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.
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!