If you are a gardener or farmer, you’ve probably read a lot about how important it is to get the right pH level in your soil. You’ve probably also wondered what happens if you fail to maintain the right pH levels. I did some research to find out exactly what happens and why.
So, what happens to plants if soil pH is too low (or too high)? When soil pH is too low (acidic) or too high (basic), plants will have difficulty absorbing nutrients through their roots. The resulting nutrient deficiencies may cause problems including yellow leaves, stunted growth, or lack of flowers and fruit on plants.
Of course, each plant has its own ideal pH range, and some can survive or thrive in somewhat acidic or basic soil. Let’s start off by going into detail about how and why soil pH affects nutrient absorption for plants. Then we’ll talk about ways that you can treat low or high soil pH, along with ways to stabilize the pH once it is at the right level.
What Happens To Plants If Soil pH Is Too Low (Or Too High)?
Remember that pH is a scale from 0 to 14 that tells us how acidic or basic something is. Acidic means a pH less than 7.0, basic means a pH greater than 7.0, and neutral means a pH of 7.0.
When soil pH is too low or too high, plants have difficulty absorbing nutrients from the soil. The reason is that each nutrient has an ideal range where it is highly available to plants. Outside of this range, plants will have difficulty absorbing the nutrient from the soil.
For example, the availability of phosphorus in soil drops off rapidly as pH drops below 6.0. The availability of boron drops off rapidly as pH rises above 7.5. Most elements have high availability when soil pH is between 6.0 and 7.0 (slightly acidic), and most plants prefer to be in this range.
Of course, there are some exceptions in both directions. Some plants, such as blueberries and azaleas, prefer acidic soils with pH around 4.5 to 5.5. Other plants, such as olives and oats, prefer basic soils. For more information, check out this article from the University of Vermont, which includes information on plants and preferred pH levels.
When your soil pH is outside of the ideal range for a plant, it will be unable to absorb the nutrients it needs. This leads to symptoms of nutrient deficiency in the plant. Here are some common nutrient deficiencies and symptoms:
- Yellow Leaves – either the whole leaf turns yellow (chlorosis), or just the parts between the veins turns yellow (interveinal chlorosis). For more information, check out my article on yellow leaves and causes.
- Potassium Deficiency – symptoms are reduced growth, weak roots, and small stems. For more information, check out my article on potassium deficiency.
- Iron Deficiency – symptoms are chlorosis, weak growth, and small flowers or lack of fruit. For more information, check out my article on iron deficiency.
- Magnesium Deficiency – symptoms are interveinal chlorosis, necrosis (death of plant tissue), and stunted growth. For more information, check out my article on magnesium deficiency.
- Calcium Deficiency – symptoms are necrosis, stunted growth, poor production, and blossom end rot in tomatoes and peppers. For more information, check out my article on calcium deficiency.
- Nitrogen Deficiency – symptoms are chlorosis and poor growth. For more information, check out my article on nitrogen deficiency.
Of course, it is difficult to tell whether a nutrient deficiency in your plants is caused by low levels of nutrients in the soil or a pH imbalance. For that reason, I recommend getting a soil test to determine soil pH.
Getting A Soil Test To Determine pH
A soil test will tell you for certain the levels of pH and various nutrients in your soil. You can buy soil test kits online or at a garden center and perform the tests yourself.
You can also send away a soil sample to your local agricultural extension. They will test the soil more precisely in a lab, and they will give you more information than a do-it-yourself soil test kit. If you tell them what you are trying to grow, they will also send detailed recommendations on how to treat your soil.
It is always a good idea to get a soil test before treating your soil with any additives to modify pH or nutrient levels. That way, you can be certain that you are using the right solution for the right problem.
Correcting Soil pH With Additives
If your soil test results confirm that pH levels are outside of an acceptable range, then you can amend the soil to make the necessary changes.
Raising Soil pH
If your soil pH is to low (acidic), you can raise the pH by adding lime (calcium carbonate) or dolomitic lime (calcium magnesium carbonate). For more information, check out my article on how to raise soil pH.
Remember that too much calcium in your soil can prevent a plant from absorbing magnesium, since these two elements “compete” for uptake by a plant’s roots. If your soil test reveals high calcium or low magnesium levels, use dolomitic lime instead of ordinary lime to raise your soil pH.
Finally, remember that if you need to raise your soil pH by quite a bit, you should add lime gradually so you don’t shock your plants with a rapid change in soil pH.
Lowering Soil pH
If your soil pH is too high (basic), you can lower the pH by adding sulfur. For more information, check out my article on how to lower soil pH.
Remember that the amount of sulfur you need to add may vary with the type of soil. Also remember that it may make sense to add sulfur a little at a time, instead of all at once. This will help to prevent a “pH shock” to your plants, by keeping the soil pH from changing too quickly.
What Are The Causes of Acidic Soil (Low pH)?
Now we know how to treat acidic soil, but what causes it in the first place? For one thing, using nitrogen or sulfur fertilizers, such as ammonium nitrate, will cause soil to become more acidic over time.
Also, areas that are rainy and humid tend to have more acidic soil. This is due to leaching of nutrients such as calcium, magnesium, and potassium from the soil.
In addition, the decay of organic matter can lower pH over time. If you add unfinished compost or manure to your soil, the decaying organic matter can make the soil more acidic.
Finally, the plants themselves can make soil more acidic by pulling certain nutrients out of the soil as they grow.
What Are The Causes of Basic Soil (High pH)?
Having too much of an alkaline element in your soil, such as calcium or magnesium, can cause a high soil pH. This could occur if you used too much Epsom salt (magnesium sulfate) or lime (calcium carbonate) to supplement magnesium or calcium for your plants. It could also occur in soils that naturally have high levels of calcium, such as limestone soils.
How Can You Stabilize Soil pH?
Once you get your soil pH to the right level, you will want to maintain it so that you don’t have to constantly treat your garden with sulfur or lime.
There are a couple of ways to stabilize your soil pH so that it changes less rapidly: adding organic material and improving soil drainage. For more information, check out my article on how to keep pH stable in soil.
Add Organic Material
If your soil is sandy, its pH will change more rapidly than clay or other soils. To remedy this, add compost to your soil. In addition to providing organic material and nutrients to your garden, it will act as a pH buffer, preventing rapid changes in pH.
For more information, check out my article on how to make compost.
Improve Soil Drainage
If your soil is clay, it is likely to retain water and drain poorly. If you have not added organic material, do so to improve the drainage of your soil.
You should also consider digging trenches, laying pipes, or installing rain barrels to divert water away from wet areas of your garden. Once you improve the drainage of your garden, you can prevent leaching (washing away) of minerals, which will prevent changes in soil pH.
For more information, check out my article on how to improve soil drainage.
By now, you have a good idea of what a pH imbalance can do to your plants, along with ways you can solve the problem.
I hope you found this article helpful – if so, please share it with someone else who can use the information. If you have any questions or advice of your own about soil pH, please leave a comment below.