How to Balance pH for Penstemon Digitalis

Balancing the pH for Penstemon digitalis is crucial for the plant’s optimal growth and health. This perennial wildflower thrives in slightly alkaline soil with a pH range between 5.5 and 7.0. By following the steps outlined in this comprehensive guide, you can ensure your Penstemon digitalis plants receive the right soil conditions to flourish.

Soil Testing

The first step in balancing the pH for Penstemon digitalis is to test your soil’s pH level. This can be done using a soil test kit or by sending a soil sample to a local extension office or laboratory. Knowing the current pH level of your soil is essential for determining the appropriate amendments needed to achieve the ideal range.

Amending Soil pH

penstemon digitalisImage source: Pixabay

Increasing Soil pH

If your soil pH is below 5.5, you’ll need to raise it by adding lime to the soil. The amount of lime required will depend on your soil type and current pH level. As a general guideline, for every 1 point increase in pH, you’ll need to add 5 to 10 pounds of lime per 100 square feet of garden area.

Decreasing Soil pH

If your soil pH is above 7.0, you can lower it by adding elemental sulfur or sulfur-coated urea. The amount needed will depend on your soil type and current pH level. For every 1 point decrease in pH, you’ll need to add 1 to 2 pounds of sulfur per 100 square feet of garden area.


Penstemon digitalis generally does not require heavy fertilization. However, a light application of an organic fertilizer in the fall can help boost the plant’s growth and flowering. Avoid over-fertilizing, as this can lead to excessive foliage growth at the expense of flower production.

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penstemon digitalis 2Image source: Pixabay

Proper watering is essential for Penstemon digitalis. Water the plants well until they are established, then allow the soil to dry out between waterings. Overwatering or wet soils can lead to root rot, so it’s important to maintain a balance.


Applying a layer of organic mulch around the base of the Penstemon digitalis plants can help regulate soil temperature and suppress weed growth. Choose a mulch that does not hold water, such as shredded bark, compost, or pine straw. Avoid direct contact between the mulch and the plant stems to prevent rot and pest issues.

Monitoring Soil pH

After amending the soil, retest the pH level after a few months to ensure it has reached the desired range of 5.5 to 7.0. Continue to monitor the pH level annually and adjust as needed to maintain the optimal growing conditions for your Penstemon digitalis plants.

Remember, the specific pH requirements may vary slightly depending on the Penstemon digitalis species you are growing. Incorporating pumice or ground oyster shell can also help amend the soil for better growing conditions.

By following these steps, you can successfully balance the pH for your Penstemon digitalis plants, ensuring they thrive and produce vibrant, healthy blooms.


  1. Darwin Perennials – Penstemon digitalis Culture Sheet
  2. – Penstemon digitalis
  3. Colorado State University Extension – Growing Penstemons
  4. Clemson University – Penstemon digitalis (Foxglove Beardtongue)
  5. Greenhouse Grower – How to Grow and Sell Penstemon