Pipes, pumps and emitters are the puzzle pieces for a proper irrigation system. Everything should be designed to work together based on how you grow and how the site is laid out. Pictured: A pressure-compensated precision distribution system. (Provided by Urban-Gro)

Irrigation systems: Why commercial cannabis growers should go with the flow

Pro Growing: Five considerations for irrigation systems that every commercial cultivator needs to know

One of the fastest-growing trends in commercial cannabis cultivation is installing irrigation systems.

This focus on efficiency can cut production costs for large-scale cultivators, while increasing consistency and uniformity.

The two most common setups I see in existing facilities utilize either hand watering, or a rudimentary drip system without any emitters at all. In both scenarios, you won’t get uniform application, which leads to inconsistent plant growth and headaches abound. To get uniformity, you need a properly engineered, pressure-compensating system.

Here’s a breakdown of why a good irrigation system is well worth the time, effort and expense:

Zoning: Manage many as one

I don’t disagree with the small-scale grower who says every plant needs individual attention, but the way we look at it on a large scale is by utilizing irrigation zones to batch hundreds or thousands of the same strain (or similar) into groups that are managed as one.  Whether an irrigation zone is 500 square feet or 5,000 square feet, it doesn’t matter.

Generally speaking, you want one genetic per irrigation zone, and plenty of closely related strains can be grown on the same irrigation zone. Group the plants that need the same amount of water and the same nutrient recipe so you can grow them as one. You don’t have to be any less attentive to the plants, you’re just managing many as one.

When healthy rooted clones start off, they may be growing at slightly difference paces, but if they’re placed in the same designated irrigation zone, you can get the plants leveled out quickly. Another benefit to plant uniformity is employees find more rhythm in their workflow. They can move down the line without having to make decisions about every plant.

Batch mix or nutrient injection?

Nutrient injection is a complex topic and I’ll devote a future article to it. In the meantime, I’ll say hand mixing nutrients is time consuming and is vulnerable to costly human error. Nutrient injection systems are reliable, time-tested systems that never call in sick or need to take vacation. As each injector has a cost, in order to be economical, you do need to pare down the number of nutrient concentrates to eight or fewer, plus pH adjustment. If you have the budget and just can’t bear to let go of that Cannabis-Cup winning 20-ingredient recipe, then batch tank mixing might be the way to go.

Pro Growing: irrigation column
The pipe size and water pressure for a cultivation room’s incoming water source are key factors for initial setup. Pictured: An auto-monitoring, high-capacity irrigation assembly. (Provided by Urban-Gro)

Fertigation design

The devil is in the details when it comes to designing the distribution system. This is when you determine the size of pumps, pipes, filters and emitters. Everything should be designed to work together based on how you grow and how the site is laid out.

Among the factors to consider: How many strains are you growing? Do you want to pulse feed or give one big dose per day? In order to decide emitter flow rates and emitter type, what substrate do you grow in and how much substrate per plant? Drip stakes work well for rockwool and smaller pots (5 gallons or less), but larger pots lend themselves to spray stakes to improve coverage.

The flow rates always need to be regulated by pressure-compensated emitters to ensure uniform application. Pressure loss occurs across any length of pipe, so using emitters that compensate for the fact you could have 50 pounds-per-square-inch coming in to the pipe and only 20 psi at the end of the length ensures all your girls are getting the same amount of feed.

These days, people rarely forget to make sure they have enough power in a building, but just as important, what pipe size and pressure is your incoming water? This will determine if you need to add a holding tank to store water or whether you can run straight from the tap, storing just emergency water. Also, modern variable frequency drive (VFD) pumps allow for greatly varying zone sizes, so retrofitting a facility with large and small rooms is not a problem. Definitely work with an irrigation engineer or someone who can make sure your pumps and pipes are sized appropriately.

Controlling the system, a.k.a. “The Brain”

After you have your pipe, pumps and emitters selected, you need a way to control the flow of water through the system. Simple landscape irrigation controllers available for less than $100 at home improvement stores can suffice, but functionality is greatly limited. There are now programmable logic controllers (PLCs) that allow easy monitoring and management of a system from a smartphone or tablet. These may be more expensive, but I have found them to be worth every penny. You can even program how many gallons of water you want to go out if you connect to a flow meter or control irrigation events based on accurate, research-grade soil moisture sensors.

For even more peace of mind, a complete control system allows a grower to manage his or her nutrient recipes, distribution volumes and frequencies from the same dashboard used to monitor the climate, all with a base-model system. There’s nothing like getting a notification from a tireless computer when an irrigation doesn’t go out as scheduled!

Preventing clogging

Growers often worry about clogged emitters or other malfunctions of a precision system. However, with minimal regular maintenance, these systems are extremely reliable and cost-effective. You can flush the system of organic nutrients nightly (which is easy with a good controller) or drain the distribution lines with simple flush valves. It’s also worth the effort to inject an oxidizer into the lines every couple of months. You can let the solution sit in the line overnight and flush it out the next day. I find that doing this between vegetative and flower cycles is plenty to prevent bio-film buildup, and I am a big fan of organic additives.

Final thoughts

When properly engineered, a commercial fertigation system is as good as your best employee and has an enviable return on investment when all things are considered. I truly believe this is the most cost-effective way to ensure uniformity with irrigation. This is the foundation for large-scale success.