Definition - What does Litmus Paper mean?
Litmus paper is used in chemistry and by plant growers to determine whether a substance is acidic, alkaline, or neutral. Growers of cannabis may test their soil, hydroponic nutrient solution, or any growing media by using litmus paper to assess their pH levels, and see where it falls on the pH scale.
Blue litmus paper turns red when exposed to acidic media, red litmus paper turns blue when exposed to alkaline media, and a neutral pH will result in purple paper. The ideal pH for cannabis is moderately to slightly acidic, generally between 5.5 and 6.5, meaning when a cannabis grower tests their media using litmus paper, they want to see blue paper turn red.
Hydrolife explains Litmus Paper
The pH scale is exponential. Each number runs from 0 to 14 (though there can be readings higher or lower), with seven being neutral. Anything lower than 7 is considered more acidic than neutral, and everything exceeding 7 is more alkaline.
pH is an important indicator used to determine how strong a nutrient solution is. Many growers test their pH levels regularly throughout a grow cycle, as pH levels fluctuate as plants grow and use up more and more nutrients and water.
The usefulness of litmus paper in determining pH when growing cannabis is limited. A pH meter is more useful when a precise reading is wanted. Along with pH testing equipment, no matter how high-tech, cannabis growers should also have on hand a means to alter their pH levels. This can be done with 'pH Up' and 'pH Down' products, or a number of household ingredients.
Litmus testing has been used by plant growers for thousands of years. Extracts from lichen are used to create the dyes, which react with a solution to turn either blue, red, or purple. Of course, this method has limitations, especially for users who are color blind, or who otherwise have vision problems. Also, the paper can't pinpoint exact pH levels; it can only come close.