Soil pH Adjustment –
Raising and Lowering Soil pH

Soil pH adjustment is necessary when the pH level is greater than 0.5 more or less than your plants’ preferred range. If you plant crops in soil that is too acidic or alkaline, they will either not grow as well or not grow at all.

Adjusting soil pH with the proper amount of material depends on a number of factors including current pH level, your soil’s texture (sandy, clay, etc.) and the material you are using to amend the soil.

Lowering Soil pH (your soil is too alkaline)

There are a couple of good organic ways to get your soil’s pH level down. Assuming you have some time, mix naturally acidic matter into your soil in the fall such as:

  • Aged sawdust or wood shavings
  • Chopped-up pine needles
  • Peat moss
  • Shredded leaves

Caution

When spreading any fine particles, be sure to wear a dusk mask to prevent inhalation.

If your pH is still too high come spring time, you can mix in agricultural sulfur or iron sulfate, but this is only a short-term fix and should be followed the next fall with additional naturally acidic matter.

To add sulfur or iron sulfate to your garden, use a scoop to sprinkle it evenly over your entire garden in the amounts indicated below to lower loamy soil pH to 5.5.

Initial pH Sulfur Iron sulfate
7.5 5 lbs. (2.3 kg) per 100 square feet (30.5 sq m) 11.5 lbs. (5.2 kg) per 100 square feet (30.5 sq m)
7.0 3.5 lbs. (1.6 kg) per 100 square feet (30.5 sq m) 9 lbs. (4.1 kg) per 100 square feet (30.5 sq m)
6.5 1.5 lbs. (0.7 kg) per 100 square feet (30.5 sq m) 3 lbs. (1.4 kg) per 100 square feet (30.5 sq m)

Note: Clay soils will require heavier applications of pH-lowering amendment; sandy soils, less amendment.

Ref: University of Missouri Extension

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Raising Soil pH (your soil is too acidic)

Caution

When spreading any fine particles, be sure to wear a dusk mask to prevent inhalation.

If your soil is too acidic, there are a few ways that you can adjust its pH, some that are more complicated than others.

  • No professional testing: In the fall, till in ground calcitic limestone down at least as deep as your plants’ roots will grow. If you’ve got a nice, loamy soil, spread 5 pounds of lime for every 100 square feet to raise your soil’s pH by one point. The more sandy your soil, the less you’ll need. The more clay your soil has, the more you’ll need.
  • With professional testing: If you want to be more exact, have your soil tested by your local Cooperative Extension office or garden supply center. Their report will recommend specific materials and quantities to add to your garden.

    Depending on existing element levels and your soil’s textures, they will most likely recommend adding calcitic limestone, dolomitic limestone (for manganese deficiency) or wood ashes.
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