Water & Light: Hydrophilic Physiology

Formed through and exothermic reaction that is powerful enough to launch rockets into space, the elemental combination of two hydrogens and one oxygen is the basis of all life on earth. Plants and the photosynthetic reaction are the most efficient mechanisms capable of breaking this powerful bond and providing all of us meat sacks the air we breathe.

- (Photosynthetic formula).

Before the mudskipper emerged from the muck, dinosaurs and Caribbean fireballs, before cockroach cousins and baby sharks, the world was covered with plants. Terra Verde.  We owe algae “lichenizing” with fungal and bacterial cohorts in a last-ditch effort to survive and alchemize into greater beings, a huge thanks for figuring how to capture energy from the sun, for every waking moment we have as humans.  Literally every breath.

Now that we have creatures capable of this wizardry; Let’s Mess With Them. Controlled Environmental Agriculture (CEA), is the art and science of growing plants by turning knobs, injecting solutions, and pushing all the buttons to make the very best plants possible. Whatever the growers’ definitions of quality are, they are achievable by manipulation of inputs to generate predictable and ever improving outputs. 

A Polar Molecule

Plants consist of 70-90% water. It acts as a solvent for all metabolic reactions, critical for photosynthesis and CO2 exchange, cell support and structure, and temperature regulation.

Evapotranspiration (ET) is the process of moving water against its natural propensity going from low to high, roots to leaves. Nutrients and natural compounds come into the plant’s system through this natural draw. As water migrates north in the Xylem, it carries up nutrition to deliver food to areas of new (apical, meristematic) and old growth alike.  Certain molecules are more soluble and thus mobile (N+, K+, Mg+  etc) and others are stickier and immobile (P, Ca2+ etc). This is why you see nutrient deficiencies in differing parts of plants, based on water’s ability to move them around. 

The other layer of tissue in the vascular cambium that is responsible for moving nutrients around internally is the Phloem in a process called translocation through osmosis and mass flow. Adequate amounts of water are required to keep the plants internal systems lubed up and running well. Nutrients move from areas of higher concentration to areas of lower concentration through osmosis. For example: you apply a high potassium fertilizer to the root zone and along the evapotranspiration river, K+ ions slide in on some tasty waves to head up feed your plant. Potassium, by the way, is instrumental in stomatal conductance. Without enough K+, stomata cannot maintain their turgor pressure to modulate their opening and closing. A plant may chug more water through unregulated gate cells, wreaking havoc on your crop.  With this unfettered “dieseling”, unwanted amounts of other compounds like Na+ may come in through the vacuum. Just like a diesel engine will self-destruct if parameters are not in tune, a plant will quickly run out of water in an unbalanced system.

The Holy Trinity: Water, Plants and Light

A key point to know about ET, is that it helps regulate the temperature of leaves. There is a natural gradient from cool to warm from the roots of plants to the leaves. If a canopy is overheated, it will increase the rate of transpiration. Just like and evaporative cooler mounted to a house in the Western United States or a cooling wall in a greenhouse. This is important especially when we consider the differences in “traditional” light sources i.e. HPS, CMH and LED sources. High Pressure Sodium lamps in particular have what is being referred to as “forward throw” heat in Horticultural lighting circles. Plants, especially sub-tropical fast growing annuals, grow better when they are warmed to their ideal temperature ranges. LED sources lack this output, focusing purely on delivering photons in the PAR range. The type of light you use affects the amount of water your plants will need.

In the field and under the sun, plants are bombarded with energy. Some of this falls within the PAR range, but much of it comes in the form of infrared heat energy. Think about standing on under the sun in the summertime. You metabolize and sweat to regulate temperature.  Camping in the desert gets much cooler after sunset. We have a centralized coronary system whereas plants are linear from roots to shoots. Photosynthesis in leaves is where water is drawn by hydrostatic tension and thermodynamic gradients to engage in the profound interaction known as photosynthesis. 

6CO2+6H2O🡪C6H12O6+6O2 

How sweet it is when we come into the light. Turning water and CO2 into sugar and oxygen. How we feed photons to a plant indoors directly effects how efficiently this reaction happens. Historically, growers focused on the 1000 mmol on canopy target for cannabis in flower (fast growing annual fruiting crops) for ideal return on inputs. This is an artifact of the days of growing under HPS, when delivering anything higher would also mean delivering too much infrared heat energy. You see double enders mounted 3 ft above canopy for a reason. Scorch, desiccation, and wilt will all result if they are mounted much closer. So that was it. Until now.

Modern cultivators are now seeing an ROI up to 1800 mmol on canopy (this is an arbitrary setpoint by the way and one metric that deserves an article all on it’s own: PPFD v PPF/DLI). The ability to throttle cultivation systems through precision water and nutrient delivery, optimized environmental controls are allowing for new heights, that are outpacing even the best academics in crop science. One recent Upper Midwest cultivator just shared 121 grams per square foot at over 36% THC. Call Guinness. Summertime sunshine here in Colorado approaches 3000 mmol, so I don’t think we have seen the peak yet for indoor cultivation.

You Can’t Manage What You Don’t Measure

Before this turns into an exercise in accounting, let’s think more about water’s role in Controlled Environmental Agriculture. 

Relative Humidity is relative to the temperature it’s being held in. 100 percent RH is different at 75 and 85 degrees F. The latter can hold more moisture. That’s why, when you toggle off your HPS for the night and the temp drops quickly as a result, your datalogger sees a spike and your PLC driven HVAC system has to work overtime to remove all that extra water from air that was 10 degrees cooler ten minutes ago. The same goes when you fire up those fixtures, all the dew that has set on the leaves overnight is instantly vaporized in an indoor setting. Most HVAC, without some type of predictive analytics or preset trigger time cannot handle that load and humidity can spike in a room leading to a host of problems like pest and pathogens running wild.  

LED fixtures, not putting out that water vaporizing IR, take time to warm their heatsinks and then warm the air. A much more natural gradient both for plants and Dehumidifiers at lights on and lights out. When commercial cultivators and consultants are designing systems these days, they will be presented with psychrometric charts and a hefty price tag to mitigate RH and temp to the nth degree. Failure to pay up front will mean paying on the back end. As growers get better and better at running LED, the first thing I always hear was “you were right about the dehu, I just had to hang a few more to keep up with my girls at full tilt”.

The crux of lighting and water in the air is VPD. Vapor Pressure Deficit (more accurately Vapor Pressure Gradient) is key to success in any successful indoor cultivation facility. These charts and strict adherence to them, are the difference between “meh” and “oh MAN” when a crop comes down. Log, rinse, and repeat. Once you find the sweet spot for your genetics, you can begin to tick every other input up: CO2, Nutrients, Temperature to see positive returns. You’ll want to focus on leaf canopy temperature rather than ambient. You can draw some correlations after you tweak your system but remember that plants are actively going to try and cool themselves down if overclocked. HPS canopies will run up to 7 degrees F over ambient and a well-oiled LED grow will run 2 degrees below ambient. As long as you have control over your root zone temps through irrigation, some LED rooms can run very hot and very (relatively) humid.

Now that your grow is vibrating on a higher level, it’s time to do some soul searching. You’ve found the fastest path to enlightenment. Now, you can start to think about wilding out. Herbs and tobacco will enhance their aromatic and oil properties when exposed to a little stress. This is key and the emerging science of crop steering is commonplace in state-of-the-art cultivation facilities. 

Non-Linear Equation

Keeping your crop moist and crisp or drying to the perfect moisture content is what can take A-grade to hay-grade in a matter of days. Crops like lettuce need to be high and tight all the way to the plate, and other flowering crops need to be done just right to keep the end user crisp. Water doesn’t stop working after you cut down your crop. In a sense you want to slowly assist your crop to slow metabolism down while aromatics remain intact, and metabolites ripen to their fullest potential. 

With growers, water, plants, and light; it’s all about intention. Who will be the first to apply human consciousness into their water’s molecular structure to improve crop quality? Or have some growers already released this secret by keeping the vibe high in the garden with music and mindfulness?

“The memory of life arrived on this earth carried by the soul of water. From this memory, life awoke, the human being emerged...”
― Masaru Emoto