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Monday - January 16, 2012

From: Austin, TX
Region: Southwest
Topic: General Botany, Soils
Title: Changing the pH of the soil
Answered by: Nan Hampton, Barbara Medford and Joe Marcus

QUESTION:

Hi, We have a job that has mostly Texas native plants on it. The architect is wanting to drop the pH levels of the soils to acidic levels that we don't feel is good for the plants and the area. Could you please contact me so I can send you the plant list and get your recommendations for the soil pH for the various plants? Thanks.

ANSWER:

The soils in Austin/Travis County are highly alkaline and the native plants of our area thrive on this soil. So, the fact that the architect wants to acidify the soil says to me that he intends planting non-native cultivars or, at least, plants not native to this part of Texas. They will look beautiful for a short period of time until the pH of the soil begins to go up as the acidity of the soil declines—and it will definitely decline. The soil will gradually return to its original alkalinity, probably within just a couple of years, and the acid-loving plants growing there will begin to sicken and probably die. Additionally, acidifying the soil would likely have an adverse effect on the native microfauna living in it that are essential for healthy plant growth. The plants native to Central Texas are not going to do well in the acidified soil and the non-native plants that start out doing well are not going to do well for very long as the acidity weakens.

You will find that the majority of the plant species pages in our Native Plant Database contain a description of the soil requirements for the plant under the heading "Growing Conditions". For instance, on the pages for both Sophora secundiflora (Texas mountain laurel) and Cercis canadensis var. texensis (Texas redbud), under GROWING CONDITIONS, you will find: "Soil pH: Alkaline (pH>7.2)." You can search for the pH values of the native plants on your list in our Native Plant Database. It is easiest to search by the plant's botanical name. If the pH level isn't given for the plant you are looking for, then your best bet is to search the internet using the plant's botanical name.