Many new growers get into trouble with pH balance in their gardens. Anything that is done to the soil medium effects its' balance. The most important by far is water quality. It is common to have water that is slightly above or below a neutral pH. This is not a bad thing, but one must be careful to know the quality of your water and have an understanding of how to achieve a good balance.
The numbers used to describe pH are not of any specific unit, but are only a commonly recognized description of the far more complicated processes in play.
scale, from 1 to 14 measures acid-to-alkaline balance, 1 is the most acidic, 7 is neutral, and 14 most alkaline. Cannabis grows best in soil with a pH from 6.5 to 7.0
. [plant] Within this range Cannabis can absorb and process available nutrients most efficiently.
Nutrient uptake is the process of the roots absorbing the nutrients provided to the plant.
Every full point change in pH signifies a ten-fold increase or decrease in acidity or alkalinity. For example:
soil or water with a pH of 5, is 10 times more acidic than water or soil with a pH of 6. (10¹=10 where ¹ is the point in the pH scale)
Water with a pH of 5 is one hundred times more acidic than water with pH of 7. (10²=100 where ² is for each point on the pH scale)
If the pH is too low (acidic), acid salts chemically bind (tie up) nutrients, and the roots are unable to absorb them through nutrient uptake.
An alkaline soil with a high pH also causes nutrients to become unavailable.
Having the pH too far out of the usable range can cause toxic salt build up that limits water and nutrient intake by roots.
Not all growing systems are the same. There not only are differences between optimum hydroponic pH and soil pH, but also slight differences between nutrient and fertilizer manufacturers.
Hydroponic solutions perform best in a pH range a little lower than 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. This is usually due to the manufacturing process used to generate the nutrients and the buffers or chelation elements used. Buffers are compounds that act to resist a change in pH. Chelation act to resist the breakdown of certain nutrient elements that would otherwise react with other elements in the nutrient mix.
The pH of organic soil mixes is very important because it dictates the ability of specific pH-sensitive bacteria to break down organic compounds into forms that the plants can use. Fertilizer does not feed the plants, contrary to common perception. They feed the soil and provide the needed building blocks that the bacteria use to create the nutrients that the plants require.
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 manufacturer "to the letter." Soil test kits measure the soil pH and 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 achieve 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.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 (continuous without interruption) pH-metering devices are also available and are most often used to monitor hydroponic 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.
If using litmus paper
, collect good samples of the soil, then place the samples in a clean jar, and moisten the samples with distilled water. Place 2 pieces of litmus paper in the muddy water and wait 10 seconds, then remove 1 of the strips. Wait one 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
Litmus paper will accurately measure the acidity of the substance to within a point. Note that pH readings will not be accurate if altered by water with a high or low pH, and the litmus paper could give a false reading if the fertilizer contains a color tracing agent.
Check the pH of irrigation water
. In dry climates, such as the desert, Australia, Arizona, etc., irrigation water is often alkaline 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 chemistry balance of the growing medium, especially in organic or amended 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 at least 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 purchased at 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 (28 litres) 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 favourite 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 stabilizes the pH safely.
Compensate for acidic soil by mixing dolomite with soil before planting. Dolomite is a compound of Mg (Magnesium) and Ca (Calcium). Dolomite does not prevent toxic salt build-up caused by impure water and fertilizer build-up. Proper fertilizer and regular leaching (To remove soluble or other constituents from by the action of running water through the medium (soil makeup)) 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; just sprinkle it on the floor and around the room to kill fungus on contact.Do not use quicklime; it is toxic to plants.If you find that you have damaged the pH balance of the soil you are growing in it is far better to mix up a fresh batch of soil and transplant rather than trying to compensate after the fact. It is possible, but it's difficult and quite hard on the 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 requires a vigilant eye.
Roots take in nutrients at different rates, which cause 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's at the perfect level.
Deviations in pH levels often affect element solubility. Values 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 manufacturer guidelines for pH level, and correct the pH using the manufactures’ suggested chemicals because they will react best with their fertilizer.
The pH can easily fluctuate up and down one full point in hydroponic systems and cause little or no problem with nutrient uptake.
Follow the directions on the container, and remember to mix adjusters into the reservoir slowly and completely; 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 water transpires and evaporates into the air, which causes the pH to climb. Always add your nutrients before you stabilize the pH. Make your corrections slowly. You need to use as little adjustment solution as possible to correct the imbalances.
It is far better to have the pH off a little bit than adjusting too far and having to adjust back. The acids or alkalis that are used to make these adjustments can damage the chelation of the nutrient formulation and cause some of the elements to become unavailable. It takes some time for the adjusting substances to do their job so wait at least an hour, sometimes up to a day to allow the chemistry to happen before you make more adjustments.
Taking the time to properly observe your environment and learning the processes that are taken to create it and make it flourish. Slow and steady wins the race. [rasta]