 liters per hour of air flow. This doesn’t have to break the bank at all as cheap, 10 euro DIY store aquarium pumps often already produce around 100 liters per hour. Cheap pumps are fine, but make it extra important to have a backup pump close by. A single air stone per plant is technically enough, but we recommend using a second airstone just to be sure.

Components in air pumps are often installed without being 100% secured, which means they vibrate and make a lot of noise! You can fix this by gluing any vibrating parts to the body of your pump. Make sure you work safely though!

The capacity of your pump might not always be the main issue. A common mistake when setting up a DWC hydroponic system is not plugging in the pump until the very last moment, only to find out it makes more noise than your car. A stealthy DWC grow is usually limited by the sound of the air pump, so make sure you check this before buying anything. After buying a pump you can often reduce the noise by hanging it up and gluing any vibrating parts stuck. If you are set on using a larger pump you can also build a noise reduction chamber around it, similar to the way this is often done with exhaust fans.

5 – Strains For DWC

First and foremost, any strain will do well in a deep water culture hydroponic system as long as you give it the attention it needs. There are however big differences in how much attention different strains need. Because growing marijuana in a DWC hydroponic system goes hand in hand with floppy plants, shifts in pH and nutrient concentration and high humidity, it is a good idea to pick a strain that deals well with these issues.

Our Gold Bar Kush isn’t the easiest strain in the world, but performs extremely well in DWC!

Strains like our Jack F1 and Strawberry are amazing strains to grow, but they are more difficult to grow in DWC because they don’t like shifts in pH or nutrient concentration. More robust strains in terms of these shifts like Afghani Gold and Mega Power Plant are much less likely to be stalled by changes in the reservoir. Indica varieties are generally a little easier to grow in a hydroponic system, but that doesn’t mean sativa strains are incredibly complicated. Sativas will require more support and possibly more training due to their height, while indicas are bushier and usually need more defoliation.

Most strains are developed for either outdoor soil systems or indoor hydroponics, so make sure you buy a cannabis strain that was developed with hydroponics in mind. Many of our strains were selected for their viability in hydroponic systems, so a large part of the Spliff Seeds catalogue is very suitable for DWC. Strains like our AK and White Widow deal well with high humidity, changes in nutrient concentration and pH shifts, making them ideal strains for growing marijuana in a DWC hydroponic system.

Final Thoughts

By breaking down the workflow of growing in deep water culture, we hope the idea behind this type of system has become a little less complicated. DWC requires a few parameters to be well organized, making it an excellent way to learn how to work with hydroponics. Once you have all these parameters dialed in though, growing is suddenly very easy and you’ll understand why people like growing in hydroponics so much. Give it a shot, we wish you the best of luck growing in this amazing hydroponic system!

If you’re into growing marijuana, you’re probably aware that using a hydroponic system has a lot of benefits over growing in soil. What stops most growers

Deep Water Culture: Your Questions Answered!

by Sirius Fourside

Have you ever heard of hydroponics? Although the term is sometimes used to describe growing cannabis plants in any inert or soilless medium (for example coco coir), it more commonly is used to describe growing with plant roots directly in water and that is what most people think of when they hear the word ‘hydroponics’.

Cannabis Plants Growing With Roots Dangling in a Reservoir of Water

Here’s what’s inside! Since the cannabis roots get everything they need without having to “search” for it like they would in soil, you end up with faster vegetative growth rates. This growth is supported by huge masses of happy, healthy roots like this!

“Deep Water Culture” (commonly referred to as DWC) refers specifically to the type of hydroponics where plants grow with the roots stretching out into a tub of nothing but aerated nutrient-water.

This roots-in-oxygenated-water setup is what gives Deep Water Culture its remarkable vegetative growth speed!

Why is it called Deep Water Culture? “Deep Water” because the plants are growing in a deep pool of water instead of in some sort of growing medium, and “Culture” is a word that can also mean “Cultivation”.

As DWC has gained popularity for growing marijuana, we have been receiving lots of questions from hydro growers of all experience levels. Today, I’m going to answer some of the questions we see the most, as well as give you some helpful tips that will make your next DWC grow much easier and more rewarding!

Sirius: Also, I’ve mixed in some pics of my current DWC grow. It’s like a quick timeline of a cannabis plant’s life in a DWC setup.

What is DWC?

In short, DWC is growing your plant with its roots in aerated nutrient-water (the air part, provided by bubbles, is very important). Like this:

(Click the picture below to see an animated version [3Mb .gif])

Do plants really grow faster in DWC?

Yes, plants grow noticeably (and I mean noticeably) faster in DWC during the vegetative stage than they do in soil or coco coir.

Why is that? Vegetative plants growing in soil spread out a huge system of roots, then they use those roots to search for and uptake nutrients from the soil in which they live. Roots in soil also need to find pockets of oxygen to prevent the plant from “drowning”(lack of oxygen is what causes plants to droop from being overwatered).

When growing hydroponically, the roots don’t need to spread out, and they don’t have to ‘search’ for the nutrients since everything the plant needs is readily available in the most absorbable form possible. The dissolved oxygen in the water gives the roots almost unlimited oxygen and prevents the plant from getting “overwatered” or droopy even thought the roots are living in a reservoir of water. This decreased effort in having to ‘find’ nutrients and oxygen translates into increased vegetative growth and lots of foliage, especially if plenty of light is provided!

However, while buds may fatten up more in the flowering stage due to great environmental conditions at the roots, possibly increasing your yields, they won’t be ready to harvest any sooner after the flip to 12/12. The time to harvest is mostly dependent on strain, and DWC-grown plants take the same amount of time as any other plants to fully ripen and be ready for harvest. (Why Aren’t My Buds Ready for Harvest?)

Is DWC harder to do than soil?

Nope! Every method has its own quirks you have to watch out for, but with a little experience and a good setup, DWC can be just as easy as soil (if not easier) since it ends up taking so little time to manage.

Here’s a DWC setup in action!
Barneys Farm Liberty Haze Barneys Farm Critical Kush

Should I try DWC for my first grow?

Although DWC is a great (and my personal favorite) way to grow, I would definitely recommend trying coco coir as an introduction to growing cannabis. It is similar to a hydroponic grow in many ways, and will teach you most of the skills you will need to grow, but it a little bit more forgiving. I personally think coco is one of the best ways to get introduced to growing cannabis!

Once you‘ve completed a grow with coco, DWC will seem much easier. That being said, we’ve received many pictures from growers doing DWC amazingly well on their first grow just by following the tutorial!

I’ve already grown in soil. Do I need to be concerned with anything new when growing DWC?

When it comes to Deep Water Culture, the main difference if you’re used to a hand-watered growing medium is you need to pay attention to the reservoir. Peeking into the reservoir through an empty net pot hole lets you ensure the roots look happy and that the water level inside is properly maintained. It’s just like paying attention to your soil except that the conditions of water can change quite a bit faster. On the flip side, you have much greater control over the root environment in DWC than any other grow method!

Do I need an air pump?

Yes, it’s absolutely necessary! Your plant roots still need air, and without an air pump they will drown. Plant roots need oxygen, and the heavily oxygenated water in a DWC reservoir is a big part of why hydroponic plants grow so fast!

This is a time-lapse video of the seedlings from the last picture growing over 13 days.

Can I have the air pump turn off sometimes to save electricity?

I would strongly recommend against it; the air pumps should be running for 24 hours a day throughout your grow to give your plant roots lots of air and bubbles. Besides, it’s the grow lights that use the vast majority of the electricity.

If you’re worried about the noise, placing the pump on a solid, thick surface instead of directly on the floor will reduce the vibration quite a bit.

Is DWC safe to do?

Most definitely! Just make sure you don’t have electronics/plugs/outlets directly on the ground. This is a rule for all grows, however.

Is DWC as stealthy as other grow styles?

Slightly less so. A DWC setup requires an air pump to be running, and air pumps can make some noise depending on the model you get. Larger air pumps vibrate harder, which can become its own separate kind of noise!

Luckily, there are many models that pump out lots of air and run very quiet! EcoAir makes a pump that will run two large stones and you can barely tell it’s on. Placing the pump on something thick and solid (instead of directly on the floor) will reduce the noise even further!

Unrelated Tip: Exhaust fan too loud? Try hanging your exhaust fan from inside the tent instead of setting it on top; this will greatly reduce the amount of noise!

3 of the seedlings from before have been culled, and now only the strongest plant from each strain remains.

(Culled all but the two strongest plants; I prefer to have only one per container.)

How should I start seeds in DWC?

Rapid Rooters are – in my opinion – one of the best ways to start a seedling in DWC. They germinate successfully so often for us that that now if a seed doesn’t germinate, I assume the seed must have been a dud. The main thing to keep in mind with Rapid Rooters is to make sure they stay moist, but they should never look or feel wet. If it’s shiny, it’s too wet!

My second favorite germination method is the Paper Towel Method. It is simple but surprisingly effective at getting seedlings started fast.

Does my reservoir water need to be sterile?

No, but it has to be a good place for plant roots to live. Some people take the route of keeping their reservoir sterile – meaning it just has nutrients and water and no trace of anything alive.

Personally, I load my reservoir up with beneficial bacteria instead. This way, if bad neighbors like pythium (a fungus-like organism that causes root rot) move into my reservoir, they get out-competed by the good guys that already live there. There are a few good sources of beneficial bacteria for DWC, but I personally use Botanicare Hydroguard, which is a root supplement that is extremely effective at stopping and preventing root rot in a DWC environment.

With all the root space and light to themselves, two little plants soon turn into bulky shrubs!

Why does the pH of the nutrient-water go up right after I put it in the reservoir?

The pH of the water in a reservoir can change for many reasons, but when it happens right after you changed the reservoir, it may be because the water was sitting for a while and is now being agitated. Bubbles from the air pump move the water around, especially on the surface; this movement raises the pH of the water in addition to aerating it. This may be less noticeable if you shake your water up well before testing the pH and adding it to your reservoir.

In any case, after about an hour, you should notice the pH stays more stable (and that’s the pH level you should pay attention to).

There are a few other factors that change your pH over time. Your roots give off waste products that affect the pH, and as roots use up nutrients at different rates that can also alter the pH.

One thing you can do to help stabilize pH is keep your water level about 2 inches below the bottom of your net pots. A bigger reservoir has a more stable pH, so making sure your reservoir is always topped off will help improve pH stability. On the flip side, the air gap helps prevent the hydroton from affecting the pH, keeps stems from getting mushy, and also helps roots get more oxygen.

What is Top-Feeding?

Top-Feeding is something you add on to a DWC setup. It takes water from the reservoir and trickles it directly onto your seedling roots to encourage your seedlings to grow faster. This setup is what many people think of as ‘bubbleponics’.

Is Top-Feeding worth the trouble?

Top-feeding provides a very tangible benefit in the beginning of the cannabis plant’s life. Seedlings sprout and grow leaves faster in the beginning, but the benefits will definitely diminish after a few weeks. Once a plant is in ‘aggressive vegetative’ mode with a big root mass in the water, the effects of a top-feed will be practically nonexistent.

That being said, a grower can shave 1-2 weeks off of a grow with top-feeding, which makes the beginning stages a lot more exciting (and saves time / electricity)!

This is low-stress training. The stems are gently bent away from each other and held with twist-tie.

How many plants should I grow in a reservoir?

You can grow as many plants as you can fit, but 3+ will definitely be a crowded fit. As much as it pains me to say it, the most efficient configuration is to grow one plant per container. This gives the roots more room to spread out, but more importantly, it gives the leaves and buds room to spread out! It also gives you 5 extra ports to reach the reservoir without having to actually move your plants and possibly disturb the roots.

Do I really need to check the pH?

Checking the pH can be boring/tedious, but it’s also one of the most important factors in any grow, especially in DWC. Good pH management makes for pretty plants and bad pH makes for sickly plants. Think of pH adjustments like a supplement that makes your plants grow better and faster!

How often should I give new nutrient water to plants growing in DWC?

You can change your reservoir water for new nutrient-water every one or two weeks, but in the meantime they need to have the reservoir topped off with pH’d nutrient water at 1/4 strength. After a grow or two, you’ll notice that some strains (like BlackJack) will throw a fit if their water isn’t changed weekly, while others (like Wonder Woman) are hardier and can handle a wider array of conditions.

As a general rule of thumb, you should completely change your reservoir at least once every two weeks in the vegetative stage, and at least once a week in the flowering stage.

Cannabis plants respond well to low-stress training, like these ones from above. They filled up all of the empty spots we made!

How can I easily drain and replace the reservoir water?

A liquid transfer pump (also called a ‘water transfer pump’) is typically used to empty out aquariums or transfer gas between containers and a vehicle. If you’re growing cannabis in a DWC (Deep Water Culture) or similar setup, this type of tool can turn the often arduous job of changing your reservoir water into a quick 5 minute task!

The one I use is pictured here. This “battery-operated siphon liquid transfer pump” uses D batteries so you don’t have to worry about cords. This means that people who grow hydroponically don’t have to plan their grow area for the sake being able to empty/fill their reservoir more easily. It’s a good choice for hobbyist growers with 1 or 2 small reservoirs, though if you’ve got a big tank you’ll want something more powerful that can move a lot of water.

What are optimum nutrient levels for growing cannabis in DWC?

Always start with half of the recommended dosage on the schedule provided with your nutrient system. For example, I use General Hydroponics Flora Trio, so I just use the schedule on the back of the bottle divided by 2.

After that, dial it in! That means to watch your cannabis for signs of nutrient burn or deficiency. If it gets nutrient burn, reduce the nutrients from 50% to 25%. If it’s becoming lime green and the pH is between 5.5 – 6.5, increase the nutrients from 50% to 75%.

Buds are forming on the army of branches we made!

These plants are about to be defoliated one last time before harvest!

Can I mix up the nutrient water in advance?

If you’re using General Hydroponics Flora Trio, then the answer is yes! And that’s straight from the horse’s mouth! …the horse being General Hydroponics.

Although I haven’t confirmed this with every hydroponic nutrient company, colloquially, it seems that there is no problem at all with storing pH’d nutrient-water for up to a week as long as the nutrients don’t contain organic ingredients (like guano, kelp, bloodmeal, bonemeal, etc).

When in doubt, always contact your nutrient company to see how far ahead you can make your water! Most major nutrient companies have a contact form on their website and will get back to you in just a day or two. They know their products better than anyone!

What temperature should my reservoir water be?

Here’s the rule I use: If your grow room temperature is in a good range, then your reservoir temperature is also in a good range. You only really need to worry about your reservoir temperature if your grow room temperature is out of the acceptable range.

Many growers aim for their reservoir water to be between 60-68°F because cooler reservoir temps prevent some bad organisms from growing in the first place, and cool water can hold more dissolved oxygen in the 60-70°F range. However, cannabis can grow and thrive in much warmer reservoir temperatures as long as beneficial organisms are present to fight root rot. In fact, I personally have found that hydroponic plants tend to grow a little slower when their roots are cool, and grow fastest around 75°F (as long as you’re using a supplement with beneficial organisms to kill root rot).

Maintain the temps in your grow room and the reservoir is fine

I personally have found hydroponic plants tend to grow the fastest when the temperature is between 73-80°F, with 75°F being a good temperature to aim for. However, with warmer temps make sure you’re using a beneficial bacteria supplement to prevent root rot!

They’re just fattening up under the 600w HPS light! Due in about 4 weeks!

Deep Water Culture (DWC) means growing your plant with the roots in a bubbling reservoir of nutrient water. This perfect root environment is what gives DWC-grown plants their remarkable growth speed!