How to Lower Soil pH

Need to lower soil pH in your garden? You have several options available to you. Which option is best depends upon several factors. But moving your garden soil pH lower may be as simple as adding fertilizer or mulch.

Of course, all methods of changing soil pH involve adding something to the soil. It’s just a question of the type of soil amendment you’ll be using, and in what quantity.


Before Starting…

Before starting the process of lowering soil pH, it’s important to test your soil.

It’s not enough just to know that you need to lower it. You should also know how much you need to lower it, because that will help you determine the type and quantity of soil amendment you’ll be using.

Also, consider whether lowering soil pH throughout your garden is really necessary.

If you just want to grow a few acid loving plants – blueberries or azaleas, for example – you might want to consider growing them in containers.

It’s much easier to adjust and maintain the pH in containers than it is to do it for your entire garden, or even for just a section of your garden.

Because lowering pH is not a ‘once and done’ proposition.

Most alkaline soils will gradually revert back to their natural pH levels, so maintaining an artificially lowered pH will require ongoing monitoring and maintenance.

So minimizing the area in which you’re trying to maintain a lower soil pH will make life easier.

And you should be aware that if your soil pH is really high – above 7.5 – you probably won’t be able to reduce the pH effectively enough to grow plants that need strongly acidic soil.


Using Fertilizer or Mulch to Lower Soil pH

If you just need to lower soil pH by a small amount, using certain types of fertilizers or organic amendments such as mulches can be both easy and effective.

  • Ammonium Sulfate or Urea
    These are both commonly used as nitrogen fertilizers. If you need to add nitrogen to your soil anyway, this can be an effective method of tweaking your garden soil pH.

    But be sure to only add as much fertilizer as necessary to meet your plants requirements for nitrogen.

    Adding extra fertilizer just for the pH lowering effect will cause more problems than it will solve.

    Using fertilizer to lower pH will have only a very slight impact on soil pH. But depending upon your situation, it may be all you need.

    NOTE: Be aware that fertilizers containing nitrogen in a nitrate form will have the effect of slightly increasing the pH of your soil.

  • Sphagnum Peat Moss
  • The pH of Sphagnum peat is quite low, generally ranging from about 3.0 to 4.5. Working peat into the soil before you plant can also add needed organic matter to the soil in addition to lowering pH. Just add an inch or two of peat to the soil surface, and mix it thoroughly with the topsoil down to about a foot beneath the surface.

  • Mulch
  • Pine bark and pine needles are both acidic, and applying them as a mulch will help to slightly lower the pH of your soil.

    A mulch made from shredded hardwood, though, will tend to raise the pH.


Using Sulfur to Lower Soil pH

You can make larger adjustments to your garden soil pH by using some form of sulfur.

Sulfur lowers soil pH as it is broken down by bacteria in the soil and converted to sulfuric acid. Sulfur is most commonly added in the forms of aluminum sulfate, iron sulfate and elemental sulfate.

Aluminum sulfate and iron sulfate both work to reduce the pH rapidly, but must be added in larger quantities than elemental sulfur. To lower your pH by about 1.0, for example, would require about 1.5 pounds of sulfur per 100 square feet, and 12.5 pounds of iron sulfate per 100 square feet.

But the iron sulfate would lower the pH in just a few weeks, while the elemental sulfur would take months to become fully effective.

It’s generally recommended that you not add aluminum sulfate to your soil in large quantities because it may result in aluminum toxicity to your plants.


Plan Ahead

Changing soil pH can be a long term project.

Depending upon how much you need to lower soil pH, it might take as long as a year to get the job done. So it’s best to plan ahead.

And though you can easily test your garden soil pH yourself, it’s best to have your soil tested initially by a soil testing lab. They’ll give you specific recommendations about methods and materials for changing your soil pH.





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