pH in hydroponics: what level to aim for and do you really need to measure it?

pH in hydroponics: what value to aim for and do you really need to measure it?

Your basil is getting light. The reservoir contains water and hydroponic nutrients. Yet, the leaves are starting to pale.

Your first instinct would be to add nutrients.

That is not necessarily the right answer.

They may already be present in the water, but the plant may have more difficulty absorbing them if the pH of the solution is not right.

This is where pH becomes interesting.

Good news: to grow a few herbs or lettuces at home, you do not need to spend your day with a test tube in hand.

You mainly need to understand what you are measuring, know a reasonable range, and know when checking it really becomes useful.

What exactly is pH?

pH indicates whether a solution is acidic, neutral, or alkaline.

The scale goes from 0 to 14:

• below 7, the solution is acidic;

• around 7, it is neutral;

• above 7, it is alkaline.

But this scale has one important feature: it is logarithmic.

A difference of one unit therefore represents a much greater difference than it appears.

In your indoor garden, what we are mainly interested in is the pH of the nutrient solution, that is, the water in which the hydroponic nutrients are dissolved.

Why is pH important in hydroponics?

Because it influences the availability of nutrients to the roots.

Penn State Extension reminds us that pH plays an important role in the availability of minerals. A nutrient may be present in the solution without being as easily available to the plant when the pH is outside the suitable range.

This is an important difference.

A plant showing signs resembling a deficiency therefore does not necessarily need more nutrients.

The problem may be their availability.

Adding even more fertilizer without checking the rest can then unnecessarily increase the concentration of the solution without solving the original problem.

This is also what explains why pH is particularly monitored in hydroponics: unlike growing in soil, you have much less buffering around the roots.

What is the ideal pH in hydroponics?

There is no single perfect number that applies to all plants.

Horticultural references, however, use a slightly acidic range for most hydroponic crops.

Oklahoma State University generally recommends a pH of 5.0 to 6.0 for hydroponic growing, while its guide on nutrient solutions indicates that a pH around 5.5 helps maintain favorable conditions in the root environment.

Other references give slightly wider ranges.

Penn State Extension, for example, places the general optimal range for hydroponic vegetables between 5.0 and 7.0.

Why are these numbers not exactly the same?

Because the right value also depends on the plant.

Oklahoma State University indicates, in particular:

• basil: 5.5 to 6.0 ;

• lettuce: 6.0 to 7.0 ;

• parsley: 6.0 to 6.5 ;

• tomato: 6.0 to 6.5 ;

• bell pepper: 5.5 to 6.0.

The goal, therefore, is not to stubbornly aim for 5.8 for all your crops.

For a small hydroponic garden with several plants, look instead for a slightly acidic range compatible with the crops present.

Should you measure the pH from the very first crop?

Not necessarily.

If you start with a few lettuces or some basil, use proper water, follow the dosage of your hydroponic nutrients, and observe your plants.

You can very well learn the first steps without measuring the pH morning and evening.

Measuring becomes particularly interesting when:

• the plants regularly show unexplained symptoms;

• growth remains poor despite suitable lighting and nutrition;

• your water is very hard;

• you want to grow more demanding plants;

• you want to better control your nutrient solution.

In other words: pH is a tool for understanding, not a mandatory ritual every time you look at your garden.

How to measure the pH of your hydroponic garden?

Two solutions are common.

Test strips or colorimetric tests

They are simple and inexpensive.

You take a little solution, perform the test, then compare the resulting color with the provided scale.

For a first check, this may be enough.

The downside is precision: interpreting a shade between two colors is not always easy.

Electronic pH meter

It directly displays a numerical value.

It is more convenient if you want to perform measurements regularly.

But a pH meter is not magic.

It must be maintained and calibrated according to the manufacturer's recommendations. A poorly maintained probe can give a seemingly precise value... but a false one.

For an occasional user, a simple test can therefore be more relevant than an electronic device bought and then left in a drawer for several months.

Should you measure the pH of the tap water or that of the reservoir?

The pH that directly concerns your plants is that of the final nutrient solution.

Why?

Because adding nutrients can change the characteristics of the water.

Measuring only the water coming out of the tap and then considering this value as that of your garden is therefore not enough.

There is a second subtlety: the pH of the water alone does not tell the whole story.

Penn State highlights in particular the importance of alkalinity, which simply corresponds to the water's ability to neutralize acids.

Two waters with initially similar pH can therefore behave differently once used in a growing system.

Highly alkaline water will therefore be more likely to cause the pH of the solution to rise over time.

You do not need to have your water systematically analyzed to start.

But if your pH constantly rises despite your corrections, the quality of the starting water deserves to be examined.

Why does the pH change in the reservoir?

Because your garden is alive.

The roots take in water and minerals. The composition of the solution changes. You sometimes add water. The plants grow. Conditions change.

The pH can therefore gradually drift.

A small variation is not necessarily worrying.

The bad instinct is to try to maintain a perfectly fixed value to the tenth, correcting the solution several times a day.

For a home garden, first look for a consistent and relatively stable range.

If the pH regularly and significantly falls outside this range, look for the cause rather than multiplying corrections.

How to lower or raise the pH?

There are solutions specifically designed to adjust the pH of hydroponic crops, often sold under designations such as pH- and pH+.

The principle is simple.

If your solution is too alkaline, a suitable corrector allows you to lower its pH.

If it is too acidic, another allows you to raise it.

But proceed gradually.

A small reservoir represents a small volume of water: a quantity that seems tiny can therefore have a major effect.

Follow the manufacturer's dosage for the corrector, mix the solution properly, then measure again before adding more.

And above all, do not improvise with just any household product simply because it is acidic or alkaline.

You are potentially growing plants intended for consumption.

Can you use vinegar or baking soda?

You will easily find this tip on the Internet.

The problem is not just succeeding in moving the number displayed by the test.

The goal is to maintain a nutrient solution suitable for the roots over time.

Oklahoma State University mentions certain acids, including phosphoric acid or citric acid, to treat problems related to water alkalinity in horticultural contexts.

This does not mean that you should randomly pour cooking vinegar into your garden.

For a home system, preferably use a corrector intended for this purpose and follow its instructions.

You will avoid a good part of the useless experiments.

Can a bad pH make the leaves turn yellow?

Yes, indirectly.

An unsuitable pH can reduce the availability of certain elements.

At a high pH, Penn State indicates in particular that the availability of several micronutrients can decrease. Oklahoma State also highlights that a pH above 7 can reduce the availability of elements such as iron, manganese, copper, zinc, or boron.

But a yellow leaf does not constitute a pH test.

It can also signal:

a nutrient problem;

roots in poor condition;

a lack of light;

a naturally aging leaf;

or other unsuitable growing conditions.

So never correct the pH solely because a leaf has changed color. Measure first.

What if my plants grow very well with an imperfect pH?

Then do not look for a problem that does not exist.

The recommended values are agronomic ranges intended to promote good absorption conditions.

They are not magic boundaries.

A lettuce does not instantly stop growing because your solution momentarily goes from 6.0 to 6.2.

This is precisely the point of thinking in terms of a range rather than a perfect number.

Observe your plants.

Measure when it provides useful information.

And intervene when you identify a real drift.

It is much simpler than turning every reservoir refill into a laboratory session.

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pH and nutrients: the two go together

pH does not feed your plant.

Hydroponic nutrients, on the other hand, provide the minerals it needs.

pH helps create conditions in which these elements remain available to the roots.

This is why the two topics are linked.

When you encounter a problem, therefore, avoid thinking with only one variable.

Before adding more nutrients, look at the water, the roots, the light, and, when justified, the pH.

This approach is often more useful than multiplying products.

→ Discover Belverdia hydroponic gardens

What pH to choose when starting in hydroponics?

Remember three things above all.

Most hydroponic crops appreciate a slightly acidic solution, even if the exact range varies depending on the plant.

pH influences the availability of nutrients: a plant can therefore encounter a problem even if the necessary elements are present in the reservoir.

Finally, you do not need to adjust your water to the tenth every day.

Start by following the dosage of your nutrients, observe your plants, and measure when you have a reason to do so.

pH should help you understand your garden.

Not prevent you from enjoying it.