How to Balance the pH for Penstemon Plants

Balancing the pH for Penstemon plants is crucial for their growth and blooming. Penstemon plants generally prefer a slightly alkaline pH above 7.0, but this requirement varies with the species. To ensure your Penstemon plants thrive, follow these steps to balance the pH of your soil.

Soil Testing

Before planting Penstemon, it’s essential to test the soil pH to determine if it’s within the preferred range. You can purchase a soil testing kit from a local garden center or send a sample to a local extension service for testing. This will provide you with the current pH level of your soil, which is the first step in understanding how to adjust it.

Amending the Soil

penstemonImage source: Pixabay

If the soil pH is too acidic (below 7.0), you can amend it by incorporating pumice or ground oyster shell to raise the pH. This is especially important for species that require a slightly alkaline pH. The amount of amendment needed will depend on the current pH level and the desired target pH.

To amend the soil, follow these guidelines:

  • If the soil pH is between 6.0-6.5, add 2-4 pounds of ground limestone per 100 square feet of garden area.
  • If the soil pH is between 5.5-6.0, add 4-6 pounds of ground limestone per 100 square feet of garden area.
  • If the soil pH is below 5.5, add 6-8 pounds of ground limestone per 100 square feet of garden area.

Incorporate the limestone into the top 6-8 inches of soil, and then retest the pH after a few weeks to ensure it has reached the desired level.

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Mulching around Penstemon 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. Keep the mulch a few inches away from the plant stems to avoid rot and pest issues.


penstemon 2Image source: Pixabay

Penstemon plants do not generally require a lot of fertilizer. Over-fertilizing can lead to abundant leaf growth at the expense of blooms and might even harm the plants. If you choose to fertilize, do so in the fall to help boost their growth and flowering potential. Use a fertilizer low in nitrogen to avoid increasing the acidity of the soil.


Penstemon plants are drought-tolerant once established but will need regular water until they reach that point. Water newly planted penstemons regularly until they show signs of growth and are well-established. Once established, water them deeply but infrequently, allowing the soil to dry out between waterings. Avoid overwatering to prevent crown rot and decreased plant vigor.


Deadhead spent flowers to encourage continued blooming throughout the summer. In late winter or early spring, cut back the plants to about 4-6 inches (10-15 cm) above the ground to promote new growth and help maintain a tidy appearance.

By following these steps, you can balance the pH for Penstemon plants and provide them with the optimal growing conditions they need to thrive. Remember, the specific pH requirements may vary depending on the Penstemon species, so it’s essential to research the needs of the particular variety you are growing.

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  1. Penstemon: How to Grow and Care with Success
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  3. Penstemons are Colorful and Low-Maintenance for Garden