Signs Of Low pH In Plants

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Low pH can affect your plant’s growth and survival. If your plants are showing stunted growth, yellow leaves, or leaves with brown spots or reddish-purple edges, then it is showing signs of low pH conditions. 

Growing plants or your own produce promotes good health and wellbeing; we are naturally drawn to plants because successfully growing a seed into something beautiful makes us feel good. 

Potential hydrogen (pH) is one of the most fundamental parameters when successfully growing plants. While other parameters such as temperature, humidity, and conductivity play an important role in your plant’s health, it is the pH of the soil that determines if your plant is receiving the right amount of nutrients needed for growth and survival. 

Today, we’ll cover why pH is important for your plants and what to look for if you are struggling with a pH that is too high or too low. 

Why Is pH Important?

The pH scale tells you if something is acidic or alkaline (basic), running on a scale from 0-14, with anything above 7 being alkaline, and anything lower than 7 acidic.

Plants need water and nutrients to grow, thrive, and survive, so maintaining the correct pH level in the soil (or water system) ensures your plants are receiving enough nutrients. 

I know what you are thinking… How is pH linked to nutrient availability?

Well, different nutrients are available at different pH levels. For the nutrients to become available for your plants, they need to be in nutrient ion form. Each nutrient ion has a preferred pH range to become available; thus, pH plays an important role in accessing vital nutrients such as nitrogen, phosphorus, and potassium.

So, it is also important to monitor the pH to prevent sticky situations known as “nutrient lockout”. If this happens, your plants will be unable to uptake the nutrients they need. 

Additionally, low pH can influence the structure and breakdown of organic substances and microorganisms that benefit your plant, reduce your plant’s water uptake, in some plants inhibit CO2 assimilation, and cause oxidative stress and electrolyte leakage. 

What Causes Low pH In Plants?

Many factors can affect the pH of a solution or soil. These include the following:

  • Pollution
  • Water irrigation
  • Fertilizers: When these break down, they release hydrogen ions into the soil, lowering the pH
  • Climate change 
  • Weather
  • Organisms
  • Geology
  • Topography
  • Algae growth
  • Carbon dioxide (CO2)
  • Nutrient toxicities (hydrogen, aluminum, and manganese)
  • Lack of nutrients (phosphorus, calcium, magnesium, potassium, and molybdenum)

What Happens To Plants If The pH Is Too Low?

A low pH creates an acidic environment, and while many plants thrive in slightly acidic environments, you should not let the pH of the solution or soil become too low, as this could lead to detrimental effects on your plants. 

Some nutrients may be available in low pH environments, while others become unavailable, causing nutrient deficiencies for your plant. Naturally, the pH of your soil or hydroponic system will fluctuate, which is another reason why it is important to keep on top of measuring the pH. 

Sometimes you may need to raise the pH level if it has become too low for your type of plant. The best way to check if the pH is too low is to use a pH meter. However, there are some physical signs you can also look out for. 

Signs Of Low pH In Plants

If your plants are experiencing a low pH environment, they may display one or more of the following signs:

  • Stunted growth
  • Brown spots on the leaves (calcium deficiency) 
  • Dying leaves
  • Green leaves with red or purple edges
  • Burnt tips (nutrient overload)
  • Looking withered 
  • Twisted leaves
  • If your plant has fruits, you may see blossom end rot
  • Yellow leaves, known as leaf chlorosis

Low pH & Nutrient Deficiencies

Nutrient deficiencies are the most common issue with low pH in plants. As mentioned, nutrients play a vital role in your plant’s health; nutrients are required for your plants to germinate, grow, reproduce, and fight off pests and diseases. When the pH is too low, the following macronutrients become depleted, leading to deficiencies. 

Nitrogen Deficiency

Nitrogen is a key component of your plant’s proteins. When the pH is low, it causes the plants to yellow at the bottom, and it inhibits growth. Nitrogen is also required to form chlorophyll, which is essential for your plant to photosynthesize, therefore low pH also affects enzyme reactions and your plant’s metabolism. 

To fix the issue, add a nitrogen-specific additive if you are running a hydroponic system, or for soil-based plants, you can add compost or manure. 

Phosphorus Deficiency

Phosphorus deficiency is linked to low pH levels in your soil and plant exposure to extremely cold conditions.  

Phosphorus deficiency is easy to detect as the older leaves on your plant will be affected first, turning dark green with purple or red edges. If left untreated, your plant will experience stunted growth and the leaves will eventually develop brown spots and necrosis. 

Phosphorus additives like superphosphate or phosphate rock are both great fixes. Nutrient solutions and fertilizers should be avoided, as they can oversupply your plants with nutrients. 

Potassium Deficiency

Potassium is important for water uptake and aiding photosynthesis. 

If your plant has chlorosis and brown or burnt-looking leaves, then it could be your low pH is causing potassium deficiency in your plant. 

In extreme cases, purple spots can form under the leaves, and if left untreated, potassium deficiency can cause slow growth and leaf necrosis. 

Potassium-rich additives such as seaweed, kelp, or tomato feed can be added to the soil to solve the issue. 

Calcium Deficiency

Calcium is the most important macronutrient for plant cell formation and development. Low pH in plants can strip calcium causing withered, and rather sad-looking leaves. Eventually, your plant will drop all its flowers as a response, and if you have a fruiting plant, the fruits will develop small, or any developed fruits will start dying. 

To treat calcium deficiency in hydroponics, only use a water-soluble calcium additive to prevent overdosing, and for soils, any form of lime will work wonders. 

Plants That Thrive In Low pH Environments

Testing the pH of your soil is important, but if the soil is naturally acidic, then you may want to consider adding plants that thrive in low pH conditions. 

Some plants grow well in acidic conditions. These include:

  • Blueberries and cranberries: pH of 4.5-5.5
  • Japanese iris: pH of 5.0-5.5
  • Barley: pH of 5.2
  • Timothy: pH of 5.5
  • Wheat: pH of 5.2-5.4

So, let’s say that every plant has its own “sweet spot” depending on what you are growing. For example, hydroponics (growing plants without soil) require a pH of 5.8-6.5, and growing plants in soil usually requires a pH of 6.5-7. 

However, as previously mentioned, the pH ranges vary between plants, so always do some research before diving into planting your harvest. 

What Happens To Plants If The pH Is Too High?

When the pH is too high, the environment becomes alkaline. Some plants will tolerate alkaline conditions, but others will not, leading to potential issues such as:

  • Brown spots on leaves
  • Leaf chlorosis
  • Tip death
  • Stunted and/or wilted leaves
  • Green leaves with red or purple edges

As you may have noticed, some symptoms of a high pH environment are similar to signs of low pH in plants, which is why testing the pH is essential in hydroponics and soil-based growing. 

How To Test pH In Plants?

To reliably test the pH in your soil or hydroponic system, we recommend using a pH probe/sensor. If you are unsure how to use a pH kit, then take a look at our guide on how a pH probe works. Also, if it is the first time you have used a pH kit, don’t forget to calibrate the pH probe

You can also use pH testing strips. However, the dependability of the results will be based on how well you can match the color on the litmus paper to the testing kit. pH paper strips also only give you a value, not a specific pH number like a pH probe

How Do You Adjust Soil pH?

If, after testing your soil or solution, the pH is outside your plant’s range, then the good news is that you can usually easily correct it. 

If the pH is too low, a lime application, baking soda, or a component high in calcium like eggshells can be added to increase the pH in the soil. 

If the pH is too high, adding an acidic treatment such as sulfur, aluminum sulfate, or sulfuric acid will buffer the pH level.

When adjusting the pH, always do it slowly and measure the pH level after each treatment to prevent unnecessary fluctuations. 

Summary 

Monitoring pH when growing plants is an invaluable tool for maintaining a healthy garden because low pH in plants can cause nutrient deficiencies, reduced harvest, and slower growth. 

When plants become exposed to low pH environments, they exhibit signs such as yellow leaves, leaves with brown spots, stunted growth, withered and/or twisted leaves, and leaves with red or purple edges. 
If you have any questions regarding pH or what pH probe will best suit your needs, do not hesitate to contact our world-class team at Atlas Scientific.

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