Parts Per Million or PPM is a standard measurement of residual solvents. It is also used to measure the the presence of mold or other pesticides. In cannabis cultivation, it refers more precisely to the concentration of total dissolved solids in the water that is provided to the plants. This measurement approach makes it easier for growers to understand exactly how many minerals and substances are in the water.
Plants are only able to take in so many different minerals at a time, and obtaining this information can avoid overindulgence that could have negative consequences on plant growth. One part per million is equal to 1 mg of solubles per litre of water, and this is a very small amount to measure.
For drinking water, bottled water or reverse osmosis is measured as low as 0 parts per million, and tap water is sometimes tested as high as 700 parts per million, but most of the tap water is between 200ppm and 400ppm. A tool called A TDS meter is available to calculate ppm. Water TDS is expressed in ppm, but most people only use ppm to cover both terms. The ppm range shouldn’t matter too much for a meter. In the field of cannabis cultivation, meters above 3500ppm are relatively rare.
Many growers will never even have to worry about buying a TDS meter, but if you’re dealing with issues such as overfeeding the seeds, it’s a nice addition. A TDS meter typically costs around $25 and it’s nice to know what ppm range your water is in so that you can adjust the nutrient levels accordingly. For new cannabis seedlings, ppm should be around 100-250. By the time it gets to the second half of the flowering cycle, ppm levels should be reaching up to 1000-1600.
Use of Term
The PPM in my soil is perfect for cannabis cultivation.