Just Add Salt

Columns - Hort How-To

Maximize yield by satisfying your plants' ionic needs in different phases.

Hand fertilization is one of the biggest sources for errors and variations in cultivation. Adding a fertigation delivery system is a key tool for producing consistent results.
© Roxana Gonzalez | iStockphoto

Cannabis growers across the globe grow their plants in salt water. In fact, every plant in the world grows in salt water, and has been doing so since the day they came ashore.

It is not “ocean” water in which these cultivators grow their cannabis, but it is indeed very salty water that plants adore. In the field, rain falls and percolates down through the soil, dissolving minerals (mostly salts) that it encounters. Salts occur naturally, and the salt level in soil determines how much nutrient value the soil contains. Some salts are good, and some not so good, but the good ones are the key to plant growth and profit.

When dissolved in water, salts like calcium nitrate “disappear" into solution as the calcium atom and nitrate molecule are being pulled away from each other—transforming the dry, uncharged salt into one positively charged calcium atom (Ca++) and two negatively charged nitrate anions (NO3).

The uptake of these charged atoms and molecules has produced some interesting adaptations in plants, such the ability to pump potassium into the plant. Once nutrients have been absorbed, biology happens, resulting in plant biomass, which after harvest and drying, consists entirely of the nutrients it absorbed in its life.

To get more nutrients absorbed, we need to be pouring more salt water onto our plants.

Get Wet

Getting our salt water to have the proper nutrient levels begins with source water. For the cost of an irrigation-suitability test from the local soil and water agriculture lab, growers can learn everything they need to know to start building nutrient recipes that are compatible with their water.

Our water preferences are, in order: well, municipal and reverse osmosis (RO). While RO may be a required treatment for some sources, it comes last on our list primarily because of its expense. Agricultural well water in the U.S. commonly has so much dissolved calcium and magnesium that many mainstream fertilizers were designed to depend on the water for calcium and magnesium.

Well water also typically contains high levels of HCO3- (bicarbonate) ions that raise pH over time. Bicarbonate ions are measured by Total Dissolved Solids (TDS) and Electrical Conductivity (EC) meters, along with nutrients. A lab is required to isolate the two to find out how many bicarbonates there are. That measurement describes the level of alkalinity of the water, which in turn, tells us how fast it can raise pH. This is chemistry, so there is math that allows calculation of the amount of acid required to neutralize enough bicarbonates to reduce pH to desired levels. To experiment, simply measure and record pH of your source water while adding incremental amounts of acid to find out exactly how much to add per gallon to get to any desired pH. (Editor’s note: For more information on pH management, see the Hort How-to column in Cannabis Business Times’ July/August 2016 issue.)

Municipal water sources have bicarbonates, but at levels much lower than well water, and they do not exert any significant pressure on the water pH. Municipal sources also typically contain moderate to low levels of calcium and magnesium that require supplementation for most formulations.

Salty Enough for You?

We now turn to the task of really making the water salty so that it satisfies the plant’s needs in different phases. This has been done for pre-mixed products, which are the simplest source of effective hydroponic nutrients. Their performance is difficult to improve on. If a little complexity is tolerable, dive into DIY water-soluble nutrient salts.

Calcium and potassium nitrates, ammonium, potassium and magnesium sulfates, and mono potassium phosphate (aka MKP) are six water-soluble nutrient salts that deliver major nutrients and yield, which allow growers to design fertilization recipes for a wide range of water types and growing situations. The amount of major salts growers will use is dependent mainly on their source water.

Well water is the columnists' first choice when it comes to choosing an H2O source for building a cannabis nutrient recipe.
© FirstClickJeremy | Thinkstock

The three major nutrients Nitrogen (N), Phosphorus (P) and Potassium (K) control overall growth rate. Adding or withholding any of these three has a dramatic effect on plant growth, so controlling their levels gives the grower pretty much total control over plant growth, allowing them to match their nutrient delivery to the needs of their specific operation. Add to that control salt costs around $1.25 per pound in low volumes. With somewhere around 8 grams of these salts required per gallon of dilute nutrient solution, one 300-lb. set of 25/50-lb. bags of these salts can make 17,000 gallons of dilute solution that will eventually become 300 lbs. of cannabis biomass.

Water-soluble fertilizers are created and ruled by physics and chemistry, and that means no guessing is necessary. We like that, and so should every grower reading this. A gram of calcium nitrate salt in 1 gallon of water delivers 31 ppm of nitrate nitrogen and 45 ppm of calcium, guaranteed! Add another gram and double those numbers. All water-soluble salts have this predictable character, which eliminates all guessing about what the plants are getting. All that is necessary to access these nutrients is a little math.

Designing a nutrient program from these individual salts is a simple matter with the help of any number of available nutrient calculator tools. You can do the math by hand—but don’t. We can recommend HydroBuddy, an open source hydroponic nutrient calculator available online from Dr. Daniel Fernandez, or you can access a copy of Otoké’s spreadsheet-based calculator built from data provided by HydroBuddy at: bit.ly/OtokeNutrientCalculator.

Calculator in hand, all that remains is to choose some target nutrient levels, throw in the right amount of salt and get to mixing. What a plant responds to throughout a plant’s lifetime is pretty well known from mainstream horticulture. NPK targets that we start growers with for veg and transition are 150 ppm N, 50 ppm P, 200 ppm K and 200 ppm Ca. Starting flower formulas are 150 ppm N, 150 ppm P and 450 ppm K. Sulfur is generally not considered in the formulations unless there is none or a whole lot in the final formula. A calculator makes it easy to learn how to assemble the salts into different formulations using the same basic process that fertilizer manufacturers follow. You don’t need to become a nutrient guru, but with this system, you can.

Just Water Evenly

“Just water evenly” is what we have heard given for instruction to the newbie in the grow. How hard can it be? The answer is it can be darn hard, and hydroponics offers much better control over nutrient delivery than a rookie on an iPhone.

Hand fertilization is one of the biggest sources for errors and variations in cultivation. Adding a fertigation delivery system is a key tool for producing consistent results. Delivery of nutrient solutions is not a high-tech problem, but technology and a little math can further simplify a grower’s life, as well as give them more flexibility. This is the one bit of automation every grower should have. Systems are scalable from hobby to field, so there is little excuse for watering or nutrient delivery problems.

Simple fertigation systems draw from tanks filled with dilute nutrient solutions ready for application. If there are different nutrient recipes, there must be different tanks. Just like pre-mixed A/B products, A/B systems use less floor space by mixing salts together at 100 to 200 times the dilute concentration and using injectors to mix the concentrated nutrients with the appropriate amount of source water to give the desired dilute concentrations of nutrients at the drip emitter.

Still, a grower needs separate A/B tank sets for each recipe. The most compact system is a single salt dosing system where concentrated solutions of individual salts are re-injected into the supply water at a rate calculated to deliver the exact nutrient profile. What sells growers on one single salt dosing is that any fertilizer recipe can be delivered to the plants whether they are in veg or flower. For growers who want to use different recipes for different strains, single salt dosing is the solution.

With controller and injector technology, implementation is quite simple.

About the Authors: Kerrie and Kurt Badertscher are co-owners of Otoké Horticulture LLC (OtokeHort.com), and authors of “Cannabis for Capitalists.” They have worked with large-scale cannabis producers for more than 5 years. Kerrie has been involved with plants her entire lifetime and earned certification as a Professional Horticulturalist by the 100-year-old American Society for Horticulture Sciences. Kurt brings his 34 years of corporate experience and operations management skills to bear on the business challenges of cannabis cultivation.