Soil pH is one of the essential soil qualities you must consider when planning which plants to grow in your garden. Various plants have different soil pH requirements, and having the correct acidity or alkalinity can dictate what nutrients can be accessible to them.
Acidic soil doesn’t always contain more plant nutrients. Low pH can inhibit plant roots from absorbing some soil nutrients, like phosphorus, but can boost the availability of others, like iron and zinc. Finding a suitable pH level is necessary to ensure the nutrients are available at optimal levels.
This article will discuss what soil nutrients are accessible or inaccessible in acidic soil and how they can affect plant health and growth. I will also share how to improve the soil condition to protect your plants from nutrient toxicity or deficiency caused by soil acidity. Read on to learn more!
Nutrients Available to Plants in Acidic Soil
The nutritional content of soil primarily depends on its mineral composition. It is also affected by environmental factors like rain leaching the nutrients deep into the ground or the number of plants and soil microbes consuming them.
On the other hand, soil pH plays an important role in many chemical reactions that occur in the soil, including breaking down or transforming compounds into forms that can be easily absorbed by plant roots. It can also affect the microbial degradation of organic matter.
Such reactions are beneficial to plants because they allow plants to absorb many essential nutrients. However, most plants need only trace amounts of certain nutrients to thrive, and an excess can cause detrimental effects.
Let’s look at some of the nutrients that become widely available for most plants under highly acidic soil conditions:
Iron is an essential nutrient for photosynthesis to take place in plants. However, too much iron in the plant’s system can stunt growth and cause several other symptoms, such as the discoloration of leaves.
The toxic form of iron becomes readily available for root uptake at pH levels below 5.5. Acid-loving plants like blueberries have developed an adaptation that makes them resistant to iron toxicity.
Zinc is another nutrient plants can benefit from in low doses because it’s essential for several enzymatic reactions in plants. It becomes more available for plants at low pH levels and can become more inaccessible as the pH rises above 7.0.
In excess, zinc can stunt plant growth and negatively affect the plant’s respiratory rate.
Many plants with blue fruits or flowers like blueberries and hydrangeas owe their beautiful hue to the aluminum they absorb from the ground. This is only possible in highly acidic soil, which encourages plants to absorb aluminum.
Aluminum is abundant in soil. However, at pH levels above 5.0, the nutrient becomes almost entirely unavailable to plants. This limitation is beneficial to most plants because aluminum can inhibit root growth, which can be detrimental.
That’s why most plants prefer only slightly acidic soil with pH levels between 5.8 and 6.7. Those that thrive in a more acidic environment have likely developed a tolerance to aluminum toxicity.
Many enzyme activities in plants and their resistance to particular diseases are dependent on the availability of copper in the plant’s system. The nutrient is available for plant uptake at slightly acidic soil levels (5.5 – 6.5) and gradually declines as the pH rises over 7.5.
Manganese contributes to plants’ respiratory and photosynthetic functions. It becomes available for plants at pH levels between 5.5 and 6.5.
It can reach toxic levels and cause problems for plants when the pH drops below 5.0. Excessive levels of manganese in the plant’s system have an inhibitory effect on the plant’s ability to absorb other essential nutrients, such as magnesium and phosphorus.
Boron plays a vital role in plants’ cell walls and helps nitrogen metabolism. However, it is one of the nutrients that plants only need trace amounts of to survive. Toxic levels of boron in plants usually manifest through leaf discoloration and premature drops.
It is widely available in plants at pH levels between 5.0 and 7.0. Below 5.0, boron’s availability for plants gradually declines. Interestingly, boron becomes unavailable between 7.0 and 9.0 and increases its availability again as the pH level goes over 9.5.
Nutrients Can Become Inaccessible
There are also plenty of nutrients that can become inaccessible to plants under very acidic soil conditions.
It is important to note that the soil’s nutritional content is not directly affected by pH. Instead, the soil’s acidity can affect the nutrients’ availability for plant root uptake. Therefore, you can have plenty of nutrients in the ground, but they can be in forms inaccessible to plants due to high acidity.
Here are some soil nutrients inhibited from root absorption by high acidity levels:
As one of the big three nutrients for a plant’s overall development, phosphorus should be available in varying amounts throughout a plant’s growth. Soils rich in organic matter should have enough phosphorus, and availability is optimum when the soil pH is maintained between 6.0 and 7.0.
Plants can no longer absorb the nutrient at pH levels below 5.5 or above 7.5. The low levels of phosphorus accessible to plants can result in a significant decrease in the size of leaves and stems.
Potassium helps plants build up resistance against diseases and tolerate stressful conditions, making it one of the most essential macronutrients. However, its availability is greatly affected by soil pH, with the optimum range between 6.5 and 7.5.
Below 6.0, potassium’s availability significantly declines, and the plant becomes more susceptible to microbial infections and stress-related diseases.
Plants need calcium in their cell wall and cell membrane. It provides the cells support and facilitates their permeability to other nutrients.
It is highly accessible to plants in alkaline soils. However, calcium can become unavailable to plants when the soil pH drops below 6.0. As a result, the roots’ tips may die and the leaves will have dry tips. Various symptoms can occur in different types of plants.
Magnesium plays a significant role in photosynthesis because it is one of the most essential components of chlorophyll. Needless to say, magnesium deficiency can negatively affect a plant’s growth and halt several biological processes.
Like phosphorus, magnesium is also unavailable for root uptake when soil pH levels are below 5.5.
What Is the Ideal Soil pH for Plant Nutrient Availability?
Plants generally have an ideal pH range wherein they can thrive, but most known plant species prefer a pH range between 6.0 and 7.0, which allows them access to many essential soil nutrients.
Therefore, it’s crucial to understand your plant’s traits and growth requirements to provide it with the most suitable growing environment. Luckily, it is possible to amend your soil to make it conducive to plant growth.
However, suppose you are considering making significant adjustments in soil pH (over 0.5). In that case, you might as well purchase a substrate with your desired pH. Changing and maintaining the soil at a pH level very different from its nature can be costly and troublesome.
For minor adjustments in pH, you can refer to the ideas below:
Add Lime to Reduce the Acidity
Various nutrient toxicity or deficiencies can occur in highly acidic soil. To raise your soil pH to safe levels, you can add lime or wood ash. However, be careful about how much you add, as these materials are highly alkaline.
Finely ground lime can raise the pH more quickly but may still require at least one season to show considerable changes.
Use Sulfur to Raise the Acidity
Sulfur can lower the soil pH to cater to many acid-loving plants. However, it can take several months to reduce it to suitable levels if you’re planning to grow pine trees or rhododendrons.
It can also be challenging to maintain the soil at very low pH levels. Many factors can affect how quickly and effectively you can raise the soil’s acidity, such as the size of the area, the climate, and the porosity of the soil particles.
Although soil acidity doesn’t directly affect the number of nutrients present in the soil, an extremely low pH can dictate how many and how much of these nutrients can be absorbed by your plants’ roots.
Therefore, it helps to pay attention to your plant’s nutritional requirements and soil acidity preferences to ensure it can access the nutrients it needs.