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If you’re a gardener, you know how much time and effort goes into caring for your plants. They need water and fertilizer to keep them growing healthily. But did you also know that the pH level of your soil can affect the way plants grow? 

When soil pH is too low (acidic), plants can have trouble absorbing nutrients through their roots. This may lead to stunted growth, yellow leaves, or a lack of flowers on the plant.

Plants can be affected by low pH levels. People pay lots of attention to the way they water their plants, but they don’t give much thought to the pH of the soil. If you have ever experienced a sickly-looking vine or shrub, you may have wondered what you were doing wrong. Read on to discover the importance of soil pH and how to spot if your soil may be too acidic.

Signs of low pH in plants

Plants grown in excessively acidic soil are likely to have several problems, including poor growth and nutrient deficiencies. In addition, plants can exhibit yellow leaves, few flowers, and stunted growth.

pH is a measurement of how acidic or alkaline a solution is.

It is measured on a scale of 0 to 14, with pH 7 being neutral. 

A low pH means the solution contains more acid, while a high pH means it contains more base.

If you’re worried about your plants’ pH levels, check for the following signs:

Leaves become yellow or have brown spots.

Leaves wilt or turn brown.

The leaves curl up and appear dry.

Plants are stunted and don’t grow as tall as they should be.

Most plants prefer a slightly acidic environment, with a pH between 5 and 6.5. 

Low pH levels can be caused by the addition of too much sulfur or nitrogen-based fertilizer, as well as by high acidity in the water used to irrigate the plants.

Effects of low pH in plants

The effects of low pH in plants can be devastating, as it can lead to a reduction in growth, nutrient deficiency, and even death.

One major problem with acidic soil is the presence of toxic metals, such as aluminum and manganese.  

These metals are more soluble in soil that has a lower ph, therefore acidic soil is likely to have a greater concentration of them. 

The amount of aluminum is 1000 times greater in soil with a pH of 4.5 than it would be at 5.5. 

Excess aluminum can cause plant roots to stop growing. This results in them being unable to absorb nutrients and water, leading to stunted growth. 

Causes of low pH in soils

There are a few different causes of low pH in soils, including nitrates and acid rain.

The most likely cause is the presence of high levels of nitrates, which can cause an increase in the acidity of the soil. 

Acid rain is another common cause of low pH in soil

Acid rain can be produced by the burning of fossil fuels, but it can also come from natural sources such as volcanoes. 

The main components of acid rain are sulfur dioxide (SO₂) and nitrogen oxides (NOₓ). 

These chemicals react with water in the air to form sulfuric acid and nitric acid.

Low pH plant symptoms

At low pH levels, important nutrients such as calcium, magnesium, and phosphorus can be lacking.

Magnesium is the central atom in chlorophyll, the chemical which gives plants their vibrant green color and allows photosynthesis to take place.  

If magnesium is lacking, the first symptom is often leaves turning from green to yellow. 

Eventually, they may turn red, purple, or brown, and the plants may die.

Learn more about photosynthesis 

Low ph can also lead to a higher uptake of iron and manganese, leading to burnt and speckled leaves. 

Low pH plant symptoms can be hard to spot, but they can really affect your plant’s growth and health.

If you notice any of these symptoms, you should check your plant’s pH level:

  • Pale leaves or yellowing leaves
  • Brown spots on leaves 
  • Stunted growth

What plants like low pH

Plants that prefer low pH are those that grow in soils that have a high concentration of hydrogen ions. These plants include azaleas, blueberries, rhododendrons, and camellias.

Gardeners often refer to these plants as “acid-loving,” but it’s not really acid these plants love. 

Instead, they are actually seeking the nutrients that the acidic soil provides.

Another tip for making the most of acidic soil, is for changing the color of one particular plant! 

Hydrangeas are the only plant that change color depending on the pH of the soil.  

The flowers will turn blue when planted in soil with a pH around 5, whereas they will be pink in more alkaline soil. 

If you have a patch of garden with acidic soil, take the opportunity to add some blue hydrangeas to your flower display.

Learn how to lower soil pH

The effect of soil pH on plant growth

The most important thing to know about soil ph is that it affects the amount of nutrients plants can absorb from the soil.

In the garden, soil pH is a measure of how acidic or alkaline your soil is. 

A pH level of 7 is neutral; everything below that is considered acidic and everything above it is considered alkaline.

Plants grow best in slightly acidic soil, with a pH between 5.5 and 6.5. 

If they were to grow in an environment with a pH higher than 7, they would have trouble absorbing nutrients from the soil and their growth would be stunted. 

On the other hand, if the pH was much lower than 6, plants would have trouble absorbing nutrients from their environment and wouldn’t grow as well either.

The soil pH can also influence plant growth by its effect on the activity of beneficial microorganisms

When the pH is low, the activity of soil bacteria is decreased. 

This prevents organic matter from breaking down and results in an accumulation of organic matter, which ties up nitrogen that is held in the organic matter.

How to raise soil pH

If you want to raise the pH of your soil, there are a couple of things you can do. 

The first is to add lime. Note that lime for soil does NOT refer to limes (the fruit), but to lime, which is a powder or solid substance that can be added to soil to raise its pH. 

Lime will raise the pH by removing some of the acidity from your soil and releasing calcium carbonate, which gives your soil a higher pH. 

This can be done by adding lime directly to the soil or watering with a solution of water and lime (be sure not to overdo it).

Baking soda is another easy and cost-effective way to raise the pH of soil.

Mix a tablespoon of baking soda with a gallon of water and add to your soil.

Learn how to use baking soda effectively in your garden

Final thoughts

Keeping your soil at the correct pH is important for healthy plants. Learning to spot the symptoms of acidic soil means you can correct any issues quickly and give your plants the chance to thrive.

Greg Volente

Greg Volente holds a Naturalist Certificate from the Morton Arboretum, worked for The Nature Conservancy leading environmental education programs and doing natural areas restoration, and worked in the soil science research & testing lab at Michigan State University. Besides gardening, he's an avid wildflower enthusiast, and loves botanizing, hiking, and backpacking.