Whether growing indoors, outdoors or in greenhouses, one thing all cultivators strive for is more control. While outdoor farmers are at the whims of weather and are more vulnerable to pest outbreaks, controlled environment agriculture has its own challenges. One of the most pressing demands and perhaps the most puzzling for newer growers is how to establish the right nutrient balance. For decades, commercial growers have increasingly moved to using hydroponic systems to feed and water plants more effectively, and the cannabis industry has taken note.
Growing hydroponically using a soilless medium and relying on water to deliver nutrients helps cultivators control their irrigation and nutrient delivery more effectively and avoid some of the most common setbacks of new cultivators, Bateman says. When setting up a hydroponic system, there are choices growers can make to increase success, and it’s not a matter of “set and forget.” Here, Bateman shares his top tips for getting the most out of hydroponic systems.
1. Install a fertigation system.
A fertigation system is essential and standard when growing hydroponically, as nutrients are delivered via water, which gives growers much more control th
“Your nutrients are instantly available, and you can change them right away,” he says. “So, let’s say you are unhappy with the feed solution or recipe that you are using. The very next time you irrigate, you can theoretically change it and fix that problem right away.”
However, using fertigation systems is not necessarily fail-proof, he says.
“When you are fertigating your crops, every time the plant is thirsty for water, you are also giving it nutrients,” he says. “That can be good and bad, because your plant can just be really hot and just need to move water through itself to cool itself down, and nutrients are just coming along for the ride.”
2. Monitor pH and EC at least weekly.
To get a better understanding of what plants actually need and how they are responding to irrigation and feeding, measuring electrical conductivity (EC) of both the soil and the plant root is key.
“If the salinity of the soil exceeds the salinity of the inside of the root, it pulls water out,” Bateman says. “There are very basic and very complex ways of measuring these things, but you should at least be measuring these things once per week at a minimum. There are sensing probes that growers can insert into their pots that [provide] continuous readings. That’s probably the best way because then you can look at these trend lines every day.”
Growers can also collect leachate after irrigating and use an EC meter and a plastic saucer to measure EC.
“You don’t want to wait until your plants are sick or unhealthy to make a change–you want to monitor that way ahead of time,” he says.
Another metric to watch closely is pH, which can be difficult to treat once it’s out of balance. Growers can work with labs to test water to measure alkalinity and determine if source water needs to be treated, then continue to monitor that for changes from the baseline.
3. Water and feed plants often.
Plants tend to perform best when provided with multiple “little snacks throughout the day,” Bateman, says, rather than providing crops with one heavy meal to sustain them for a day or more. Consistent, small feedings also help to keep EC and pH in check.
“That works a lot better, as it turns out, because roots don’t like big sudden changes,” he says. “So if you go from really dry to really wet as the plant is exchanging ions, EC is swinging, and the plant roots aren’t appreciating that.”
EC levels are maintained with more feedings, and stronger nutrient concentrations are more difficult to control.
“The plant root zone and where it’s sending all the nutrients is like a highway, and nutrients are the cargo, and if I only have one truck that goes up once per day or once every other day, it better be full of cargo. It better last,” he says. “Your pot can only hold so much water and nutrients before it comes out the bottom. If I feed my plants 20 times a day, my EC can be really low because as soon as that plant drinks up that little irrigation shot, it’s drawing that up.”
4. Determine the appropriate amount of fertilizer for your crop.
How often growers are irrigating also helps determine how much fertilizer is needed, Bateman says.
“This is actually the best way of predicting how strong
One common pitfall he sees in the industry is fertilizer overapplication in the flowering stage, as growers try to bulk up plants to increase yield just before harvest.
Maintaining a balance throughout the propagation, vegetative and flowering phases is paramount.
“I treat container hydroponic production in a very classical hydroponic sense–as in, whatever your starting nutrient feed or EC concentration is, I want to see that same EC concentration more or less in your pots. They are never going to be exactly the same, but I want them to be close, allowing for a 20% to 30% differential in either direction before taking action,” Bateman says.
Imbalances are generally caused by overapplying fertilizer, which creates a buildup of nutrients in the container, throwing salinity “out of control,” he says.
“Your plant health is starting to go downhill because your plants can’t take up any more water. You’ve oversalted the earth, and that’s bad,” Bateman says. “But by monitoring pH and especially EC, growers can catch issues early on before they become major problems.
5. Consider using small containers.
Smaller systems complement more frequent fertigation, and nutrients don’t build up as easily.
“Use a small pot that drains well, and use a light, aerated substrate if you can get away with it,” Bateman says, adding that 2-gallon to 3-gallon pots are standard indoors and in greenhouses, when growing with coco coir. For stone wool, most growers work with 6-inch blocks, which equates to about 1 gallon, or finish crops on larger slabs, bringing up the total volume closer to 2 to 3 gallons. Cultivators using peat will often opt for 3- or 5-gallon containers.
Larger containers dryback more slowly, which decreases the optimal frequency of fertigation events, which can create nutrient imbalances
“The longer you wait between every time you feed, the longer you allow for the natural chemistry inside the pot to change,” he says. “Every time you replenish your pot with nutrients and water, you’re helping to balance the pH and control the electrical conductivity, because you are course correcting.”
Other than controlling nutrient delivery, there are other benefits to working with smaller vessels.
“Plants are going to require less pruning, less maintenance, less everything,” he says.
6. Explore reclamation systems, but use caution.
For growers who are using fertigation systems and irrigating frequently, collecting runoff from containers, treating water and incorporating some of it back into the nutrient solution can be beneficial from a financial and sustainability perspective.
But the key is to ensure the water is carefully treated so that any potential disease issues aren’t recirculated throughout the entire system, Bateman says.
“In a recirculating system, you really need to be aware of what the nutrient levels are over time,” he says. “And for that you really need lab analysis, and