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Deep Water Culture: Your Questions Answered!

When people think of the word ‘hydroponics’, they think of growing with lots of water. Although the term ‘hydroponics’ includes mediums such as coco coir, the term originally referred to growing your plants with their roots in water.

In that sense, Deep Water Culture is true hydroponics. It’s growing your plant with the roots stretching out into a tub of nothing but aerated nutrient-water. It’s this roots-in-water setup that gives Deep Water Culture (commonly referred to as DWC) its remarkable vegetative growth speed!

As DWC has been gaining popularity, we have been getting lots of questions from 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 plants 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, but only while in the vegetative stage. Plants grow noticeably (and I mean noticeably) faster in DWC during the vegetative stage than they do in soil or coco coir.

Vegetative plants 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. When growing hydroponically, the roots grow and spread out, but they don’t have to ‘search’ for the nutrients since they’re available in the water provided. This decreased effort in having to ‘find’ nutrients translates into increased vegetative growth and lots of foliage if enough light is provided.

However, while buds fatten up more in the flowering stage, DWC-grown plants take the same amount of time to fully ripen and be ready for harvest (since that is dependent on strain).

Is DWC harder to do than soil?

Nope! Every method has it’s own quirks you have to watch out for, but with a little experience, 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 Critial 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. Once you‘ve done that, DWC will seem much easier. That being said, we’ve received many pictures from first-time growers doing DWC amazingly!

Do I need to be concerned with anything new when growing DWC?

When it comes to Deep Water Culture, the only new thing you’ll need to watch is the reservoir. This is to make sure the roots look good and that the water 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.

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.

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 grow lights that use the vast majority of the electricity.

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 it’s 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. Now if I could only silence my exhaust fan...

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 - the best way 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.

Does my reservoir water need to be sterile?

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

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 - the even better replacement for their old "Aquashield" root supplement.

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 go up for many reasons, but when it happens right after you changed the reservoir, it’s usually because the water is 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. After about an hour, you should notice the pH stays more stable and that's the pH level you should pay attention to.

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, but the benefits will definitely diminish after a few weeks. Once a plant is in ‘aggressive vegetative’ mode, the effects will be practically nonexistent. That being said, a grower can shave up to 2 weeks off of a grow with top-feeding, which makes the beginning stages a lot more exciting!

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!

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.

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

How often should I give plants growing in DWC nutrients?

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 plain pH’d water. After a grow or two, you’ll notice that some strains (like BlackJack) seem to want their water changed weekly and others (like Wonder Woman) are hardier and can go for much longer.

How often should I give nutrients to plants when growing in DWC?

Always start with half of the recommended 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 get nutrient burn, reduce the nutrients from 50% to 25%. If they show signs of deficiency 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!

Can I make nutrient water in advance?

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

Although I haven’t been able to confirm this from other nutrient companies, colloquially, it seems that there is no problem at all with storing pH’d nutrient-water for up to a week.

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 should only 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, but cannabis can grow and thrive in much warmer res temps as long as beneficial organisms are present. With that being said, cooler reservoir temps mean most bad organisms can’t grow in the first place, and the water can also hold more oxygen.

In short:

Maintain the temps in your grow tent and the reservoir is fine
Cooler reservoir temps (60-68°F) are optimal, but warmer temps will still do the job as long as the right steps are taken

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