Does Sunlight Affect Soil pH? A Simple Answer

When it comes to a plant’s ability to grow, several factors impact how and when a plant is likely to grow. One of these factors is the pH of the soil the plant is growing. With many factors impacting a soil’s pH, you might ask: Does sunlight affect soil pH?

Sunlight does not impact soil pH. pH is a measure of hydrogen ions in a substance, meaning pH is a chemical property of the soil. While climate, mineral content, and soil texture impact the chemical properties of the soil, exposure to ultraviolet light (such as sunlight) won’t change pH.

Understanding a soil’s pH can ensure your plant grows. However, it can be somewhat confusing to understand at first. Let’s take a deeper look at what pH is, how it works in soil, its impacts on plant growth, and how some factors can alter a soil’s pH.

pH Explained

Imagine cleaning your car and finding a bunch of quarters and pennies stuck between the seat cushions. Chances are, these coins are very dirty, and you want to clean them off before using them. You grab your vinegar or lemon juice, slowly rub it on the coin, and notice something: after a while, the penny is clean as new! Why is that?

Your penny’s exterior dirt and grime just underwent a chemical reaction that caused it to clean off. The vinegar has a high number of hydrogen ions, that is, hydrogen particles that have a very slight charge. In chemistry, these particles always want to try and achieve a neutral charge, meaning these charged particles want to mix with oppositely charged particles to make a compound (a combination of chemicals) with no charge. 

The vinegar has such a high number of these charged particles that it can react with the stuff on the outside of the penny to make it clean. Alternatively, nothing would happen if you put this dirty penny in the water. That is because water does not have a charge. That means it will not interact with the penny to clean it.

Outside of our science experiment, however, the same ideas remain. When explained in its most basic way, pH is just the concentration of these hydrogen ions in a substance. Substances that have a higher concentration of these hydrogen ions have a lower pH, making them “acidic.” But substances with a lower concentration of these hydrogen ions have a higher pH, making them “basic.”

pH in Soil

With this rudimentary understanding of pH, we can now apply the concept of pH to the soil. Soil is not just a speck of perfect dirt. Soil is made from a combination of minerals, air, water, and organisms. That means the soil is made up of substances with different concentrations of hydrogen ions. Imagine, for example, pouring vinegar into the dirt; in this instance, you’d have very acidic soil.

Such being true in the case of acids, the inverse is correct as well. If you were to pour a bottle of ammonia onto a patch of dirt, that dirt would then become incredibly basic (it would have a low concentration of those hydrogen ions). However, while these examples make it easy to picture how soil might have these changes in pH, these are not nearly how stringent the requirements are for changing soil pH.

Take, for example, a garden that has compost in it. Compost is made of organic matter that will break down over time to provide the dirt with the nutrients once found in that natural material. As these materials break down, they produce carbon dioxide. If the compost is very wet, however, not all of the carbon dioxide will escape into the air, and some will remain in the water found in the soil. It can create a slight charge to the water, thus making the soil basic.

Alternatively, if you wanted to make your soil slightly more acidic, you could add sulfur to it. When the sulfur mixes with water in the ground, the neutrality of the water will interact with the charge of the sulfur to make a slight change, creating sulfuric acid.

Soil pH and Plant Growth

Like animals in nature, different kinds of plants thrive in different types of environments. Just like how you can’t place a penguin in the Sahara Desert, you can’t simply move a cactus to a rainforest. These plants—over their development—have grown to thrive in certain conditions. One of these conditions plants have adjusted to is soil pH.

Some plants, such as Pine Trees, Hemlock Trees, and Dogwood bushes, have adapted to thrive in acidic soil. Other plants, like Lilacs, Mums, and Asparagus, like particularly basic soil. These preferences most often come from the nutrient types these plants need. When these different nutrients are in the soil, they mix with the water and the other substances in the soil to create acidic or basic substances that impact plant growth.

Unfortunately, this preference also creates a high vulnerability for many plants. If, for example, you wanted to plant something that typically grows in acidic soil and the soil near you is not, then you would need to adjust the soil’s pH for the plant to grow. While adding the required nutrients to the soil would help adapt the pH level, you might also need to add specific particles to change the pH.

Ultimately, how a plant grows in specific types of pH is determined by that plant’s needs and preferences. Unlike many other predictions that can be made when it comes to plant growth, a certain level of pH can not perfectly predict a change in the level of growth and resilience a plant has. These will depend on the pH level and the plants’ preferences.

Factors Impacting Soil pH

While sunlight does play a large role in the development of a plant, it plays a very minute role in determining a soil’s pH. The sunlight and the ultraviolet rays it produces may create a chemical reaction when shined upon different materials. But it generally does not impact the substance’s concentration of hydrogen ions. 

Other factors, however, can play a big role in determining the pH of the soil. 

One major factor, for example, is the amount of water the soil receives. A large amount of water can limit the concentration of hydrogen ions in a substance, thus diluting the substance’s acidity. Water can also wash out some of the chemicals that are helping to impact the pH in the soil, causing a change.

Another factor that can influence soil’s pH is the mineral composition of the soil. As mentioned previously, if a soil has a high amount of a specific mineral that contains a high number of hydrogen ions, that soil is prone to become more acidic. If the soil has a material that absorbs or lowers the concentration of the hydrogen ions, then it will likely have a lower pH.

Soil texture can also be a major factor that can influence soil’s pH. Soils with high amounts of clay or organic matter can make changes in pH harder to occur. If soil is incredibly sandy, however, it is much more susceptible to changes in pH.

Sunlight Can Affect a Plant’s Growth

As discussed, sunlight does not affect a soil’s pH. So whether the sun is bright or not, its sunlight won’t impact the soil’s pH. However, the sun can have effects on the growth of the plants growing in the soil. Plants rely heavily on the climate, water, and the organisms that help the soil in which they grow to thrive.

But as this article emphasizes, sunlight does not affect a soil’s pH. So if your plants didn’t thrive, it wasn’t because the pH of the soil they grow in was affected by sunlight. 

Final Thoughts

While sunlight does not impact a soil’s pH, many other factors can. The water amount the soil receives, the mineral composition of the soil, and the soil’s texture all can be factors that have a major impact on the concentration of hydrogen ions in the soil.

Ultimately, plants all operate in different ways when exposed to varying pH levels. While some plants do incredibly well in acidic soil, others do poorly. Making sure that the soil you use is compatible with the plant’s growth and adjusting the soil’s pH as necessary will give the best chances for your plant’s survival.

If you want to learn more on the reasons why soil ph is so important, you can read my other article here: 5 Reasons Why Soil PH is So Important

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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