Soilless Medium & pH Relationship

Soilless Medium & pH Relationship

This article will represent the relationship between soilless growing medium and pH balancing. There are multiple factors that reflect the over all medium pH; such as, the nutrient mix solubility to dissociate or ionize into hydrogen ions (H+) and associated anions. The pH scale is complex to understand rather than being characterized by simple numerical values or color rendering charts. Below are some contributing factors and ways to properly measure your soilless growing medium.

Understanding the pH Scale

pH scale with ion count
Look at the amount of hydrogen ions or anions. This will help you understand that the pH scale is not as simple as 14 numerical places with 0 being representing 15 measurable spots.

Well understanding the pH scale is simple the actual band of pH values are highly over looked. There are several definitions of pH. The most common definition of pH is potential hydrogen. Therefore, one can distinguish the pH scale by the potential of ions (H+)  or anions H-. The amount of acid present will determine the strength by acidity; therefor, ionization. The more ionization happens the lower the numerical pH scale becomes. Another way to understand is by the application of fertilizers.

When applying nutrients to your water, your mixing an acid, by concentration for its nutrient strength. The more nutrients added to your water, the more acidic it will become. Your pH scale ranges for 0-14; in which 0 is absolute acid, 7 is neutral and 14 being absolute basic. Between each pH number you can measure in tenth of a decimal. This measurement means there is not 15 measurements of the pH scale but 15 X 10= 150 points of measurement for pH. Even more precises is measuring by double digits.

For Example) A 6.4pH is 10x more acidic than 6.5pH. Broken down the pH scale would look like this: 6.41, 6.42, 6.43, 6.44, 6.45 til 6.5pH is reached.  This is important for growers to understand as it allows them to maintain accuracy and monitor minor pH swings in real-time. Monitoring in real-time can be accomplish by instruments for sale.


Measuring Soilless pH Value

A high quality pH pen is required to accurately measure your nutrient pH, as well as, your growing medium pH. A pH meter measures the hydrogen-ion activity in water or nutrient based solutions, indicating its acidity or alkalinity. The numbers express with represent where the solutions pH range falls on the scale.

Amazon pH pen
Low quality pH pen. The pen was bought on Amazon that can read double digits. The probe did not last long and requires frequent calibrations. Do not buy!
How to calibrate your pH pen healthy cannabis review
This is a high quality pH pen with simple self calibration functions. Calibrations can be single or double points. The pH probe is replaceable and is very accurate. This pH pen is worth the investment and is comparable to Blue Labs pH meter.










Measuring the soilless medium the correct way is important. The typical grower would usually test the pH run off. This is effective for a general summery but is not effective at telling the true medium pH value. To do so you must test the actual soilless growing medium. Please note, you should use a quality pH meter such as a “potentiometric pH meter”. Ideally Follow the step by step instructions below

  1. Gather a representative sample of your medium. The sample should be accurate to your medium not an area on the top with signs of salt.
  2. Air dry the sample for several days. The sample should be spreed thin for even drying.
  3. Place the sample in cheese cloth and soak your test sample with distilled water. The water should be room temperature.
  4. Soak for approx 1 hour and remove the test sample.
  5. Test with your digital pH meter. The sample water must be stirred for accurate reading. The meter may take approx 2 minutes to find the true value. Wait til the pH meter does not read a new pH reading for approx 5 seconds. This will allow your test result to be accurate withing 0.01pH value.

Complex pH Relationships

Your determining pH factor is based on several variables. The variables include your initial water pH, nutrients strength, water temperature(influence of O2 molecules), current soilless pH value, as well as, the actually solubility of your nutrients and tap water. All of these variables need to be balanced to minimize pH swings and for a optimum growing environment. It is best to water consistently with the desirable pH.

Example of complex pH relationship

Your soilless medium generally consist about 65-75% peat moss of the total growing medium. Peat moss is acidic in nature therefore contributing to your total ionization. When adding nutrient’s to the medium what is the ability for the medium to buffer and therefor stable? Most soilless mediums have a buffer such as 10% dolomite. Each bit of medium will battle a electrical charge to become acid or alkaline. The more balanced your medium is and with consistency nutrient pH the less probability of a pH swing.

The pH swing is more common with hydroponic growers because there initial buffer is your H2O solution. The best way to keep your H2O solution as a buffer is having a water reservoir with balanced pH water available for automatic top ups. As a soilless grower, your buffer is your medium not your water. Keeping your medium balanced is the key to success for nutrient absorption.

Various other growing mediums such as rockwall and coco require pre-soaking to help balance the medium before planting. This is a perfect example why choosing your growing style and medium is important to success. A lot will depending on your knowledge and ability to understand the growing system and overall your cannabis strain requirements.

Ideal pH Value for Soilless Medium

The ideal pH value for soilless medium is between 6.2pH to 6.5pH. This range is designed by most soilless companies for a stabled buffered pH range. The range will swing with non pH nutrients and water. The ideal range for cannabis growing in soilless medium is a 6.4pH in vegetation and 6.2pH in flower.

Soil pH Scale Chart

pH nutreint scale for cannabis

Chart Review:

The chart above demonstrates the best pH for soil growing as apposed to a soilless growing. Below is the soilless grow chart for nutrient uptake ability. Cannabis do like slightly acid growing environment, your pH range should not drop below 6.0pH or higher than 6.5pH. As you review the chart phosphorous becomes nearly unavailable below 6.0pH. Phosphorous is very important to cannabis plants for many every day activities as well as a primary nutrient for bud building. You can review this article for more information about nutrient feed charts as well as cannabis nutrient guidelines & deficiency.

Soilless pH Scale Chart

The chart above demonstrates the best pH for soil growing as apposed to a soilless grow chart. As you can see this chart displays the best pH for nutrients and soilless growing. Why this is important compared to the soil chart is the active particle charge of the growing medium. Soil has many possible pH influences such as clay, peat moss, sand, organics, hard metals and manure. Were as, soilless is a baked medium, designed for indoor growing. The soilless medium consist primarily of 65-75% peat moss, dolomite, perlite, wetting agent and possible mycorrhizae.

The best pH range for soilless growing medium is 6.0-6.5pH with the ideal pH being 6.2-6.4pH. This holds particularly true for cannabis cultivation. As cannabis is characterized as liking acidic growing environment is a over generalization. Cannabis like only slightly acidic environments.

The main difference between cannabis growing for soilless, soil or hydroponics is not only by definition of growing styles but by pH nutrient availability. To compare the three is not that simple as you can have combinations of hydro and soilless systems. Each will obtain their own ideal pH balance. Our focus is on soilless growing as perhaps the most common growing method because of its simplicity and cost effectiveness. Soilless is also the most forgiving as it has the ability to help buffer the pH resulting in less dramatic pH swings.



Final Though

Weather your growing in soilless, soil, hydroponics or a hydroponic hybred system, only one major pH factor remains: each grow style will require a different pH range for nutrient availability. You cannot determine the pH range simply by the assumption of growing in any acid environment as cations and ions are always battling. Also the environment plays a significant role in how your plants will use your nutrients.  Simple vapor deficit will cause the plant to use more or less water depending on temperature and relative humidity. Thus, increasing or decreasing the nutrients in your medium. Your key to success is to understand the pH scale as a wide range of possibility and not limited to a simple 15 numerical scale. Investing in a quality pH meter as well as regular maintenance plays a key role to your success. Please review calibrating your pH pen & maintenance for more in-depth information.

Happy Growing

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