Does Lemon Juice Lower pH? (How It Can Hurt Plants)


It is always a bonus if you ca grow plants without using harsh artificial chemicals. Lemon juice is often suggested as a natural way to lower pH,

So, can you use lemon juice to lower pH?  Adding lemon juice (which has a pH of about 2.3) to water will lower pH.  However, doing so may harm your plants in a hydroponic or traditional gardening system. Lemon juice acts as an antimicrobial agent, which means that it kills bacteria and fungi.  This includes beneficial bacteria in water or soil that help your plants to grow!

Of course, there are other ways besides lemon juice to adjust pH in water or soil.

In this article, we’ll take a look at the science behind why you should not use lemon juice to lower pH.  Then, we’ll get into other ways you can lower pH and what to look out for.

Let’s begin.

Does Lemon Juice Lower pH?

Lemon juice will lower pH when added to water. Lemon juice has a pH of about 2.3 (very acidic), while most water is in the range of 6.5 to 8.5 for pH (slightly acidic to somewhat basic).

lemon juice
Lemon juice lowers the pH of water, but it can also kill beneficial bacteria.

If you add enough lemon juice to water, the acidity (low pH) will kill bacteria. According to North Dakota State University, lemon juice is often used in home canning to lower pH.

This lower pH prevents the growth of botulism (caused by the bacteria Clostridium botulinum) in canned food products. However, the acidity of lemons is not the only thing that can kill bacteria.

Even if you add a small amount of lemon juice and keep the pH at a reasonable level, lemons can still kill bacteria. The reason is that lemons contain flavonoids, which are a specific type of antioxidant.

lemons on tree
Lemons contain flavonoids that act as antimicrobial agents.

Flavonoids give lemons their antimicrobial properties.  When you add lemon juice to your garden or hydroponic system, you run the risk of the flavonoids killing the beneficial bacteria that live there.

(For more information about the study on antimicrobial activities of citrus juice concentrates, including lemon, check out this article on the NCBI site.)

Furthermore, some of the bacteria living in your system are nitrogen-fixing.  This means that they take nitrogen gas from the air and convert it into ammonia and nitrates.

These nitrogen compounds are necessary for plants to grow, since plants cannot take nitrogen directly from the air.

Nitrogen is one of the most important nutrients for plant growth.  It is found in the compound chlorophyll, which makes plants green.

lettuce
Hydroponic lettuce – looks like this plant got enough nitrogen!

Chlorophyll also helps plants to create energy (sugar) from water, carbon dioxide, and light through photosynthesis.

Now we’ve uncovered why you should not use lemon juice to lower pH in a garden or hydroponic system.  For the same reason, you should not use the juice of citrus fruits, such as limes, oranges, or tangerines, to lower pH.

These substances also contain flavonoids that have antimicrobial properties.  Again, this would be bad news for the nitrogen-fixing bacteria that help to feed your plants.

So, if you shouldn’t use citrus juices to lower pH, what should you use?  It’s time to talk about the right way to lower pH in a garden or hydroponic system.

How To Lower pH In A Garden Or Hydroponic System

To lower pH in garden soil, you can use elemental sulfur. It works slowly, but this also means that it is difficult to burn your plants with a fast pH change.

sulfur powder
Elemental sulfur will slowly lower soil pH, making it more acidic.

Common nitrogen fertilizers, such as ammonium nitrate and ammonium sulfate, will also lower pH. However, they can work fast, and it is easier to burn your plants with a rapid change in pH.

You can learn more about how to lower soil pH in my article here.

To lower the pH in a hydroponic system, you should use something called pH DOWN.  As the name suggests, you simply add pH DOWN to a hydroponic solution to lower the pH.

As an example, the General Hydroponics pH DOWN solution is formulated using food grade phosphoric acid, along with citric acid and mono ammonium phosphate.

Food grade simply means that pH DOWN is safe to use for growing hydroponic plants intended for human consumption. You can purchase pH down at hydroponic supply stores, either online or in-person.

You can save money by purchasing in bulk quantities (for example, 1 gallon instead of 1 quart).  However, if you are just starting hydroponics as a hobby, it might be better to start with a small bottle until you get your bearings.

Cautions When Adjusting pH

When adjusting pH, always follow the instructions on the label. Adding too much sulfur can lead to soil that is too acidic later on.

Remember that pH DOWN contains a strong acid, so you need to be careful when handling it.  Don’t get it on your skin, in your eyes, or in your mouth.

Also, be careful not to splash it on the leaves of your plants, since it will burn them.

In addition, the pH DOWN solution is buffered, meaning that it resists changes in pH.  This helps to keep the pH of your system stable.

However, from the planet natural website, you should be careful:

“when pH unstable media – such as rock wool or gravel products – are used, or when high plant growth rates destabilize the mix”.

https://www.planetnatural.com/product/general-hydroponics-ph-down/

(I will go into more detail about how high plant-growth rates can change pH later in the article).

When you add pH DOWN to your nutrient solution, make sure to do it gradually.  A large drop in pH in a short time can stress and damage your plants.

Start off by adding a small amount to your water. Add less than you think you need, since pH DOWN is very acidic.

I am talking about a fraction of a teaspoon to start with.  Mix thoroughly, wait a bit (perhaps 30 minutes), and see how much the pH changes before you add more.

soil test kit
Use a soil test to track the pH of your soil.

If you happen to overshoot with pH DOWN and the pH becomes too low, you can always add pH UP to counter the effect.  However, this is a waste of both products, and it takes time to seesaw back and forth.

Also, your plants might not like the swings in pH, so try to get it right the first time!

Finally, remember that the ideal pH range will vary by plant, but a good general range is 5.5 to 6.5 (slightly acidic).

What Else Can Affect pH Balance?

There are some other factors that can affect the pH of a garden or hydroponic system, including:

  • Adding Nutrients
  • Plants Using Nutrients
  • Temperature & Carbon Dioxide (in hydroponic systems)

Adding Nutrients

The first factor that affects pH is the concentration of nutrients in your soil or hydroponic solution.  The nutrients are not always neutral, so when you add them to your system, they will change the pH.

For example, when you add calcium to soil in the form of lime (calcium carbonate), this will also raise the pH.

calcium carbonate
Lime (calcium carbonate) adds calcium to soil and raises pH.

To counter this, make sure to add nutrients before you try to balance pH, or you will end up with a solution that is too acidic or too basic.

Plants Using Nutrients

The second factor affecting pH is the uptake of water and nutrients by your plants.  When plants use dissolved nutrients from soil or water, the pH move up or down (this is known as pH drift.)

As your plants grow, they will use both water and nutrients.   Ideally, the plants will use water and nutrients in such a way that the pH and concentration of nutrients stays roughly constant.

However, you will often see plants using one resource (water or nutrients) at a faster rate than the other.

hydroponics
These hydroponic plants are growing happily.

When plants use water faster than they use nutrients in a hydroponic system, the solution becomes more concentrated with nutrients. This leads to a higher TDS (total dissolved solids) or EC (electrical conductivity).

When plants use nutrients faster than they use water, the solution becomes less concentrated. This leads to a lower TDS or EC.  In this case, you will need to add nutrients to the system.

In both cases, you will need to add water to the system to replenish what the plants have used for growth.  Distilled water or reverse osmosis water is the best choice, since it has few dissolved solids in it.

Also, distilled water does not contain chlorine, which is often found in municipal tap water.  As you might guess, cities and towns use chlorine to kill microbes in the water supply.

While this is good for public health, it is not good for the bacteria in your soil or hydroponic system!

Of course, you can always just leave your tap water sitting in a bucket for a day or so. This will give the chlorine time to evaporate away.

However, tap water can still contain other solids, including iron, copper, or various trace minerals.  Make sure to test the PPM (parts per million) of the water to get an idea of what it contains before you use it.

Temperature & Carbon Dioxide

The third factor affecting pH in a hydroponic system is temperature and carbon dioxide in the air.  Carbon dioxide gas will dissolve in water to form carbonic acid.

thermometer
Water temperature affects dissolved carbon dioxide, carbonic acid, and pH.

More carbonic acid in the water will lower the pH of your system.  Remember that as water gets colder, more carbon dioxide will dissolve in the water, leading to more carbonic acid and a lower pH.

On the other hand, keeping your water warm will result in less dissolved carbon dioxide, which means less carbonic acid, and a higher pH.

Before adding pH DOWN, make sure to check the temperature of your system, and adjust downward if appropriate.  Just make sure that the new temperature is within the range that your plants can tolerate.

If you find that the temperature of your water is consistently too high, make sure that your grow lights are not giving off too much heat.  Another option is to use a water chiller for your system.

Other Questions About pH

There are a couple of other questions about pH that we should address.  We already talked about lowering pH, so let’s briefly touch on raising pH.

Can I Use Baking Soda To Raise pH?

Baking soda will raise pH when dissolved in water.  However, this will also increase the sodium content of your water.

This is not a recipe for success when growing plants!  Sodium can restrict the uptake of calcium, which a necessary nutrient for plant growth.

baking soda
Baking Soda, or sodium bicarbonate

The right way to raise pH is to use pH UP, which contains potassium hydroxide and potassium carbonate.  The pH of the General Hydroponics brand is 11.4 to 11.9.  You can check the price of pH UP on the planet natural website.

As with pH DOWN, you should avoid getting pH UP on your skin, in your eyes, or in your mouth.  A strong base can burn you just as badly as a strong acid!

In addition, be careful not to splash it on the leaves of your plants, or you will burn them.

Finally, be sure to add only a small amount of pH UP at a time, to gradually raise the pH of your solution to the desired level.

What Does pH Mean?

The term pH means potential of hydrogen, or the concentration of H+ (positively charged hydrogen ions) in a solution.  A higher concentration of hydrogen ions means a lower pH, and a more acidic solution.

A pH has a range from 0 to 14.  A pH of 7 is considered chemically neutral.  Anything below 7 is an acid, and anything above 7 is a base.

One key thing to remember about pH is that it is based on an exponential (or logarithmic) scale.  So, a solution with a pH of 6 has ten times the hydrogen ion concentration of a solution with a pH of 7.

Similarly, a solution with a pH of 5 has one hundred times the hydrogen ion concentration of a solution with a pH of 7.

You can imagine how quickly this grows: a solution with a pH of 1 has one million times the hydrogen ion concentration of a solution with a pH of 7.

Conclusion

Now you know that lemon and other citrus juices are not suitable for lowering pH, due to the potential to harm bacteria.  Similarly, baking soda is not suitable for raising pH, due to the sodium content.

The key takeaway is to start slowly, gradually changing your pH.  Otherwise, you run the risk of overshooting the target pH range and damaging your plants.

I hope this article was helpful in explaining a bit about pH – if so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

Recent Posts