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Root zone health is a wealth for growers

November 15, 2021  By Mohyuddin Mirza

Figure 1 Photo Courtesy: Mohyuddin Mirza

A plant’s root zone can make or break a business, and is especially important for cannabis plants as each gram of bud matters. Therefore, it’s important to have a peek inside the root zone. 

Defining the root zone
The roots are the foundation of a cannabis plant. When seeds germinate, the plant’s first priority is to produce root, the energy coming from the embryo inside the seed. All the planning for roots and shoots is already done in the seeds.  

There are various types of root zones and what can be accomplished at the top if the zone stays healthy. In Figure 1, the roots are hidden in a one-gallon plastic container with a soilless growing medium consisting of peat moss, perlite, vermiculite, and additives to adjust the pH. In Figure 2, the roots are in a five-gallon pot with coir as a growing medium, and top of the plant showing some nutrient deficiencies. The plants in Figure 3 are in a five-gallon pot where commercial soilless growing mix was used, and the root zone was well managed. Rockwool blocks were used in Figure 4, for commercial production. Here, the root zone dynamics would be different and therefore, watering and nutrients would have to be well managed. In Figure 5, the roots are in an aeroponic unit. Root zone is determined by the root volume, air around the roots, and nutrients directly sprayed on the roots. 

Root zones will vary depending on the growing medium in which they are growing. Therefore, the physical, chemical, and biological characteristics of growing media will define the root zones. Root zone characteristics will change as plants grow and with all the inputs, like water and fertilizers. It’s crucial to keep the root zone healthy and by looking at the top of the plant, one can see what is going on the root zone.   


Role and function of roots
Roots are used as an anchor so that the plant doesn’t tip over. In soil-grown crop, it’s very evident how cannabis plants withstand wind and other stress factors. In greenhouses and indoor situations, the anchoring function is used less, with the tops supported in a net. There are two major functions of the roots that growers must understand. One is the absorption of nutrients and the other is growth and development. Essential nutrients are absorbed and transported to locations where they are used for growth and other functions. Additionally, food manufactured in the leaves are transported to the roots and put toward energy for growth.

Food transported to the roots can leach out in the surrounding growing medium, which the microbes can utilize. If there are ‘good’ microbes like mycorrhizae, they will use that leaked food and in return, colonize the roots and provide protection from ‘bad’ microbes. 

Growing mediums and root zone health
A plant’s growing medium composition establishes the benchmark information for how your crop will grow and flourish. It’s crucial to know about  different growing media and how root zone health would be impacted during watering and fertilizing.

Commercial soilless media: is prepared from peat moss, which provides the bulk fiber, water holding capacity, nutrient holding capacity and exchange, and air porosity for roots. To improve air porosity, perlite, and sometimes vermiculite, are added for improved water holding and cation exchange capacity. Then regular lime, calcium carbonate, or dolomite lime, calcium-magnesium carbonate is added to counter the low pH of the peat moss. Remember that it takes a good two to three weeks before lime has fully reacted to water and provides the desired pH in the root zone. Some companies will provide these media amended with mycorrhizae or other beneficial organisms for root zone. Nutrient charges are also added to meet early needs of the cannabis plants. Ensure you have all the information on physical, microbial, and chemical characteristics of the growing medium you plan to use. 

Coir (coco-fiber) or coir-based growing media: can be used as such, or added to a soilless growing medium. Root zone health in pure coir is determined by the quality of the material as determined by coarse vs fine fiber, amount of coir dust, and buffering treatments. One of the biggest determining factors of root zone health using coir, is ensuring it’s pre-washed properly to remove the sodium and/or sodium that has been exchanged with calcium. Cation exchange capacity (CEC) inherent to coir is also beneficial when looking to improve root health.

Rockwool: is basically an inert material and oxygen dynamics are different than other growing media. The water and nutrient management are far more influential in determining the root health in this case. 

Aeroponic systems: no growing medium is involved and root health depends on irrigation and nutrient inputs. With no buffering in the root zone, managing the root zone health is crucial. I’ve seen critical mistakes with crops grown in an aeroponic system and not enough attention was given to buffering provided by bicarbonates. Results were damaged root zone and poor top growth. 

Other factors affecting root zone health
There are two major factors that affect cannabis root zone health. One is the plant itself, which can change the pH of the growing medium. During  veg stage, the pH heads in an alkaline direction, while during bud stage and under stress situations, the pH will head in an acidic direction. The second is the oxygen dynamic determined by irrigation protocols. This is a detailed subject on its own and is sometimes handled on its own. 

Key factors to keeping your root zone healthy 

  • Learn about your growing medium through its composition, physical, chemical, and biological aspects.
  • Know what the roots are telling you. Plenty of root hairs, reasonably white colour, and good branching are positive signs, while brown and slimy roots aren’t.
  • Control your inputs. Watering frequency and quantities have a major impact on root growth absorption of nutrients. Avoid temperatures that are too cold and too warm in the root zone. 
  • Plan nutrients based on what you want the plants to do; know your strategies.
  • Avoid water logged conditions. That is the number one disease issue due to depletion of oxygen. 

Mohyuddin Mirza, PhD, is an industry consultant in Edmonton, Alta. He can be reached at

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