Compare and Contrast: Free-Flow vs Flow-Controlled
Irrigation
The distinction between free-flow irrigation and
flow-controlled irrigation is about as old as irrigation itself, and it serves
as a major dividing line between all the different methods of watering plants.
If you consider the historical origins of irrigation, along the rich riverbanks
of the Nile, Euphrates, and Tigris rivers, it's easy to visualize the
difference between free-flow and flow-controlled irrigation. Relying on the
flooding of a river is free-flow, while using ditches and canals to control
where the water goes and how much of it goes there is flow controlled. I'm
willing to bet that most cannabis cultivators aren't growing their crop on the
banks of the Nile, but many people still choose to irrigate like it's 2500 BC.
We in 2017 are working with far more irrigation options than
our ancestors, and the wide range of watering technology has left us with a
laundry list of different irrigation methods. Each has its own pros and cons,
and many of those pros and cons boil down to whether the method is free-flow or
flow-controlled.
Before getting any further into this article, it’s important
to remember that all of these distinctions are on a spectrum. Within each
category, some systems are “more” free-flow/flow-controlled than others. For
example, a free-flow drip system may be less precise than a flow-controlled
one, but it is still leaps and bounds more precise than a DWC system. The
general distinction between free-flow and flow-controlled systems is important
when deciding which kind of irrigation system is best for your grow, but you
will get much more out of this analysis by understanding that the difference
isn’t always black and white. That being said, let’s get to it!
Free-Flow Systems
Free-flow irrigation is the simplest form of irrigation.
Examples of free-flow irrigation are deep water culture,
flood-and-drain/ebb-and-flow, nutrient film, and some styles of drip
irrigation. Hand-watering falls in a grey area. Methods that involve weighing,
watering, and re-weighing are closer to flow-controlled, while “just spray the
hose at the plant for a while” methods are closer to free-flow. As a general
rule, free-flow methods rely on the plant to take what it needs from a large
supply of water and nutrients, rather than the supply of water and nutrients
being dictated by the grower.
Pros of Free-Flow
One of the biggest draws to free-flow irrigation methods is
simplicity. Deep water culture, or DWC, is about as simple as it gets: just let
the roots grow in a pool of aerated water. This style of irrigation has very
few moving parts (if any at all), is easy to set up, and requires relatively
little maintenance. Ebb-and-flow systems are a little more involved, but still
far less so than a standard drip system.
When it comes to nutrients, free-flow systems offer one big
advantage over flow-controlled systems: they can run just about any nutrient.
It’s pretty much impossible to clog something like a DWC or flood-and-drain
system. Free-flow drip systems lack the small channels used to control flow
rate that standard drip systems do, making them much harder to clog. If you’re
looking to run something like molasses, kelp, or another nutrient mix with high
viscosity or large amounts of particulate matter, a free-flow system is likely
right for you.
The other big benefit of free-flow systems is that they tend
to be less expensive than flow-controlled systems. Free-flow systems are
usually the ones that pop up when you search for “how to grow weed cheaply” or
“grow weed in grandma's house without her knowing,” as it doesn't get much
cheaper than putting a potted plant above a tub of water with an aquarium pump
in it. Many free-flow systems are made using jury-rigged or reclaimed items, or
with standard (and inexpensive!) schedule 40 PVC. Free-flow drip systems cost
less than their more precise cousins because all of the flow control devices –
your spray heads and drip emitters – aren't necessary, and the decreased danger
of clogging means filters can safely be skipped in many scenarios.
Cons of Free-Flow
Free-flow systems are highly inaccurate. Since there is
nothing regulating how much water a given plant gets, it can be near impossible
to know how much of any given nutrient is being delivered to said plant. You
may have 15ml/gallon of nutrient A, but there's no way of knowing what portion
of that gallon went to plant A.
Free flow systems are also very imprecise. Yes, “precision”
and “accuracy” mean different things! Without any flow-control devices, there
is no way to compensate for pressure within your irrigation system. This means
that a free-flow drip system will give far more water and nutrients to the
plants at the beginning of the system than the ones at the end. When you
combine this with the inaccuracy of a free-flow system, you are not only unable
to measure how much of nutrient A your plants get, but you are also unable to
ensure that plant B gets the same mystery amount of nutrients as plant A does.
Both of these cons can be mitigated somewhat with some extra
attention on the part of the grower, but that can require a lot of time that
the grower may not have or be willing to spend weighing plants and measuring
runoff.
Flow-Controlled Systems
Flow-controlled irrigation systems are inherently more
complex than free-flow systems, as they ensure a measured amount of water is
delivered to each plant. Drip irrigation accounts for most flow-controlled
systems, although outdoor sprinkler-based systems are also technically
flow-controlled. If free-flow is a shotgun, flow-controlled is a sniper rifle.
The water and nutrients each plant gets are dictated by the grower, and various
technologies can be used to tailor watering to the needs of each plant.
Pros of Flow-Control
The biggest pros of flow-controlled systems are the biggest
cons of free-flow: flow controlled systems are highly accurate and very
precise. Between the physical emitters themselves and the various automation
options, plants can be fed the exact amount of water and nutrients they need,
exactly when they need them, with minimal waste generated and low variation
between plants. Pressure compensation allows growers to ensure that each plant
is getting fed the same amount as all the others on a given system. This
precision and accuracy takes the guesswork out of budgeting for nutrients and
greatly reduces the logistical problems that runoff can cause.
Flow-controlled systems are also famously flexible. By their
nature, free-flow systems force a grower into a one-size-fits-all irrigation
scheme. Flow-controlled systems let the grower tailor their irrigation to
plants of different strains, maturity levels, and growing media. A
flow-controlled drip system doesn't restrict how you need to grow the plant,
either. A flow-controlled system can be used to water a multi-tiered rack of
vegetating plants, a closet full of clones in dixie cups or a greenhouse of
flowering plants in 200-gallon pots. With the right design, the same system
could even do all of them at the same time!
Cons of Flow-Control
Flow-controlled systems are complex, and can be intimidating
to design and set up. There are a lot of moving pieces, a lot of connections,
and a lot of math involved in making sure everything works correctly. A small
error in the available pressure or having a few too many drippers on a line can
cripple an entire system, and troubleshooting issues can be time consuming. Not
to say that you can't learn how to do this, but it takes time. Consulting with
an irrigation professional is highly recommended when it comes to using any
drip system, especially a flow-controlled one.
Another downside of flow-controlled systems is that the
potential for user error is much larger than with their free-flow counterparts.
Sure, your dripper may emit exactly one gallon every hour, but a sufficiently
inattentive grower can still mess it up. Without a controller it can be easy to
turn the system on and forget it, leading to an unintentional flood. Things can
get out of hand even with a controller, as a small mistake during programming
could mean that your plants are getting watered for one minute three days a
week instead of one hour three days a week.
Systems with flow-control also tend to require a larger
initial capital outlay than those without flow-control. This is especially true
of automated systems, as automation options can range from a $30 hose end timer
to integrated systems costing upwards of $200,000. Individual drippers and
rolls of tubing are fairly inexpensive, but the total initial cost for a grow
with thousands of plants can be substantial.
There is one major point to be made that is an exception to
the things I've said about cost. Namely, automated, flow-controlled irrigation
systems end up saving most cultivators money in the long run. This is
especially true when compared to hand
watering. The initial cost can be high, but over the life of a system
the time savings add up considerably.
Conclusion
There is no definitive answer as to which style of system is
superior, as they both offer benefits. The lesson to take from this is to look
at what you’re trying to accomplish with your grow and pick an irrigation
system accordingly. If you’re looking for cheap and easy, your best option is
probably a DWC bucket system or a watering can. If you’re in the market for
something more sophisticated, a drip system might be a better option.
Understanding the intricacies of irrigation systems will help you pick the most
appropriate system for your grow op.
