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Testing your soil at a new location or diagnosing problems mid-grow

Regardless of how many plants you have, regular EC (electrical conductivity) and pH tests can be very revealing regarding the health of your root zone. Once a problem is evident by way of visible leaf damage, it is usually too late to rectify, especially if you are already in bloom.

Nutrients are only readily available within a certain pH range. If soil is below 7.0 it is classed as acidic soil if above 7.0 it’s alkaline.  Some plants love alkaline soils but cannabis and hemp prefer a slightly acidic soil with an ideal pH between 6.0 – 6.8.  Microbial activity is most happy within this pH range.

For a small number of plants, you can simply purchase good quality soil and some organic feeds, and you will harvest high quality buds as long as you follow the directions carefully and don’t overdo it. In such cases, you probably won’t need to send soil samples off to a lab unless you are super curious as to exactly what your purchased soil contains.

However, if you are producing large outdoor or glasshouse crops of medical cannabis you most likely won’t want to be buying large amounts of expensive soil. Instead, you should have your local soil analysed to determine how suitable it is for your project. Worst case scenario is that your soil needs lots of amendments to make it suitable for your needs, you amend it and leave it to cook* so it will be ready for your next crop.  

Preventing or Diagnosing Problems

The easiest way to check your root zone pH And EC is by collecting runoff samples and comparing the results to the input pH and EC. However, to be sure of accuracy when using this method, it is best to collect the samples immediately after you have watered each plant or immediately after an irrigation cycle. If you leave your runoff sample in a collection saucer for too long, your readings will be inaccurate due to evaporating water which will condense the runoff sample, unless collected in a sealed airtight vessel.

To achieve more precise sample data it is recommended to take soil samples, which can be soaked in distilled water, filtered and then tested.

Taking regular soil samples allows for any changes in your pH or EC to be rectified before causing any damage to your plants. Below is a simple weekly maintenance procedure you should carry out to monitor the health of your soil.

To diagnose specific plant(s) that is/are showing signs of deficiencies, just take 100g samples from the pot or grow bed of your unhappy plant(s) or as a preventative procedure, take a smaller 10g sample from multiple pots/ locations in your garden.

Each sample should be taken from a depth of approximately 6 – 8 inches!

Required items:

  • 1L Jug
  • 100g soil sample
  • 200ml Distilled Water
  • EC Meter
  • PH. Meter
  • Weighing scales


  1. Weigh out 100g of your homogenous soil sample
  2. Measure 200ml distilled or RO water ( Reverse Osmosis Filtered). Add the soil to your 200ml
  3. Strain the liquid from the soil sample using a cloth or coffee filter.
  4. Measure your pH, ideally, it should have a pH of 6.0 – 6.8  
  5. Measure your E.C, ideally, it should read between 1.0 and 2.2

Remedial Action

If your soil testing has revealed an unusual EC or pH reading, we can suggest a few simple methods to rectify the situation over a few days.

Modulating the runoff pH And EC reading by adjusting the input pH and EC values to compensate is the fastest way to bring slightly out of range soil back within desired ideals before it affects plant health.

Never allow your input pH to be lower than 5.5 or above 7.2 or you will stress the beneficial bacteria colony and exaggerate the problem you are trying to solve. You can adjust the acidity of your irrigation water/ feeds by adding;

Phosphoric acid or citric acid to decrease the pH (more acidic)


Potassium hydroxide to raise your pH (less acidic)

DayInput  pH/ECRunoff pH/ECDesired pH/ EC

It is best to monitor the runoff values daily for a few consecutive days while carrying out a corrective pH/EC irrigation cycle. DO NOT adjust inputs each day.

The same methodology applies to high EC /pH and vice versa: you are simply diluting excess EC with reduced EC inputs, or if you are seeing low EC runoff, feed with stage specific feeds at slightly higher EC than your readings to gradually increase EC to desired levels.

For 100% fully organic systems, you can use compost teas inoculated with beneficial bacteria, which over the coming days will digest more of your soil making more nutrients available to your plants.

If the above methods do not adjust the soil pH or EC readings back into ideal ranges, you could have an unbalanced soil mix which will require pH regulator dry inputs such as Sulphur or agricultural lime.

Professional Lab analysis

If you need an in-depth analysis of your soil or to further diagnose problem plants in your garden follow the below sampling procedure and send your sample(s) off to your local soil testing facility along with a report regarding location and intended crop.


  1. Simply collect many small samples of approximately 10 grams each from various locations around your chosen cultivation site or from multiple pots.
  2. Combine all your samples and mix them well, place them in 1 bag and shake vigorously until fully blended.
  3. If you are sending this off to a lab for testing it’s best to ask them for their standard procedure regarding sample size and best way to package it. In some cases they will send you special containers that compacts your soil sample into a known volume.  
  4. Send off your sample and wait for your results.

Once you receive your soil analysis, it will usually include a report with suggestions as to what can be added to improve it. If your soil is not ideal and requires significant amendments to be added, especially if you are required to increase the organic content and it will need to be rested until next season, to speed up the process you should inoculate with microbes.

Supercharging Your Soil  

If you add microbes to your amended soil mix you can greatly decrease the time until ready for use. We recommend adding compost teas to your mix to rehydrate after amendments instead of plain water. The best way to apply inoculants is adding them to a compost tea and bubble this for a couple of days prior to adding to your soil mix.


To make up 10 litres of Microbe tea:

  1. Add 8L of distilled, rain or tap water bubbled for 24 hours to remove the chlorine to a suitable container
  2. Add 2L of Black Strap Molasses (unsulphured)
  3. Add 200g of innoculant (available online). TNC produce  a powdered product called MycorrMax, which contains: Endomycorrhizal (8sp), Ectomycorrhizal (7sp), Trichoderma ( 5Sp), Bacillus (13sp), alongside Humic Acid, Amino Acids, Vitamins, Natural Plant Growth Hormones and vitamins derived from natural marine algae ( Ascophylum Nodosum) which are an excellent food source for microbes
  4. Add an airstone connected to an aquarium air pump and bubble for 24 hours minimum
  5. Add 1L for every litre of soil mix

Leave composting protected from the rain until next season, if possible turn the compost pile once each month. Next season your will have a beautiful living soil.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

This post is also available in: French