The pH scale, from 1 to 14 measures acid-to-alkaline balance, 1 is the most acidic, 7 is neutral, and 14 most alkeline. Every full point change in pH signifies a ten-fold increase or decrease in acidity or alkelinity. For example, soil or water with a pH of 5 is 10 times more acidic than water or soil with a pH of 6. Water with a pH of 5 is one hundred times more acidic than a water with pH of 7. With a ten-fold difference between each point on the scale, accurate measurement and control is essential to a strong, healthy garden.

Cannabis grows best in soil with a pH from 6.5 to 7.0. Within this range Cannabis can properly absorb and process available nutrients most efficiently. If the pH is too low (acidic), acid salts chemically bind nutrients, and the roots are unable to absorb them. An alkaline soil with a high pH causes nutrients to become unavailable. Toxic salt build up that limits water intake by roots also becomes a problem. Hydroponic solutions perform best in a pH range a little lower han soil. The ideal pH range for hydroponics is from 5.8 -6.8. Some growers run the pH at lower levels and report no problems with nutrient uptake. The pH of organic soil mixes is very important because it dictates the ability of specific pH-sensitive bacteria.



Measure the pH with a soil test kit, litmus paper, or electronic pH tester, all of which are available at most nurseries. When testing pH, take 2 or 3 samples and follow instructions supplied by the manufactuer "to the letter." Soil test kits measure the soil pH ans primary nutrient content by mixing the soil with a chemical solution and comparing that solution to a chart. Every one of these kits I have seen or used is difficult for novice gardeners to acheive accurate measurements. Comparing the color of the soil/chemical mix to the chart is often confusing. If you use one of these kits, make sure to buy one with easy to use directions and ask the sales clerk on recommendations on using it.

If using litmus paper, collect samples that demonstrate an average of the soil. Place the samples in a clean jar, and moisten the samples with distilled water. Place 2 pieces of litmus paper in the muddy water. Afer 10 seconds, remove 1 of the strips, wait a minute before removing the other one. Both pieces should register the same color. The litmus paper container should have a pH color chart on the side. Match the color of the litmus paper to the chart to get a pH reading. Litmus paper will accurately measure the acidity of the substance to within a point. The pH readings will not be accurate if altered by water with a high or low pH, and the litmus paper couls give a false reading if the fertilizer contains a color tracing agent.

Electronic pH testers are economical and convenient. Less expensive pH meters are accurate enough for casual use. More expensive models are quite accurate. Pay special attention to the soil moisture when taking a pH test with an electronic meter. The meters measure the electrical current between 2 probes and are designed to work in moist soil. If the soil is too dry, the probes do not give an accurate reading. Perpetual pH-metering devices are also available and are most often used to moniter hydroponc nutrient solutions. For accurate pH test with an electronic pH meter:
-Clean the probes of the meter after each test and wipe away any corrosion.
-Pack the soil around the probe.
-Water soil with distilled or neutral pH water before testing.

Check the pH of irrigation water. In dry climates, such as the desert, Austrailia, et cetera, irigation water is often alkeline with a pH above 6.0. The water in rainy climates is often acidic with a pH below 6.0. After repeated watering, water with pH that is too high or too low will change the growing medium, especially in organic ammended soils. Raw-water pH above 6.0 helps keep fertilizer mixes from becoming too acidic. Climate conditions can also affect irrigation water pH. Check the pH atleast once a week.

Cannabis will grow in almost any soil, but it flourishes when the pH is between 6.5 and 7.0. Commercial potting soil almost never has a pH above 7.5. A lower pH is more common, even as low as 5.5. Some potting soils purchasedat a nursery are pH balanced and near a neutral 7. However, most potting soils have a tendency to be acidic. The easiest way to stabilize soil pH is to mix in 1 cup of Fine Dolomite Lime per cubic foot (.25 liters) of potting soil. Mix Dolomite Lime thoroughly into dry soil. Remix the soil in the container after it has been watered.

Fine Dolomite Lime has long been a favorit pH stabilizer for gardens. It is difficult to apply too much as long as it is thoroughly mixed into the soil. Dolomite has a neutral pH of 7, and can never raise the pH above 7. It stabalizes the pH safely. Compensate for acidic soil by mixing dolomite with soil before planting. Dolomite is a compound og Mg and Ca. Dolomite does not prevent toxic salt accumulation caused by impure water and fertilizer build-up. Proper fertilizer and regular leaching helps flush away toxic salts. When purchasing look for Dolomite Flour, the finest fast-acting dust-like grade available. Coarse Dolomite could take a year or more before it becomes available for uptake by roots. Improperly mixed dolomite will stratify, forming a cake or layer that burns roots and repels water.

Hydrated Lime contains only Ca and no Mg and alters pH quickly. Mix thoroughly with warm water and apply with each watering for fast results. Many growers use a mix of .25 cup hydrated lime and .75 cup dolomite lime. Do not use more than .5 cup hydrated lime per cubic foot of soil or it can toxify the soil from fast release and kill the plants.Hydrated lime is also used as a grow room fungicide. Sprinkle it on the floor and around the room to kill fungus on contact.

Do not use quicklime; it is toxic to plants.

Hydroponic pH:

The pH of the nutrient solution controls the availability of ions that Cannabis needs to assimilate. It grows well hydroponically between a pH of 5.5 - 6.5, with 5.8 - 6.0 being ideal. The pH in hydroponic gardens requies a vigilant eye.

Roots take in nutrients at differnet rates, which causes the ratios of nutrients in the solution to change the pH. When the pH is above 7 or below 5.5, some nutrients are not absorbed as fast as possible. Check the pH every day or 2 to make sure it is at the perfect level.

Deviations in pH levels often affect element solubility. Vlues change slightly with different plants, grow mediums, and hydroponic systems. Overall, hydroponic gardens require lower pH levels than soil. The best pH range is from 5.5 - 6.5. Different mediums perform best at different pH levels. Follow manufactuer guidelines for pH level, and correct the pH using the manufactuers' suggested chemicals because they will rect best with their fertilizer.

The pH can easily fluctuate up and down one full point in gydroponic systems and cause little or no problem with nutrient uptake.

Follow the directions on the container, and remember to mix adjusters into the resivior slowly and completly; all of it. Fertilizers are normally acidic and lower the pH of the nutrient solution. But nutrient solution is still taken in by plants, and watertranspires and evaporates into the air, which causes the pH to climb. Stabalize the pH of the water before adding fertilizer. Make a correction if readings vary ± one-half point.

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Page last modified on Wednesday May 15, 2013 12:47:46 CEST by admin. (Version 4)