How To Keep pH Stable In Soil (Secrets to Stop pH Changes)


Does your soil pH tend to “drift”, becoming more acidic or basic over time?  If so, then you are familiar with adding amendments, such as lime or sulfur, to rebalance your soil pH.  However, it is both time-consuming and expensive to do this for large areas every year.  I was curious, so I did some research to find out if there is a way to maintain the stability of soil pH.

So, how do you keep pH stable in soil?  One way to keep pH stable in soil is to add compost, especially if your soil is naturally sandy.  Improving drainage will also help to keep your soil pH stable.  In addition, you should also avoid amendments that alter soil pH, such as nitrogen fertilizers.

Let’s start off by looking into why these methods will help to stabilize soil pH.  Then, we’ll get into common ways that gardeners unknowingly raise or lower soil pH so that you can avoid making those mistakes.

How To Keep pH Stable In Soil

There are a few main methods to keeping the pH stable in your garden soil: adding compost, improving drainage, and avoiding amendments that alter pH.  You should be doing the first two in most gardens anyway, so if you aren’t, now is as good a time as any to get started.

Add Compost To Keep Soil pH Stable

When you add finished (completely decomposed) compost to your garden, it will add organic material to your soil.  This organic material helps to stabilize pH by improving soil drainage (more on this later).

compost bin
Finished compost is a great way to help maintain soil pH stability.

Compost also replaces nutrients that your crops remove from the soil as they grow.  This prevents any imbalance in nutrients such as calcium, magnesium, or potassium, which in turn prevents soil from becoming too acidic or too basic.

Improve Drainage To Keep Soil pH Stable

Improving drainage in your garden will also help to maintain a more stable soil pH.  Striking the right balance in soil moisture levels is the key to a healthy garden.

You want your soil to absorb some moisture, rather than repelling water and washing away topsoil and nutrients when it rains.  However, you also want the soil to dry out over time, so that a plant’s roots do not develop root rot from sitting in water.

One way to improve soil drainage is to add compost to your garden.  In addition to adding nutrients, compost adds organic material, which helps to make clay soil drain faster.

Compost also makes sandy soil drain more slowly, which prevents nutrients from leaching away after rainfall or watering.  When these nutrients do leach away, they can cause pH to drift (usually down, meaning more acidic soil).

For more information, check out my article on how to make your own compost.

You should also consider elevating your soil, either with mounds or raised beds.  This will allow water to flow away from your plants, and will prevent them from sitting in too much water.

If your plants do get flooded during a brief period of heavy rain in the summer, nutrients can be washed away, which can lead to pH swings.

PVC Pipe
You can lay pipe to help improve drainage if needed.
PVC Pipe Courtesy of user UsKhalid at Wikimedia Commons: https://commons.wikimedia.org/wiki/File:The_PVC_pipe.jpg

If you have areas in your garden that flood regularly, consider digging trenches or installing pipes to improve drainage.  Otherwise, you will see mulch, topsoil and nutrients washed away every time it rains.

You may see swings in soil pH, which in turn may require lime or sulfur amendments every year.

Avoid Amendments That Alter Soil pH

If your soil lacks calcium, you might have received advice to amend your soil with lime (calcium carbonate) or dolomitic lime (calcium magnesium carbonate).  However, lime and dolomitic lime also have the effect of raising soil pH, which makes your soil more basic.

In order to avoid this, use another amendment to supplement calcium.  For instance, gypsum (calcium sulfate) supplements both calcium and sulfur, but does not affect pH in the way that lime does.

You can also use bone meal, which is high in calcium, to fertilize individual plants before you put them in the ground.

If your soil needs magnesium, Epsom salt (magnesium sulfate) is a better choice than dolomitic lime, since Epsom salt has a pH that is approximately neutral.

Also remember that some amendments, such as nitrogen or sulfur fertilizers, can lower pH, making your soil more acidic. For tips on how to avoid high nitrogen levels in soil, check out my article on low-nitrogen fertilizers.

Most plants prefer a pH that is slightly acidic to almost neutral (6.0 to 6.8). Of course, there are exceptions to this rule.

For instance, there are some plants that require more acidic soil, such as blueberries, azaleas, and potatoes.  In these cases, you may need to use some acidifying soil amendments to achieve the proper pH.

The best way to make sure you have the proper soil pH is to do a soil test.  You can use a do-it-yourself soil test kit, which you can buy online or at a garden center.

You can also send a soil sample for testing in the lab at your local agricultural extension.  These tests will give you more detailed information and more accurate results than a do-it-yourself soil test.

In addition, if you send information on what you are growing in your garden, these labs will offer recommendations about how to treat your soil.

For more information, check out my article on how to do a soil test and my article on what a soil test tells you.

If your soil pH is not at the correct level, you will want to adjust it before attempting to keep it stable.  A soil test can tell you this.

If your soil pH is too low (acidic), check out my article on how to raise soil pH.

If your soil pH is too high (basic), check out my article on how to lower soil pH.

What Causes Soil pH To Go Down (Become More Acidic)?

There are several reasons that your soil may become more acidic over time.  One big reason, mentioned earlier, is the use of nitrogen or sulfur fertilizers, such as ammonium nitrate.

Adding too much sulfur to your soil will also lower soil pH.  It is true that sulfur is indicated as an amendment if your soil pH is too high.

sulfur
Sulfur will lower soil pH, but make sure to give it time to work before adding more!

However, it takes time for sulfur to have its full effect.  For example, let’s say that you add some sulfur to lower your soil pH and then measure again a week later.  The pH will still decrease by quite a bit in the coming weeks, so if you add more sulfur, you will “overshoot” and end up with soil that is too acidic.

Remember that nutrients leached from the soil due to rain can also cause acidic soil.  When nutrients such as calcium, magnesium, and potassium are leached from soil due to flooding or heavy rain and watering, you can be left with acidic soil.

Rain also becomes acidic when water reacts with atmospheric carbon dioxide to form carbonic acid.  This effect will be even more pronounced with acid rain (caused by air pollution).

The decay of organic material can also cause pH to drop, so make sure that any compost or manure you add to your garden is completely decomposed. 

Finally, remember that plants can cause soil pH to drop.  As plants grow, they absorb nutrients from the soil.  This change in nutrient levels can acidify the soil over time, especially if you don’t replace those nutrients with compost and fertilizer.

What Causes Soil pH To Go Up? (Become More Basic)?

If you have excessive amounts of alkaline elements, such as calcium or magnesium, you can end up with basic soil (high pH).  As mentioned earlier, this is more likely if you amended your soil with lime, dolomitic lime, or Epsom salt to supplement calcium or magnesium.

Why Is pH Important In Gardening?

Soil pH is important in gardening because every plant has a specific range of pH values where it can thrive.  In addition, the availability of nutrients in the soil is dictated in part by soil pH.

If soil pH levels are too low or too high, plants will not be able to absorb nutrients from the soil.  This is true even if there is plenty of the nutrient in the soil!

This is why it is so important to understand soil pH and to do soil testing.  Otherwise, you won’t know if a plant’s nutrient deficiency is caused by deficient nutrients in the soil, excessive nutrients in the soil, or soil that is too acidic or basic.  This can lead you to supplement nutrients that are not necessary, which can make a problem worse!

For more information, check out this chart from Research Gate, which shows the effect of soil pH on nutrient availability.

Conclusion

Now that you have an idea of how to keep your soil pH stable, you can get to work on making the necessary changes.  Remember to avoid the common mistakes that will cause your soil pH to swing up or down.

I hope you found this article helpful – if so, please share it with someone else who can use the information.  If you have any questions or advice of your own about keeping soil pH stable, please leave a comment below.

jonathon.david.madore

Hi, I'm Jonathon. I’m the gardening guy (not guru!) who is encouraging everyone to spend more time in the garden. I try to help solve common gardening problems so that you can get the best harvest every year!

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