pH Value and Nutrient Uptake in Cannabis: Why a Well-Nourished Plant Can Still Starve

The young leaves become lighter. The green color disappears between the leaf veins. Spots develop on older leaves. Growth slows down.

Regular fertilization was being applied. There should have been more than enough nutrients in the substrate.

Many growers now reach for the next bottle. More CalMag. More grow fertilizer. More bloom fertilizer. Perhaps another booster as well.

This is exactly where the real problem often begins.

A cannabis plant can be surrounded by nutrients and still show deficiency symptoms. Not because the pot is empty, but because the conditions in the root zone do not support nutrient uptake.

pH plays an important role in this. However, it is only one part of the system.

pH does not show how many nutrients are present. It influences the form in which they exist and how effectively roots, water and microorganisms can work with them.

Anyone who views pH only as a number on a meter therefore overlooks the most important point.

The plant does not grow in the watering can. It grows in the root zone.

The most important points first

• The pH of the irrigation water is only an input value.
• The decisive conditions are those directly around the roots.
• Soil, Living Soil, coco and hydro require different working ranges.
• pH lockout is not a sudden on-and-off switch for nutrient uptake.
• The water’s acid-neutralizing capacity is often more important than its initial pH.
• pH, EC, irrigation practices and root health must be considered together.
• MicroBio+ can be used as a natural pH-down. Its effect depends on the water’s buffering capacity.

What pH really measures

pH describes the activity of hydrogen ions in a solution.

A value below pH 7 is considered acidic. A value above pH 7 is considered basic. Under usual conditions, pH 7 is considered neutral.

The logarithmic scale is important here.

The difference between pH 7 and pH 6 is not simply a small step. At pH 6, hydrogen ion activity is approximately ten times higher than at pH 7. The difference between pH 7 and pH 5 is already approximately a factor of 100.

Nevertheless, a deviation of 0.1 or 0.2 pH units does not automatically mean that a grow becomes unbalanced.

Cannabis does not require one single magical pH value. It requires a functioning range.

The crucial difference: irrigation water is not the root zone

Several pH values can exist simultaneously in a grow:

• the pH of the source water
• the pH of the finished nutrient solution
• the pH of the substrate solution
• the local pH directly at the root
• the pH of the drain or runoff

These values do not have to be identical.

A nutrient solution can enter the pot at pH 6.2. A different value may prevail in the upper substrate area than at the bottom of the pot. Directly at an active root, the pH may differ again.

This is because a root zone is not a static container.

Roots absorb positively and negatively charged nutrient ions. To maintain their electrical balance, they release hydrogen ions or other charged compounds, among other substances. Root exudates, microorganisms and chemical reactions also alter the environment in the immediate vicinity of the root.

The watering can provides the input value. The root zone determines the result.

What pH is right for cannabis?

The following values are practical working ranges. They are not fixed boundaries.

A healthy plant is not fed at pH 6.19 and suddenly blocked at pH 6.21. What matters is the development over time and the cultivation system as a whole.

Soil and Living Soil

For mineral soil, organic soil and Living Soil, a root-zone pH of approximately 6.0 to 7.0 is a sensible working range.

A well-functioning range is often between 6.2 and 6.8.

This does not mean that every irrigation water must be adjusted to exactly this value. Active soil has a certain buffering capacity. Its strength depends, among other factors, on organic matter, clay content, minerals, lime content and pot size.

Peat-based grow soil

For peat-based substrates, a range of approximately pH 5.5 to 6.5 in the substrate solution is common.

Many grow soils are already adjusted with lime. The initial value can change during the grow. Water quality, the fertilizer used and the form of nitrogen are particularly important influences on the further course.

Coco

For coco, a finished nutrient solution of approximately pH 5.7 to 6.2 is a sensible starting range.

Coco is managed more like a hydroponic substrate. The plant is therefore more directly dependent on the composition of the nutrient solution.

Coco also has exchange sites for positively charged nutrients. Calcium, magnesium, potassium and sodium can influence one another there. pH alone is therefore not sufficient for effective management.

Hydro and rockwool

In hydroponic systems and rockwool, a range of approximately pH 5.5 to 6.2 is common.

Many scientific cannabis trials use nutrient solutions around pH 5.6 to 5.8. However, hydroponic solutions often have little buffering capacity. pH can therefore change more quickly than in soil.

An important note about these values

Cannabis research is improving. However, there is still no scientifically established single value that is equally optimal for every genotype, substrate and growth phase.

In a study published in 2025 involving various hemp varieties, growth in a peat-perlite substrate was lower at pH 3.0 and 4.0 than from pH 5.0 onward. In another trial, root mass was reduced both at the lowest value studied, pH 3.1, and at the highest value, pH 7.1. The results show a functional corridor. They do not establish a universal ideal number for every cannabis grow.

How pH affects nutrient uptake

A nutrient does not only need to be present in the pot.

It must dissolve. It must be present in an absorbable form. It must reach the root. It must then pass through a functioning root membrane and be transported within the plant.

pH influences several of these steps:

• the solubility of certain nutrient compounds
• binding to substrate components
• precipitation with other elements
• the electrical charge of certain compounds
• the activity of roots and transport proteins
• microbial activity
• the breakdown and mineralization of organic matter

pH can therefore influence whether a nutrient remains freely available in solution or becomes more strongly bound.

However, it cannot create a nutrient that is not present.

Likewise, a perfect pH cannot repair damaged or chronically oxygen-deprived roots.

Nitrogen: nitrate and ammonium alter pH

Nitrogen is supplied to plants, among other forms, as nitrate and ammonium.

These two forms of nitrogen do not act the same way in the root zone.

Greater ammonium uptake can acidify the root zone. The microbial conversion of ammonium to nitrate also releases acid.

With stronger nitrate uptake, on the other hand, the root zone may develop more toward the basic range.

That is why the pH of two nutrient solutions can develop differently even when both contain the same total nitrogen.

The plant itself also influences this process. In current cannabis trials, researchers observed changes in the pH and EC of the nutrient solution during uptake. The researchers attribute part of this movement to the form of nitrogen and the uptake of charged ions.

A rising pH therefore does not automatically mean that the plant is healthy.

A falling pH is also not proof of overfertilization.

The direction provides a clue. It does not replace a diagnosis.

Phosphorus: present does not automatically mean available

Phosphorus is particularly relevant in cannabis cultivation. At the same time, it is one of the nutrients that can easily become bound or precipitate.

In strongly acidic mineral soils, phosphorus can bind more strongly to iron and aluminum. At high pH values, poorly soluble compounds with calcium can form.

Additional processes occur in organic substrates. Microorganisms, enzymes and organic acids can mobilize bound phosphorus. This biological mobilization is valuable. However, it cannot compensate for unfavorable basic conditions without limit.

More phosphorus therefore does not automatically solve an availability problem.

A 2025 cannabis study showed that greatly increased phosphorus concentrations and higher overall fertilization improved neither yield nor quality. More nutrients in the root zone did not mean greater performance.

Potassium: do not look only at the amount

Potassium remains soluble across a relatively broad pH range. Nevertheless, it can cause problems.

A high potassium supply can affect the uptake of other positively charged nutrients. Magnesium in particular, and calcium to some extent, must be considered as part of the overall supply.

In a cannabis trial on mineral nutrition, increasing phosphorus and potassium supply led to declining magnesium concentrations in plant tissue. This shows why a plant can develop deficiency symptoms despite having sufficient magnesium.

The problem is not necessarily the magnesium content.

It may lie in an unbalanced ratio.

Calcium and magnesium: not every CalMag deficiency is a true deficiency

Light leaf areas, rust spots or necrotic patches are quickly labeled a CalMag problem in cannabis cultivation.

That may be correct. But it does not have to be.

Calcium and magnesium uptake can be influenced by, among other things:

• a high potassium concentration
• high ammonium levels
• a high salt content
• unhealthy or damaged roots
• constantly wet substrate
• insufficient water movement within the plant
• unfavorable temperatures
• an unsuitable pH
• source water that is already rich in calcium

Additional CalMag is only useful if the overall supply is genuinely too low or unbalanced.

Anyone who doses more at every spot can intensify an existing imbalance.

Iron, manganese, zinc and copper

Many micronutrients become more soluble as pH decreases.

This applies especially to:

• iron
• manganese
• zinc
• copper

At too high a pH, these elements can become less available. Lightening of new growth is typical. Iron is only somewhat mobile within the plant. An availability problem therefore often first appears on new leaves.

At very low pH values, the opposite can occur. Micronutrients may then become so soluble that excessive concentrations and toxic effects are possible.

Molybdenum behaves differently

Molybdenum is an important exception.

While the availability of many micronutrients decreases as pH rises, molybdenum becomes more available in many soils as pH increases.

This is another reason why statements such as “the lower the pH, the better the nutrient uptake” are technically incorrect.

Case study from cannabis research: greater uptake can mean less growth

The previously mentioned 2025 cannabis study provides a particularly important indication.

At a low substrate pH of approximately 3.8, higher concentrations of several micronutrients were measured in plant tissue. At pH 6.5, the measured concentrations were lower.

Despite the higher micronutrient uptake, the plants grew less well in the strongly acidic range. Root growth was also restricted at extreme pH values.

This shows:

The greatest uptake is not automatically the healthiest uptake.

A cannabis plant does not need the maximum concentration of every individual element. It needs a balanced supply.

Why the familiar pH charts are only a guide

Almost every grower knows the colored charts with wide and narrow nutrient bars.

They give the impression that phosphorus is “open” at a certain value and “closed” shortly afterward.

That is not how the root zone works.

Actual availability also depends on:

• substrate type and mineralogy
• organic matter
• cation exchange capacity
• moisture
• oxygen supply
• temperature
• EC
• fertilizer form
• chelates
• root activity
• microbiology

A pH chart can show general tendencies. But it cannot account for your water, substrate or fertilizer formula.

The idea of a sharp boundary is particularly problematic. Availability usually changes gradually.

pH and EC must be considered together

pH does not describe the amount of dissolved salts.

EC is generally used for this in a grow.

This value also has limitations. EC shows the electrical conductivity of a solution. It does not show which nutrients are present or the ratios in which they occur.

Nevertheless, the combination provides important information:

Suitable pH and very low EC

The nutrient solution may simply be too weak.

Suitable pH and very high EC

The plant may have difficulty taking up water. Individual ions may accumulate. The risk of nutrient imbalances also increases.

Unsuitable pH and normal EC

Nutrients may be present. Their availability may nevertheless be restricted.

Unsuitable pH and high EC

Here, pH shifts, salt stress and antagonisms can occur at the same time.

Cannabis responds to salt stress not only through visible leaf damage. High salt concentrations also alter water uptake and the ratio of absorbed ions.

The biggest misconception: water pH and acid-neutralizing capacity are not the same

Tap water with pH 8 is often immediately classified as poor.

Water with pH 7.2, by contrast, appears unproblematic.

This assessment may be exactly backwards.

pH describes the current state of the water.

Acid-neutralizing capacity describes how much acid the water can neutralize. It is determined primarily by bicarbonate and carbonate.

Water with low acid-neutralizing capacity can be lowered easily despite a high initial pH. Other water may start at a lower pH and still require considerably more acid.

In professional plant production, alkalinity or acid-neutralizing capacity is therefore considered more important for the long-term development of substrate pH than the water’s pH alone.

Real-world water example: Rosenheim and Coswig

Two official German drinking water analyses clearly show the difference.

Rosenheim, Kreut elevated tank

The sample was taken on 7 July 2026.

• pH: 7.26
• Acid-neutralizing capacity to pH 4.3: 6.2 mmol/l
• Bicarbonate: 368.4 mg/l
• Calcium: 95 mg/l
• Magnesium: 22 mg/l
• Conductivity: 657 µS/cm

Coswig in Anhalt

The published values are from 16 March 2026.

• pH: 8.18
• Acid-neutralizing capacity to pH 4.3: 1.21 mmol/l
• Calcium: 43 mg/l
• Magnesium: 4.76 mg/l
• Conductivity: 311 µS/cm

The water from Coswig has the considerably higher pH.

Nevertheless, Rosenheim water has approximately five times the acid-neutralizing capacity. It therefore binds considerably more acid.

Coswig’s higher initial pH alone says little about how strongly the water will affect a substrate over the long term. Rosenheim water starts lower. Because of its high acid-neutralizing capacity, it can nevertheless push the pH of a pot substrate upward more strongly through repeated irrigation.

Acid-neutralizing capacity to pH 4.3 is not a direct dosing recipe for a grow solution at pH 6.2. However, it clearly shows the difference in buffering.

Rosenheim water also already contains 95 mg/l calcium and 22 mg/l magnesium. These amounts must be taken into account in a nutrient plan.

Anyone who adds CalMag indiscriminately here without accounting for the source water can create an unnecessarily high overall supply.

Why the substrate is affected by every irrigation

Bicarbonate does not act only in the watering can.

It enters the substrate with every irrigation. There it reacts with acid and consumes hydrogen ions. As a result, pH can slowly rise over a period of weeks.

This effect is often visible more quickly in small pots. The limited substrate volume provides less buffering than a large bed or a large Living Soil pot.

Frequent irrigation also increases the total input.

That is why a plant can look healthy for several weeks and later seemingly develop an iron or manganese deficiency suddenly.

The problem did not arise suddenly. It built up gradually.

MicroBio+ as a natural pH-down

MicroBio+ is naturally acidic.

It can therefore lower the pH of irrigation water while also introducing selected microorganisms into the system.

It contains:

• Lactobacillus plantarum
• Lactobacillus casei
• Rhodopseudomonas palustris
• Saccharomyces cerevisiae

The lactic acid bacteria and fermentative foundation it contains contribute to MicroBio+’s natural acidic effect.

MicroBio+ therefore combines two functions:

1. It can act as a natural pH-down.
2. It supplements the biological component in the root zone.

This combination is particularly useful in:

• organic soil
• Living Soil
• reused soil
• biologically managed coco
• biologically managed hydro systems

In many organic setups, this can reduce or completely eliminate the need for additional correction with nitric acid or phosphoric acid.

This has another advantage. Using pH-down does not automatically add additional nitrate or phosphate to the nutrient solution.

MicroBio+ does not replace the meter

Natural pH-down does not mean pH-down without control.

How strongly MicroBio+ lowers pH depends on the water’s acid-neutralizing capacity and buffering capacity.

With weakly buffered water, a small amount can already trigger a noticeable change.

With water like the Rosenheim example, the same amount may have a considerably smaller effect.

The current application recommendation is:

• Soil and coco: 2 to 4 ml per liter
• Bio-Hydro: 2 ml per 10 liters
• Reactivating old soil: 2 to 5 ml per liter

These are application amounts. They are not guaranteed pH target values.

MicroBio+ is added to the water first and mixed thoroughly. If additional fertilizers or additives are used, they are added according to the intended mixing schedule. The final pH is assessed only once the solution has been fully prepared.

This allows you to see what effect MicroBio+ has in your actual water and actual fertilizer mix.

With strongly buffered water, it may make more sense to mix part of the tap water with reverse osmosis water. This avoids continually adding more acid to counter a high bicarbonate load.

MicroBio+ should not be used at the same time as H₂O₂, fungicides or strongly disinfecting agents. These can impair or kill the microorganisms it contains. MicroBio+ is therefore not intended for hydro systems managed under permanently sterile conditions.

What microorganisms do in the root zone

Microorganisms can break down organic matter. They can produce compounds that dissolve or bind minerals. They compete with other microorganisms and respond to root exudates.

They therefore also influence local nutrient availability.

The rhizosphere is the small area directly around the root. Chemical and biological processes are particularly active there. Root exudates serve as food and signals for microorganisms. At the same time, they can alter the solubility of certain nutrients.

Active soil life can make a system more resilient. However, it cannot neutralize unlimited amounts of bicarbonate.

Microbiology therefore does not replace a water analysis.

It complements it.

Managing soil and Living Soil correctly

In soil and Living Soil, it is rarely useful to chase every minor deviation in irrigation water.

A well-constructed substrate can absorb fluctuations. The larger the substrate volume and the greater the biological and mineral buffering, the more slowly the system responds.

That does not mean pH becomes irrelevant.

You should pay particular attention when:

• the water has a high acid-neutralizing capacity
• only small pots are being used
• strongly alkaline water is used over a long period
• more and more deficiency symptoms appear at the same time
• new growth becomes increasingly pale
• the soil is being reused
• large amounts of basic additives are regularly introduced

In a stable Living Soil system, the trend matters more than a single measurement.

Water with pH 7.5 and low acid-neutralizing capacity can function without problems. Water with pH 7.2 and high acid-neutralizing capacity can shift the soil upward over a period of months.

MicroBio+ can be used here as a natural pH-down and microbial additive. Nevertheless, its effect should be measured.

Managing peat-based grow soil correctly

Peat naturally has a low pH. Manufacturers generally balance it with lime.

The amount of lime mixed in influences the initial value and long-term buffering. The particle size of the lime also plays a role. Finer particles react more quickly. Coarser particles act more slowly and for longer.

During the grow, water and fertilization alter this balance.

Water with high acid-neutralizing capacity can drive substrate pH upward. Fertilization heavily weighted toward ammonium can shift it downward. A predominantly nitrate-based supply can promote the opposite development.

When problems occur, do not measure only the input pH.

A standardized substrate measurement provides considerably more information.

Managing coco correctly

Coco has less chemical and biological buffering than robust soil.

At the same time, it has exchange sites for positively charged nutrients. Calcium, magnesium, potassium and sodium interact there.

For this reason, several values must always be considered together in coco:

• pH of the finished nutrient solution
• EC of the finished nutrient solution
• drain development
• irrigation volume
• irrigation frequency
• drying phase between irrigations
• calcium, magnesium and potassium in the overall mix

A pH of approximately 5.7 to 6.2 is a good working range.

Nevertheless, coco should not be corrected immediately in response to every deviation in the drain. The trend over several comparable measurements is what matters.

If coco dries out considerably, salts become concentrated in the remaining solution. As a result, EC and ion ratios in the root zone can differ significantly from those in freshly prepared nutrient solution.

Managing hydro and rockwool correctly

In hydro systems, pH responds more quickly.

The nutrient solution often has little buffering capacity. Root uptake, evaporation, top-up water, temperature and biological processes can change the value within a short period.

Regular measurement is useful here.

Nevertheless, you should not counteract every movement immediately.

Anyone who continually adjusts pH back and forth with pH-Up and pH-Down at every deviation introduces additional ions into the solution. At the same time, it becomes more difficult to identify the actual trend.

Small corrections are better than large jumps.

In recirculating systems, at least the following values should be monitored together:

• pH
• EC
• water temperature
• water consumption
• nutrient consumption
• root condition and color
• nutrient solution odor
• trend since the last refill

MicroBio+ is suitable in this area only for biologically managed Bio-Hydro systems. A permanently disinfected reservoir contradicts the purpose of living microorganisms.

What pH lockout really is

The term pH lockout sounds like a switch.

Correct pH means nutrients are available.

Incorrect pH means nutrients are unavailable.

This concept is too simplistic.

In grower terminology, pH lockout describes a situation in which unsuitable conditions in the root zone strongly restrict the availability or uptake of certain nutrients.

The change usually occurs gradually. In addition, not all nutrients respond in the same way.

At high pH, iron, manganese, zinc or copper can become less available. At the same time, molybdenum may become more available.

At low pH, certain micronutrients can become excessively soluble. At the same time, root growth may suffer.

pH lockout is therefore rarely a complete halt of overall nutrient uptake.

Not every alleged pH lockout is actually a pH problem

Many symptoms look similar.

A plant can show deficiency symptoms due to:

• overwatering
• oxygen deficiency
• high salt concentrations
• root damage
• low root-zone temperatures
• intense light with weak root function
• unbalanced nutrient ratios
• pests
• diseases
• unsuitable humidity
• insufficient transpiration
• actual nutrient deficiency
• unsuitable pH

With continuously wet substrate in particular, active nutrient uptake works less effectively. Roots need oxygen for their metabolism.

A plant with weakened roots can therefore look as though it has several deficiencies. In this case, additional fertilization often only increases the salt content.

Correctly interpreting signs on the leaves

Leaf symptoms provide clues. They rarely provide definitive proof.

Pale new growth

Possible causes include restricted availability of iron or manganese. Excessively high pH in the root zone may play a role.

Damaged roots, low temperatures or an unbalanced supply can also produce similar symptoms.

Lightening between the veins of older leaves

This may be consistent with a magnesium problem.

Possible causes include an actual deficiency, high potassium levels, high EC or impaired root function.

Burnt leaf tips

This is often interpreted as a pH problem.

More often, it indicates a high salt concentration or excessive fertilization.

Several deficiencies at the same time

If apparent calcium, magnesium, nitrogen and micronutrient problems occur simultaneously, the entire root zone should be checked first.

Several genuine individual deficiencies at the same time are less likely than a shared problem involving roots, irrigation, EC or pH.

Why a single drain value is not a diagnosis

Drain or runoff can provide useful information.

However, it does not automatically show the average pH of the entire pot.

The result depends, among other things, on:

• how moist the substrate was beforehand
• how much water was applied
• how quickly it was watered
• whether preferential water channels formed
• where salts accumulated
• which part of the substrate was actually flushed
• how much drain was collected

A study published in 2024 by the US Department of Agriculture showed that even a standardized Pour Through method more strongly reflected conditions in the lower pot area. The values therefore had to be considered in the context of sampling.

Normal runoff from a private grow is generally even less standardized.

A runoff value is an indication. It is not a verdict.

It only becomes genuinely useful when the same method is used every time. Timing, water volume and initial moisture must be comparable.

How to measure pH reliably

A pH meter is only as good as its condition.

A meter with an old, dry or contaminated electrode can display very precise numbers and still measure incorrectly.

Calibrate

For growing purposes, two-point calibration with pH 7 and pH 4 is sensible.

The calibration solutions should be fresh and clean. Used solution should not be poured back into the bottle.

Rinse the electrode

Between measurements, rinse the electrode with distilled or demineralized water.

The sensitive measuring tip should not be rubbed.

Store it correctly

A pH electrode should be stored in a suitable storage solution.

It should neither be allowed to dry out nor be kept permanently in reverse osmosis water, distilled water or demineralized water. This can damage the electrode and shorten its service life.

Measure the finished solution

First, all components are mixed in according to the intended mixing schedule.

Then the solution is mixed thoroughly. Only afterward is the final pH assessed.

For MicroBio+, the rule is: add MicroBio+ to the water first and mix. Then check its effect within the fully prepared irrigation solution.

Wait for a stable value

The electrode needs contact with the solution.

The displayed value should have stabilized. A value read immediately can be misleading.

Always measure in a similar way

Temperature, mixing time, container and measurement time should remain as comparable as possible.

This allows you to identify genuine trends rather than differences in measurement routine.

Testing soil and substrate correctly

Inserting a probe at an arbitrary point in the pot rarely provides a useful, comparable value.

Standardized methods are better.

These include:

• a defined substrate-water mixture
• a standardized Pour Through method
• a saturated substrate extract
• a laboratory analysis

The chosen method is not the only important factor.

It is important to use the same method every time. Different extraction methods can produce different pH and EC values.

For simple trend monitoring, a defined substrate-water mixture can be helpful. The amount of substrate, amount of water, mixing time and waiting time must remain constant.

For a fundamental diagnosis, a professional substrate analysis is more reliable.

What to do when you suspect a pH problem

1. Consider the entire pattern of damage first

Are young or old leaves affected?

Does the problem begin at the top, at the bottom or everywhere at once?

How quickly does it develop?

2. Check the roots and irrigation practices

Is the substrate constantly wet?

Does the root zone smell rotten?

Are visible roots light-colored and vigorous, or dark and soft?

3. Check the climate

Is the root zone very cold?

Is humidity so high that almost no transpiration takes place?

Is light intensity higher than the current root function can support?

4. Measure the finished nutrient solution

Check pH and EC after all additives have been included.

5. Check your source water

Do not look only at pH.

Also relevant are:

• acid-neutralizing capacity
• bicarbonate
• calcium
• magnesium
• sodium
• chloride
• sulfate
• electrical conductivity

6. Measure the root zone reproducibly

Use a standardized method or a laboratory analysis.

7. Change only one important variable

Anyone who flushes, adds more fertilizer, changes pH and applies additional additives at the same time cannot determine which measure worked.

8. Observe new growth

Already damaged leaves generally do not become fully healthy again.

What matters is how new leaves and shoots develop.

Correcting excessively high pH

First, it must be clarified what is actually too high.

High pH in tap water is different from high pH in the substrate.

Possible causes include:

• high acid-neutralizing capacity of the water
• high bicarbonate levels
• excessive liming
• basic additives
• a long-term diet heavily weighted toward nitrate
• a substrate unsuitable for the system
• incorrect measurement

Possible measures include:

• using MicroBio+ as a natural pH-down
• blending tap water with reverse osmosis water
• using a more suitable water source
• checking the fertilizer formula
• measuring the actual substrate development in soil
• continuing to acidify only in a controlled manner

Concentrated acids must never be applied undiluted to the roots.

Anyone using mineral acids must follow the concentration, application instructions and safety requirements. Blanket milliliter recommendations without a water analysis are not credible.

Correcting excessively low pH

A falling pH also has a cause.

Possible triggers include:

• too much pH-down
• very low acid-neutralizing capacity of the water
• fertilization heavily weighted toward ammonium
• biological decomposition processes
• an unsuitable or depleted substrate
• heavy salt accumulation
• faulty measurement

First, acid addition is reduced or stopped.

Then fertilization, water and substrate are checked. Rapid counter-correction with large amounts of pH-Up can destabilize the system further.

In soil, lime should only be added after an actual substrate or soil analysis.

Does pH need to be raised during flowering?

Not automatically.

The transition to flowering changes nutrient requirements and often the fertilizer formula as well. This can alter pH development.

However, this does not mean that cannabis suddenly needs a completely different pH from a certain flowering day onward.

The appropriate working range is determined primarily by the cultivation system.

A coco plant is not managed like a Living Soil plant during flowering. A Living Soil plant is not lowered to hydro values simply because it is now absorbing more phosphorus.

A slight movement within the appropriate range is normal.

Large intentional fluctuations are not necessary.

Outdoor cannabis and pH

Outdoor cultivation in natural ground follows different principles than cultivation in a small indoor pot.

Natural soil usually has a much larger volume. It contains mineral and organic buffers. As a result, the pH of an individual irrigation event often has less immediate significance.

For cannabis and hemp, mineral soils with approximately pH 6.0 to 7.0 are considered a good starting range. Depending on soil type and location, cannabis can also grow outside this range.

A soil analysis should be carried out before making any correction.

The sample should come from several locations and a comparable depth. A single handful of soil taken directly beside the stem is not representative.

Soil that is too acidic can be raised with suitable lime materials. Soil that is too alkaline can, depending on soil type, be influenced over the long term with sulfur-containing or organic measures.

Such changes take time.

Natural garden soil should not be acidified over a large area based on a single tap-water value.

If the outdoor plant is instead growing in a pot, largely the same rules apply as in an indoor grow. The limited substrate volume reacts considerably faster.

Frequently asked questions about pH in cannabis

What is the best pH for cannabis?

There is no single value for all systems.

As a practical guide:

• Soil and Living Soil: approximately pH 6.0 to 7.0 in the root zone
• peat-based grow soil: approximately pH 5.5 to 6.5 in the substrate solution
• coco: approximately pH 5.7 to 6.2 in the finished nutrient solution
• hydro and rockwool: approximately pH 5.5 to 6.2 in the nutrient solution

Is tap water with pH 8 unsuitable for cannabis?

Not automatically.

Water with pH 8 and low acid-neutralizing capacity can be easier to manage than water with pH 7.2 and high bicarbonate levels.

The water analysis is more important than the individual pH value.

Do I always need to adjust Living Soil water to pH 6.5?

No.

Active Living Soil can buffer fluctuations. Acid-neutralizing capacity, substrate volume and long-term development are what matter.

With water containing high levels of bicarbonate, correction may nevertheless be useful.

Is MicroBio+ a pH-down?

Yes.

MicroBio+ is naturally acidic and can lower the pH of irrigation water. At the same time, selected microorganisms are introduced.

The actual pH reduction depends on the water’s buffering capacity. This is why pH should always be measured after adding it.

Can MicroBio+ replace mineral pH-down?

In many organic and biologically managed setups, MicroBio+ can reduce or eliminate the need for a separate mineral acid.

With very high acid-neutralizing capacity, additional water treatment or controlled correction may still be necessary.

Does runoff show the pH of the soil?

Not exactly.

Runoff is strongly influenced by the lower part of the pot, irrigation and salt accumulation.

It is primarily useful as a standardized measurement over time.

Should I flush immediately in the event of pH lockout?

Not without a diagnosis.

Flushing can be useful in salt-loaded coco or a mineral-based substrate. In organic soil or Living Soil, unnecessary flushing can leach out nutrients and disturb the biological system.

First, the cause, substrate and EC must be clarified.

Will a leaf recover after a pH correction?

Severely damaged tissue usually does not recover fully.

Assess the result based on new leaves, new shoots and subsequent development.

Conclusion: the number alone does not decide

The plant introduced at the beginning may not have had an empty pot.

It may have had enough nitrogen, phosphorus, potassium, calcium and magnesium.

Nevertheless, it could not use this supply properly.

Perhaps the root zone was constantly too wet. Perhaps the EC was too high. Perhaps bicarbonate-rich water had shifted the substrate pH over a period of weeks. Perhaps a high potassium supply blocked magnesium uptake.

The visible deficiency was merely the end of a longer development.

That is precisely why it is not enough to measure the pH of the watering can and then open another bottle.

A stable grow arises from the interaction of:

• suitable water quality
• appropriate pH range
• balanced nutrient supply
• healthy root zone
• correct irrigation
• adequate oxygen
• functioning microbiology
• clean and repeatable measurement

MicroBio+ can be used as a natural pH-down and as a microbial component. However, it replaces neither water analysis nor the meter nor a suitable nutrient plan.

pH is not an end in itself.

It is a tool that helps you understand what happens between water, substrate, microorganisms and roots.

You do not control the plant.

You control the system.

Technical foundation

• In 2025, Veazie et al. studied the influence of different substrate pH values and micronutrient concentrations on Cannabis sativa.
• In 2024, Kpai et al. studied the mineral nutrition of cannabis during the vegetative phase and described, among other things, pH changes and interactions between potassium, phosphorus and magnesium.
• Bevan et al. studied the NPK supply of cannabis during flowering in a soilless system.
• In 2024, Altland and Owen showed that Pour Through samples more strongly reflect the lower part of the pot.
• The University of Georgia describes the relationships between pH, alkalinity, water quality, fertilizer form and substrate development.