Why is alkalinity important for growing quality cannabis?
When I speak with growers about water quality, one of the first information they share with me is the pH of their water source. Micronutrient availability is influenced by the pH of your substrate or root zone, with micronutrients being more available at lower pHs and less available as pH rises. When it comes to water quality, however, I’m more concerned with the alkalinity of their source than than the pH. Alkalinity is a measure of water’s ability to neutralize acid and is made up of carbonates and bicarbonates dissolved in it.
What is alkalinity?
Alkalinity can be compared to liquid limestone, which is an excellent analogy. When you water, the carbonate and bicarbonate dissolve in the soil and have the same effect as the limestone in your growing media in terms of boosting pH and resisting acidification. Alkalinity is measured in milliequivalents per liter (meq/L) or milligrams per liter (mg/L), thus you’ll encounter either of these units when it’s mentioned. Fortunately, converting between these quantities is simple: one meq/L equals 50 mg/L.
How much alkalinity do you require now that you understand what it is and how it is measured? Or, in other words, how much is too much? This is dependent on the crop you’re producing, as well as the species, container size, and crop period. Water with a higher alkalinity can be used to produce crops that prefer a higher pH, larger containers, and longer crop times. Species that thrive in lower pH environments, smaller containers, and short yields, on the other hand, require lower alkalinity.
While we can’t go into detail about species differences in this article, plants that prefer a higher pH will accept more alkalinity since the pH will drift up, whereas plants that prefer a lower pH will be less tolerant of alkalinity due to pH drift. Plants in packs and flats tolerate a little more alkalinity, up to 1.7 to 2.0 meq/L (85 to 100 mg/L), depending on the flat size. Plugs grown in small cells require water with 0.75 to 1.25 meq/L (40 to 60 mg/L), while plants in packs and flats tolerate a little more alkalinity, up to 1.7 to 2.0 meq/L (85 to 100 mg/L). Because the lime charge in the substrate is used up in longer crop times, plants grown in containers greater than or equal to 6 inches can tolerate up to 2.5 meq/L (125 mg/L) alkalinity.
How to test alkalinity in cannabis?
There are a number different ways to measure alkalinity, and they differ in terms of accessibility, accuracy, and cost. Alkalinity test strip kits, which may be purchased at pool and spa supply stores, are the simplest way. Simply take a sample of your water, dip the test strip in, and wait for the strip’s color to tell the approximate alkalinity concentration. While this is a very rapid and inexpensive way to measure alkalinity, the result will be an estimate of the concentration. A titration kit can be used in a similar way, in which reagent is introduced to the water sample to turn it color, then acid is added until the color changes, with the number of drops added indicating the alkalinity range.
Alkalinity test kits, which are often used for aquariums, can also be used for greenhouse water for a more accurate reading. Your water sample is mixed with a reagent, and the vial is placed in a colorimeter, which measures the color and calculates the alkalinity content. These devices are more accurate than test strip kits or basic titrations, and they cost less than $100. The most accurate technique to test alkalinity is to send a sample to a commercial lab for analysis, but this will cost more and take a little longer than using in-house procedures. One of the best alkalinity meters is the Hanna Instrument HI775 Freshwater Alkalinity Checker Test Kit – Freshwater Aquariums.
How to fix high alkalinity?
If your water has a high alkalinity level, you should also examine the hardness of the water. The term “hardness” refers to a combination of calcium and magnesium measurements. These two mineral nutrients are both secondary macronutrients that plants require, but they have an antagonistic connection, and too much of one can prevent the other from being absorbed.
Although alkalinity is a crucial part of water quality, it does not always receive the attention it deserves. You may measure the alkalinity in your water, evaluate how it affects your crop culture, and investigate strategies to improve the quality of your water using the information in this page.
Optimal alkalinity for cannabis?
For most greenhouse-grown crops, including cannabis, a target endpoint alkalinity of roughly 2 milliequivalent (meq) [122 ppm bicarbonate (HCO3-)] is recommended. (This also applies to indoor cannabis produced in containers.) The end result should be a pH of 6.0 to 6.2 in the water.