Soil pH affects plants in a lot of different ways but it’s not always easy to identify when pH is the problem.

Whether it’s too high or too low, the signs are similar. Your plants aren’t growing as they should and it’s likely fertilizer isn’t working.

There are certain things to look for to determine whether soil pH is too high or too low so you can treat the soil as necessary and have happy, healthy plants again. Let’s take a closer look.

What is pH and Why Is It Important?

pH is the measure of how acidic or alkaline something is. Acidity is very important for all living things because most essential biological functions depend on having the right pH.

The pH scale runs from 0 to 14. The lower the number, the more acidic something is, the higher the number, the more alkaline it is.

For example, lemon juice is very acidic with a pH of about 2 whereas bleach is very alkaline with a pH of 13. Water is neutral with a pH of 7.

Acidity heavily influences absorption and solubility which is really important for plant growth. It also has a significant effect on the organic materials that are able to survive in the soil as well as how things like pesticides, metals, and contaminants are flushed out of the soil.

Is There any Way to Tell if pH is Too Low?

Soil pH naturally decreases over time if you don’t take care of it. It leads to an excess of aluminum and iron, deficiencies of potassium, phosphorus, and magnesium, and generally poor soil that nothing grows in.

While you should actively test your soil to be sure, there are some things to look for that suggest it’s getting too acidic.

If you notice that there are a lot of weeds in your yard and there didn’t use to be, you probably need to raise the pH. Some weeds and moss prefer acidic soil so if you start to see an abundance of them, it’s safe to assume the pH is low.

Low pH basically makes it really hard to grow plants. If you’re not sure what the problem is and fertilizer doesn’t seem to be helping, this could be an early sign that the pH is low.

Why? Because fertilizer depends on the right pH. If it doesn’t work, something’s definitely off.

The most definitive way to determine if your soil pH is too low is to have it tested. There are kits you can use to test it yourself at home or you can take a sample to a garden center or home improvement store and have them test it for you.

Raising pH

The best way to increase the pH in the soil is to apply lime, which is alkaline. Lime comes in a few different forms including pulverizer, granules, and pellets. Which one you should use depends on your soil.

Pulverized lime is so tiny that it’s very easily absorbed but can be difficult to spread evenly. Granules and pellets are easier to distribute but don’t have the long-lasting effects of pulverized lime.

There are liquid forms available but they’re not recommended. Because they’re water-soluble, they can be absorbed too quickly and raise the pH too much, too fast.

Another option is wood ashes which are literally the ashes of burned trees. Not only are wood asked alkaline enough to raise the pH, but they also add micronutrients like potassium, boron, and calcium.

Wood ash doesn’t work as quickly as lime in the short term but over time it can dramatically increase the pH. Be sure to monitor your soil carefully if you give wood ash a try.

Is There any Way to Tell if pH is Too High?

If the pH is too high, plants lose the ability to absorb certain nutrients effectively. If you notice yellow leaves, this is a good sign that your plants aren’t getting what they need. High pH can also cause toxicity in some plants because it allows certain nutrients to build up in the soil, poisoning the plants.

High pH is also likely to throw off the balance of microorganisms in the soil in part because creatures like earthworms don’t like alkaline environments. They stop doing the important work of converting nitrogen in the soil.

Specifically, high pH leads to high levels of calcium, iron, and phosphate and deficiencies in iron, phosphate, and zinc.

The best way to tell if the pH is too high is to test the soil. That’s really the only surefire way to determine what’s wrong and what you should do to correct it.

Lowering pH

There are a few things you can do to bring down soil pH. First, try adding organic material to the soil. You can use your own compost or buy composted manure. As organic material breaks down, bacteria digest it which creates acidic byproducts. These byproducts, in turn, bring down the pH.

Organic matter will work but it may take a little time. If you want something that works a little quicker, aluminum sulfate is another option. When it dissolves, aluminum sulfate is very acidic. It works rapidly but uses caution as it can be a little too effective.

Sulfur is another option. It’s less expensive than aluminum sulfate, more potent, and slower acting. Bacteria in the soil metabolize sulfur, eventually turning it into sulfuric acid which lowers the overall pH. It can take a few months to have a significant effect.

pH and Growth

It’s not always obvious if your soil pH is too high or too low but you will notice that your plants aren’t behaving as they should be. Maybe they’re not growing at all, maybe they’re turning yellow, or maybe there are weeds and mosses sprouting up all over the place.

If you’ve tried adding fertilizer and have had no success, pH is probably to blame. Fertilizer won’t work if the pH is too low because the acidic environment affects the absorption of the nutrients into the soil. If the pH is too high, the plants won’t be able to absorb anything.

The first thing you should do if you suspect a problem with the pH in your soil is to have it tested. That way, you’ll know exactly what you’re dealing with so you can come up with a plan to correct it.