dwc marijuana

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!