Late fall gardeners are finishing and closing their gardens. Your winter rose care is complete, and the garden’s beautiful trees and shrubs have gone dormant. This is the time when we can give more attention to the indoor plants. Of course, the indoor plants have continued to be cared for. They’ve been watered and fed regularly but maybe not given the individual attention that there is now time to give.

Perhaps you have a houseplant that seems healthy but is not thriving the way you would expect. Maybe it is even giving signs that all is not well. It is time to look at the soil and check the pH.

What Is pH?

pH is a measurement of the level of acidity or alkalinity of the soil. The scale goes from 1 to 14, where most soil pH is between 4 and 8. Most potting soil starts at 7, which is considered neutral. Any reading below is acidic and any reading above 7 is alkaline. While many houseplants will do fine with a pH of around 6.5, there are some houseplants that prefer a more alkaline soil.  It would be no surprise at all to know that citrus trees prefer a more acidic soil as low as 5.5.

Minerals in the soil, which are the plant’s nutrients, are water soluble. The type and amount of mineral that will be dissolved is determined by the acidity of the soil. So, the pH is going to influence which minerals and how much of each is available for the plant to use.

Phosphorus is difficult for houseplants to absorb, but plants need phosphorus for photosynthesis. A lack of phosphorus will impact a plant’s ability to form roots and flowers. Chlorosis is another pH problem, especially for citrus trees grown indoors caused by a lack of iron. Usually there is enough iron in the soil, but it just isn’t accessible to the plant. The pH must be acidic to release the iron.

Every plant has a different pH preference and need, sometimes alkaline and sometimes acidic. As mentioned earlier, most houseplants will be fine with a pH of around 6.5. However, if you are trying to grow plants that are more sensitive to a certain pH level, signs of distress can include drying of leaf tips and edges, discoloration of leaves, stunted growth and a lack of blooms. Your plant can be damaged by too much of certain minerals — as well as too little.

4 Soil pH Tips for Indoor Plants

Now that you know what pH is and how its levels in the soil can impact your plant’s growth, here are 4 soil pH tips for indoor plants:

Know the pH Your Plant Prefers

Most plant labels will tell you what pH the plant desires, especially if it is more acidic or alkaline than most plants. A quick check on the Internet will also give you the pH information for any plant.

Understand the Effects of the Soil’s pH

Lots of things can affect the pH of your soil. Sometimes, the soil is intentionally changed. For instance, there are soil mixes that are made specifically for African violets, or succulents where the mixes are made to address soil composition such as fast draining or soil that will hold moisture. Many times, the soil is also going to be amended to bring the pH to the level which a particular plant type prefers.

Sometimes, the soil’s pH is affected unintentionally. Organic matter in the soil degrades the pH and acid rain can change the pH in the other direction. The type of fertilizer you apply can affect the pH of the soil as well as the type of soil itself — depending on whether it is clay-based or sandy. You need to understand the effects of all these factors related to the soil’s pH.

Learn Which Plants Have Special Needs

Most gardeners would answer that question with “All of them!” However, there are groups of plants that enjoy acidic or alkaline conditions. Succulents prefer alkaline soil where citrus trees, azaleas, hydrangeas, daffodils and camellias are acidic soil-loving plants. Overall, more plants like acidic soil than alkaline soil.

Determine How You Can Change the pH

The easiest and perhaps safest way to change the pH of the soil is to replace the current soil with soil of the correct pH for your plant. While this may cause some transplant shock, this method will eliminate calculations and the risk of over-correcting the current pH.

If the soil is too acidic, you can add horticultural lime to raise the pH. If your soil is too alkaline, the addition of horticultural sulfur will bring the pH down. You will have to consider how large the soil pot is and what type of soil is currently in the pot.

Be very conservative and add the lime or sulfur gradually and carefully. Each pot will need to be addressed individually. Retest the soil after a week to see if you have been successful or if you need to re-treat.

How to Test for pH

The best and most accurate way for a gardener to test their soil is with a pH meter or pH Test Kit. Follow the directions on your kit using soil samples collected near the root system of your plant. These test kits are very accurate if you follow the directions carefully. These kits can be used to test any soil, including your outdoor garden soil in the spring.

If you plan on adding new trees and shrubs to your landscape, it is always a good idea to check the pH of the soil when preparing the new site for planting. A good example of the impact of pH is the hydrangea bush, which can adapt to most soils but its flowers will be blue or pink depending on the pH of the soil it is grown in.

Following the four tips in this article will help you to test and optimize the pH in your soil for the types of plants you grow both indoors and in your outdoor gardens.