Soil pH is an important and frequently overlooked factor in gardening and agriculture. It dramatically impacts plant health and can be the difference between a thriving ecosystem and a garden with plenty of room for improvement. The pH of the soil impacts nutrient uptake, microbial activity, and more. This article will explore the details of soil pH, why it’s important, and how to alter it.

The Fundamentals of Soil pH

Soil pH is a number that indicates how acidic or alkaline (basic) something is. It can be applied to anything, not just soil! The numbers lie on a scale from 1 to 14, with 7 being neutral, below 7 being acidic, and above 7 being alkaline. The vast majority of plants prefer somewhere between 6.0 and 7.0, but some plants have more specific needs.

Soil pH influences plant health, with the most severe consequences experienced when pH is radically out of the preferred range. Soil pH impacts nutrient availability and uptake for plants. For example, nutrients such as nitrogen, phosphorus, and potassium become less available to plants if the soil pH is too high or too low. Iron, manganese, and phosphorus are more available in acidic soils, and calcium and magnesium are more available in alkaline soils. Soil microorganisms, which are essential for soil and plant health, are also impacted by pH. Acidic or alkaline soils can suppress these beneficial organisms, leading to poor soil health.

Plants adapted to specific pH conditions will struggle to absorb nutrients if the soil pH is outside their preferred range, leading to stunted growth, poor flowering, and lower yields. For example, blueberries, azaleas, and camellias all prefer more acidic soils (5.0-6.0), while lavender, clematis, and asparagus thrive much more readily in alkaline soils (6.5-7.5). A few decimals can impact nutrient availability and mean a struggling blueberry crop or reduced asparagus yields.

How to Check Soil pH

So, how do you know if your soil pH is off? The most accurate way to know this is by testing it. You can use a soil pH test kit. Or, if you send a sample of your soil to a local agricultural extension service for professional testing, they will tell you a whole host of information, among which will be the pH.

However, there are a few tried and true indicators that the plants will display as they try to tell you something is off in the soil. Yellowing leaves are a sign of iron deficiency in plants like azaleas and rhododendrons, often due to soil being too alkaline. Vegetables like tomatoes and peppers may show poor growth if the soil is too acidic or too alkaline. Plants such as clematis and roses may not flower well if the soil pH is not optimal. Also, generally speaking, consistent poor performance across various plants may indicate an overall imbalance, especially if you have tried other things to remedy the situation.

How to Increase Soil Acidity

The three most common amendments often added to soils to increase acidity include elemental sulfur, aluminum sulfate, and organic matter. Elemental sulfur is a common amendment for lowering soil pH. When applied to the soil, sulfur is converted to sulfuric acid by soil bacteria, which acidifies the soil. It’s best applied in small amounts and mixed thoroughly into the soil. Aluminum sulfate reacts quickly with the soil to lower pH. However, it should be used cautiously, as excessive amounts can be toxic to plants.

Organic matter said to increase soil acidity, but it requires more time and materials than the above-mentioned options. Nevertheless, adding pine needles, peat moss, or homemade compost can help lower pH (increase acidity) over time. These materials decompose and produce organic acids, which gradually impact the soil’s pH. However, this is an uphill battle as the soil will naturally buffer this change. Many people will also opt to plant their acid-loving plants at the base of pine trees to naturally use this symbiotic relationship with minimal effort.

How to Decrease Soil Acidity

You also have options for raising the soil's pH to become more alkaline (decreasing acidity)! The three most common amendments used for this purpose are agricultural lime, wood ash, and bone meal. Agricultural lime (calcium carbonate, aka limestone) and dolomitic lime (calcium magnesium carbonate) are the most used for this purpose. These compounds neutralize soil acidity as well as add calcium and magnesium to the soil for the plants to use. It should always be applied according to specific recommendations and thoroughly mixed into the soil.

Wood ash is readily available and easily found. If you have a fireplace or fire pit, look no further! Ash raises soil pH due to its high calcium carbonate content. However, it should be used sparingly to avoid nutrient imbalances. Lastly, bone meal can be made or purchased, and due to it being a source of phosphorus and calcium, it can help raise soil pH. It’s especially beneficial for flowering plants and root crops.

Tips for Amending Soil pH

I always recommend getting a soil test done if you’re feeling unsure about what your garden needs. There are so many factors that contribute to plant health and soil alone holds the key to many of these issues. When amending soil, make applications at the beginning or during the growing season to encourage the microorganisms to be active. Amend and retest every couple of years for the most accurate results. Lastly, when using store-bought amendments, always follow the manufacturer’s instructions by wearing the indicated protective gear and avoiding over-applications.

When in doubt, your local extension office is a great resource for information specific to your region. Soil pH is not as complicated as it may seem! A few amendments here and there can keep your garden functioning at full capacity. Whether you are growing blueberries, clematis, hydrangeas, or asparagus, the soil’s pH will impact your garden. Understanding a few simple tricks can really up your gardening game this year!

Additional Resources:

• Utah State University - Solutions to Soil Problems II. High pH
• University of Arkansas - Prepare Your Garden | Soil Testing, Preparation, and Amendments
• Clemson University - Changing the pH of Your Soil

Lara Wadsworth, True Leaf Market Writer

I am a native of Southwestern Michigan, where I also reside, and I love all things plants! I got a Bachelor's Degree in Horticulture and found the first work-from-home job I could get. Now, I spend my days writing for TLM, playing with my dog, eating delicious food with my husband, and plotting my next landscape or gardening move. I believe everyone should get down and dirty in the soil now and then. Happy Gardening!