Understanding Deep Water Culture and Cannabis Plants

16 Dec 2023

Did you know that you can grow Cannabis plants without a growing medium? Deep water culture is a method of growing plants where the roots hang down into an oxygenated nutrient solution. There are many benefits associated with DWC, including large yields, shorter vegetative times and much more. In this article, we explain everything you need to know about deep water culture, what to feed, and checking pH and E.C levels and mistakes to avoid as a beginner grower.

What exactly is deep water culture?
When growing with soil, the nutrients are already inside the soil, and as long as you add water, the plants will have access to nutrients. There is also a 72-hour buffering period, making organics an easy and forgivable method of growing. 

Deep water culture is the total opposite of using soil, and in fact, there is no growing medium apart from small hydroton clay balls. Using a bucket and lid, an air pump, and an air stone, with a net pot in the center allowing the roots to drop beneath into the reservoir, this hydroponic style of growing Cannabis plants is highly rewarding in the yield department.

For example, if you have a 20 litre bucket, there would be approximately 15 liters of oxygenated nutrient solution bubbling away at all times. The bigger and faster the plants grow, the more root mass will be suspended in a rich cocktail of nutrients. Cannabis plants growing in DWC buckets can grow very large in a short time.

What are the main benefits of growing Cannabis with DWC?

  • Yields can be significantly increased by up to 300% using DWC.
  • Building your own custom sized DWC bucket is cheap and simple to do.
  • Cannabis plants will have access to nutrients 24 hours per day.
  • DWC is a clean and sterile method of growing compared to soil.
  • Using only clay hydroton balls saves money on buying a growing medium.
  • The vegetative period can be made short to avoid plants becoming too big.
  • Mature plants in DWC can grow huge, with a thick main stalk and side branches.
  • The root mass inside the bucket come harvest time will resemble a mop head.

What nutrients will I feed plants in DWC?

You will be using hydroponic nutrients, as using organic nutrients is not an option. Hydroponic nutrients are designed as tiny, bite-sized minerals and nutrients that the plants can easily absorb in water, giving them consistent access to food as and when the plants demand it.

Many nutrient brands will have various hydroponic product lines. You can expect to work with a 4-6 part nutrient line, meaning there will be between 4-6 different products to use throughout the life cycle of the plants. 

How often do I change the reservoir? 
It is important to provide the plants with a freshly made batch of nutrient solution. The reason being that plants will secrete toxins into the water and that the plants will have used up the nutrients from that last solution.  It is a good idea to add a tap to the bottom part of your bucket when making your own version, as this can save time when removing the old nutrient solution. 

When seedlings and clones are still young, you can change the reservoir every 5–7 days; however, once the plants become bigger, it is recommended to make a new nutrient solution every 3–5 days, depending on the strain. Once they are flowering and packing on the pounds, changing every 3 days works well. The temperature of the reservoir should remain consistently between 18 and 25 degrees Celsius.

Checking nutrient strength 

  • The E.C levels of your nutrient mix will determine the strength. 
  • It is best to provide a low E.C level for seedlings and the early growth stage.
  • Digital pens designed for testing E.C and TDS cost around €20–€30.
  • Testing the E.C of the reservoir will dictate how much food the plants use.
  • Not all strains use nutrients the same way, with sativa being more sensitive. 

Checking the pH of the solution

  • All nutrients are accessible to the plants within a certain pH range.
  • Adjusting the pH levels of your nutrient solution is done with pH up or down.
  • Using a digital pen will be the easiest way to check the pH level.
  • DWC requires an optimum pH range of 5.5–6.5.

What equipment will I need to set up a DWC system?

1. Bucket

A black plastic bucket is all you need, and you can find plenty of top quality, food grade ones online. Ideally, working with a bucket that is 20 liters or larger will allow you to grow huge plants and keep your plant count to a minimum.

2. Bucket lid

The lid needs to be flat, firm, and strong enough that you can cut out a hole using a drill to fit the size of the net pot you will place in the top. It is also important that the bucket and lid are opaque, meaning light cannot pass through. 

3. Air pump

You can find a good quality air pump at the local aquarium shop or grow shop. The air pump will be kept on for 24 hours a day, providing dissolved oxygen for the roots. 

4. Air stones

These are what attach to the tubes of the air pump and produce the tiny bubble of oxygen in the water. Basically, imagine a jacuzzi for your roots, and then you will get the idea!

5. Net pot

The net pot will be placed in the center of the lid and will hang down beneath. Filled with hydroton clay balls and a rock wool cube or jiffy for the seedling, the net pot is the only part that contains an inert growing medium.

6. Hydroton clay balls

Hydroton are the little orange balls you often see on display in the local hydro shop when they are showing how the systems work. These small orange clay balls contain no nutrients and are also popular in commercial landscaping.

The differences between DWC and RDWC
Now that you have an understanding of deep water culture, the next best thing, which is far more complicated in terms of setting up and maintenance, is reverse deep water culture.

The way RDWC works is by connecting multiple buckets together using the same pipes. There will be one main reservoir, which then pumps the nutrients through to the buckets. 

RDWC is probably the most complex way of growing Cannabis and is best attempted by those who are well versed in all things hydroponics and are comfortable in plumbing. We recommend learning how to manage and maintain one DWC bucket before challenging yourself with RWDC.

3 Mistakes to avoid with deep water culture

1. Cold temperatures

Cold temperatures inside the grow room will usually mean cold floors and cold DWC buckets. In the event the nutrient solution drops below 18 degrees, the plants will begin to slow down their growth. The best way to combat a cold reservoir is to use a fish tank heater set at 20 degrees Celsius.

2. A drop in pressure

Over Time, air pumps can begin to lose efficacy and sometimes drop in pressure. There can be other reasons why air stones do not bubble correctly. Always make sure that your air pump is properly working and be ready to replace it every couple of harvests.

3. No backup air pump

One of the best pieces of advice we can give is to invest in two air pumps in the event that one stops working. Providing a constant source of dissolved oxygen for the roots is essential, so avoid having only one pump and risking losing your crop in a worst case scenario.