how to lower soil ph in potted plants

How To Lower Soil pH in Potted Plants

Nutrients and minerals in the soil need to be dissolved before plants can absorb and use them. The soil pH affects how easily the nutrients dissolve in the soil where they then become available for your plants. Most minerals and nutrients are readily available to your plants when the soil pH is between 6.0 and 7.0. However, a slightly acidic soil pH between 5.0 and 6.5 is ideal for most houseplants, says the University of Georgia Extension.

How do I know if my potting soil pH is too high?

The only way to accurately determine the soil pH in your plant’s soil is to test it. Inexpensive soil tests (like this one by Luster Leaf) for the garden can be used to test the soil pH in your houseplants. These simple kits contain vials and powdered additives to use for each nutrient, as well as the pH of the soil. Adding the appropriate additive (included in the kit) to water and a small soil sample will measure the soil pH. Results are typically interpreted by matching the color of the solution to an enclosed chart. Soil pH ranges from 0 to 14. A pH of 7.0 is neutral while numbers below 7 indicate acidic soil and numbers above 7 indicate alkaline soil.

You can also purchase a pH meter to measure the soil pH in your plant pots. PH meters measure the soil pH via a metal probe inserted into the soil. The results are displayed on the dial of the probe. A pH meter is easier to read than pH tests that require you to match the color of the water to a color chart to determine the pH.

What are the signs my potting soil’s pH is too high?

While a soil test is the only definitive way to tell if your soil’s pH is too high, there are some signs to watch for. If you notice any of these symptoms in your plants, there is a good chance your plants aren’t getting the nutrients they need because the soil pH is too high.

  • Yellowing between the veins on leaves.
  • Browning or dying leaf tips, especially on new leaves.
  • Stunted, distorted, or wilted leaves.
  • Brown spots on the leaves.
  • Deep green leaves with hints of purple, bronze, or red.


Measuring the pH of the existing potting soil

Inexpensive garden tests will generally give you a rough idea of the soil pH. Because they are designed to be used with multiple samples of soil taken at a depth of several inches that have been mixed together before testing, they may not be the most effective way to measure the pH in a relatively small sample of soil. Simply testing the soil at the top of the pot may provide misleading results.

A pH meter will likely give you a more accurate result as you can insert the probe to the root level to assess the soil pH.

What’s the easiest way to adjust the soil pH in houseplants?

You can certainly make efforts to adjust the existing soil’s pH, but when it comes to houseplants or plants grown in small containers, the easiest and most efficient method to adjust the soil pH to the desired level is to simply replace the existing soil.

Most commercially available potting mixing has a pH between 6.0 and 7.0, making them suitable for nearly all houseplants, but they can vary.

  1. Remove the plant from the existing pot.
  2. Remove the soil from the roots with your hands, or give it a gentle shake.
  3. Rinse away any remaining soil with the sink sprayer.
  4. Fill the pot one-half to three-fourths full of the new potting mixture.
  5. Position the plant into the soil, so the roots are spread over the new soil, and the crown of the plant (the area where the roots meet the stem) rests at the soil level.
  6. Fill in around the roots with fresh soil.
  7. Firm the soil in place around the roots to remove air pockets and provide adequate support for the plant.


What can I add to my potting soil to make it more acidic?

According to the New Mexico State University (NM State), you can mix two or three tablespoons of vinegar with a gallon of water and use it sparingly to make your potting soil more acidic. Many users advise spraying the solution on the top of the soil or applying it with a watering can. Care must be taken not to get the vinegar solution on the foliage or stems as it can damage plant tissues. In fact, NM State warns that the vinegar and water solution can harm your plants if it is too strong.

Other options include mixing peat moss into the existing soil as peat moss is naturally acidic.

peat moss compost is naturally acidic
Peat moss compost is naturally acidic.


How to lower soil pH in potted plants?

If the soil pH is above 7.0 in your potted plants, it may be too alkaline for them to get the nutrients they need to thrive. Lowering it to between 5.0 and 6.5 is desired. To do this, you will need to add a source of acidic material. Two common remedies for lowering the pH in the soil of houseplants are treating the soil with a mild vinegar and water solution or adding peat moss to the soil mix. Both will lower the pH of the soil and make minerals and nutrients more readily available to your plants.


How long should I wait before measuring the soil pH afterward?

Both peat moss and vinegar work relatively quickly to lower the soil pH in potting soil mixes. Measuring the pH level in a week or two should give you accurate results.

Summary

Adjusting the pH level in soil in potted plants can be accomplished either by changing the soil pH by adding peat moss or using a vinegar and water solution or by replacing the soil completely. Replacing the existing soil is typically easier and doesn’t require guesswork as to how much is enough. Generally, if you have a large difficult to repot plant or have a plant that is finicky about repotting, adjusting the pH with peat moss or vinegar and water may be the most efficient solution. However, most houseplants respond well to repotting and thrive with fresh soil. All you need to do now is get it done! Good luck.

If you feel like you need something even faster acting than vinegar or peat moss -see my article How to lower pH in soil fast -for even more suggestions.

Further reading:

https://aces.nmsu.edu/ces/yard/archives/april-16-2011.html

https://extension.uga.edu/publications/detail.html?number=B1318&title=Growing%20Indoor%20Plants%20with%20Success

https://blog.bluelab.com/signs-that-your-plants-are-struggling-with-incorrect-ph