“It all starts in the root zone, growers who can efficiently manage the root zone are going to cover a major part of plant management that’s ultimately going to optimize plant health and crop yield.” This is how Anthony Domangue of the Fohse horticulture team started the webinar in which some of the most important steps for proper root zone management were highlighted.

Select the right growing media
The first step highlighted in the webinar was the importance of choosing the right growing media, as every media has different properties in terms of water it can hold and how it holds onto nutrients.

“When deciding on your media, it really comes down to two things: environment and irrigation strategy. Outside temperature will play a significant role in the temperature and humidity within your facility. Humid areas could, for instance, consider a growing media with a lower water holding capacity to avoid overwatering and root rot. Drier ones could likewise go with one with a higher water-holding capacity, such as peat-based media. As for the irrigation strategy, the main tip is to think about it logically. If you use a media with good dry back potential while attempting to hand water, it will result in some problems. Typically, you’re going to see a need to have more irrigation events, which isn’t really feasible with a small staff, for instance. For those who water by hand, media with a higher water-holding capacity is therefore better. It all depends on your irrigation strategy.”

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Crop steering techniques
After choosing the correct media for your facility, step two will be implementing crop steering techniques as they pertain to irrigation or how to manipulate the growing inputs to achieve the desired result. In the case of the webinar, it was about how to stimulate the inputs to achieve more vegetative or generative growths depending on your goals.

Vegetative cues are meant to help optimize the growing speed, stem elongation, foliage development, and root development. Think of cues like frequent irrigation events (like every 30 minutes). “With those frequent irrigations come small dry backs, and ultimately, you’ll have a large irrigation window when you steer vegetative.”

Small irrigation events are another vegetative cue having to do with the shot size of irrigation, meaning the irrigation event that you feed to your plant in the amount of fertigation that you're feeding. “The shot size is between 1 to 3% of the total substrate volume, not your field capacity. To find this, you’ll want to take the substrate volume in liters and convert it to milliliters. For example, a 3% shot size for 7570ml substrate is going to be a 227.1 ml shot.”

Generative cues are essentially intentional stress placed on plants. This signals the plant to produce flowers or seeds and is achieved with opposite cues compared to vegetative cues. Large irrigation events (4 to 6% shot size) and infrequent irrigation events (no sooner than 30 minutes between events), as well as high substrate EC, will result in large dry backs and a small total irrigation window.

Utilize substrate sensor technology
According to Anthony, step three has to do with an issue many growers can find themselves in as they face challenges with plant nutrition or managing how much water volume they are giving the plants.

“One way to alleviate that is by using a substrate sensor. When the sensors of the device are inserted into the media, it can monitor water content, temperature, and EC in the substrate, which is valuable software to have. Many devices also track these metrics over time, so you have a timestamp of what you did and adjust where needed. Without these tools, you can’t really align the results you got with the decisions you made.”

Collect runoff date
The next step aligns well with the previous one, as it is again about collecting data. “Data about the plant's runoff spent water, or nutrient solution emitted from the bottom after the growing media has achieved field capacity, says a lot about how your plants are uptaking nutrients. If you already have your inflow feed and substrate sensors at the root zone, to complete the picture of what’s going on with your cultivation, a good look at the runoff is important. For example, a low pH runoff typically means that calcium, magnesium, and potassium will be less available for plants to uptake in the root zone. High pH typically means less magnesium and zinc.”

To properly collect this data, Anthony provided four steps:

  • Pour a pH-balanced nutrient solution at normal feed concentrations into the growing media until you achieve field capacity. You’ll typically see a visual but slow drip.
  • Wait about 30 – 45 minutes to allow the solution to be absorbed by the growing media.
  • After step two, prepare a small container with reverse osmosis water that is pH-balanced.
  • Pour a very small amount of pH-balanced R.O. water into the media until you achieve 40 – 60ml runoff, 50ml being ideal for an accurate pH and EC reading.

Managing root zone under high light intensity
Implementing a higher light intensity is a huge change in the grow. It drives photosynthesis, so as you increase this plant metabolism, some other changes need to be made to avoid the plant's health becoming out of balance.

“This starts with understanding the lineage of each variety you grow. Parental lineages are going to greatly influence how your cultivars grow and how they express themselves. For example, some varieties that were bred and selected for their performance under the intensities and spectrum of HPS fixtures may not be able to push as high of light intensity sometimes because their peak performance was under those settings. When you alter that, they start to fall out of their optimal balance. With high light intensity in mind, you’ll want to select varieties whose parents grew in conditions with naturally high light levels or newer hybrid genetics with some high light preferring varieties in its lineage.”

The second step in managing your root zone under a high light intensity is to increase the feed concertation. “A higher concentration of nutrients is needed to meet the higher rate of the plant metabolism. With the increase in feed comes a subsequent need to increase the EC in the media as well to avoid nutritional deficiencies. The levels of this vary per variety.”

Another step to take is altering your irrigation strategy after defoliation. According to Anthony, it is common in the cannabis space these days to strip their plants. It does stress your plants, but when used properly, it’s going to increase airflow into your canopy, which will mitigate the risk of any mold or PM issues. Additionally, it will increase light intensity on your lower canopy, increasing the photosynthesis on your lower. “That being said, you can use too much defoliating and then ultimately stunt your yield. It’s important to dim your light intensity a bit for the next 24 to 48 hours, as your plants will be very stressed and going to slower rates of metabolism. To meet those needs, you’ll need to alter your irrigation strategy to decrease the total fertigation volume that you're feeding.“

With this, Anthony concluded the webinar before going into the Q&A, in which some clarity was given about the subjects discussed.

The full webinar can be watched on Fohse’s YouTube channel.

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