Gardening is a fulfilling, enjoyable, and even meditative experience that makes hobbyists and enthusiasts around the world feel more connected to their landscapes. However, for a practice that feels wholly intuitive and based in the natural world, you’d be surprised to find out the crucial role that certain scientific concepts, like pH, play when it comes to its success.
Here are 5 reasons why soil pH is so important:
- Soil pH affects how many nutrients reach your plant.
- Different plants prefer different pH levels.
- pH allows garden plants to reach nitrogen sources.
- Nutrient deficiencies can be a direct result of pH imbalance.
- pH can affect the population of soil microbes.
In the following sections, I’ll dive into what soil pH is and the reasons why it can be so essential to your garden. I’ll also provide you with some ideas on how to test your soil pH and the best ways to fix it in the instances when it’s off.
1. Soil pH Affects How Many Nutrients Reach Your Plant
Soil pH affects the availability of nutrients within your soil, and as we know, plants need nutrients to grow and thrive.
Your plants may need some combination of the following essential 17 nutrients:
- Carbon
- Phosphorus
- Magnesium
- Boron
- Potassium
- Manganese
- Chlorine
- Copper
- Molybdenum
- Calcium
- Hydrogen
- Sulfur
- Calcium
- Oxygen
- Nitrogen
- Iron
- Nickel
Compounds like hydrogen, carbon, and oxygen are naturally received by plants through the air. However, the other 14 nutrients typically come from the soil we use in our gardens. Rich, nutritious soil is so important, as it’s the plant-world equivalent to a well-balanced diet.
Some plants do prefer more acidic soil while others thrive better in more alkaline soils. Regardless, the pH determines the amount of nutrients in the soil your plant roots can access. Even if your mixture is rich in nitrogen, but the pH is strongly acidic, your plants won’t be able to get to it.
Factors that Affect Soil Acidity
Soil pH sounds like a scientific term and may remind us of rainbow-colored testing strips in high school science class. However, gardening is connected to science more than you’d think, even if we don’t have to wear a lab coat and goggles.
Something to remember when talking about soil pH is the pH scale. A pH of 7.0 is neutral. Anything below 7 indicates an acidic environment, and anything higher than 7 indicates alkaline soil.
Generally speaking, your soil pH needs to be between 6.0 and 7.0 for most common gardens, with 6.5 being ideal for crop production, but what does that mean?
Soil Composition
Soil pH is the measure of acidity in your soil. Basically, substances can either be acidic, alkaline, or somewhere in between. The proportion of acidic and alkaline substances in your garden soil can determine the soil’s overall pH.
Region and Amount of Rainfall
It also helps to be familiar with the inherent soil pH in your region when planning which crops to grow in your field or plants to grow in your garden. For instance, areas with plenty of rainfall, such as in the eastern and southeastern parts of the US, have more acidic soil.
In contrast, most regions in the western and southwestern parts of the US have more alkaline soil due to the minerals present in the soil and the insufficient amount of rainfall to leach these alkaline minerals from the ground.
Landscape and Crop History
Although these are considered the common regional pH conditions of the soil, it’s still crucial to check your garden’s soil pH. Various factors, such as landscape design and crop history can affect your specific area’s soil acidity.
For instance, if you live in an area with slopes that receive adequate rainfall, the soil pH can be lower even if the regional soil pH is on the alkaline side. Such is the case in some elevated areas in Colorado although most agricultural lands have pH levels ranging from 7.0 and 8.2.
Crop history also plays an important role because plants that consume alkaline minerals can eventually leave behind more acidic soil once they’re pulled out.
That’s why determining your soil’s acidity is necessary for a thriving garden. The pH level of your garden determines what nutrients will be present. A slight acidity is good for some plants, while other plants need more alkaline soil.
This video helps to explain what this looks like in your garden:
Though Brian and Darren from AgPhD talk about soil pH in the context of farming, the same principles remain true in even the smallest of gardens. You need to know your soil’s pH level if you want to continue nurturing your garden, and it may give you some insight into why you might be having problems.
2. Different Plants Prefer Different pH Levels
As discussed, various plants prefer different pH levels. Even if you understand that pH makes nutrients available for your plants and you follow the 6.5 rule, you may be stumped to find that some of your plants aren’t taking to your soil.
Here are some examples of plants that thrive in highly acidic soils with pH levels between 4.5 and 5.5:
- azaleas
- rhododendrons
- blueberries
- conifers
On the other hand, ornamentals like roses and most vegetables prefer an almost neutral environment with pH levels ranging from 6.5 to 7.0.
If your soil is more alkaline, you’re better set to plant quite a few vegetables and ornamentals. However, it’s vital to keep an eye on the soil’s alkalinity because nutrients like iron can become deficient in highly alkaline soil.
You can successfully grow the following plants in slightly alkaline soil because they can tolerate pH levels slightly above 7.0:
- Beets
- Brussel sprouts
- Cauliflower
- Garlic
- Kale
- Pea
- Pumpkin
- Spinach
- Tomato
On the other hand, if you’re more interested in ornamental plants but have alkaline soil, you’ll have higher chances of success growing columbines, lavenders, and hostas.
Having said that, these plants won’t successfully thrive at a pH level much higher than 7.5
3. pH Allows Garden Plants to Reach Nitrogen Sources
Levels between 6.2 and 6.8 seem to be the sweet spot for most gardens. But why is this?
Grow Appalachia uses a great metaphor in this video, where they explain that reaching nutrients in the soil is kind of like reaching for food in the middle of a giant table:
Basically, without a monitored pH, your plants won’t be able to gather all of the available nutrients. Nutrients are present and obtainable by plants at specific pH values. Most of the compounds are available at somewhere between 6.0-7.0 pH, with 6.5 being the go-to for most gardeners.
Therefore, even if your garden is nitrogen-rich but the pH is very low, your plants won’t be able to tap into these nitrogen sources and will become nutrient deficient.
I discussed more deeply about nutrient availability and deficiencies in acidic soil in my other article: Does Acidic Soil Contain More Plant Nutrients?
4. Nutrient Deficiencies Can Be a Direct Result of pH Imbalance
Nutrient deficiencies are a gardener’s worst nightmare. Unlike watering or sunlight, where you can just water less or add a sunshade, there’s little a gardener can do quickly to fix a nutrient deficiency. Additionally, there are 17 essential nutrients for plant growth, and figuring out which one your plant is lacking can feel like finding a needle in a haystack.
Deficiencies can directly result from soil pH, especially if you’ve already tried feeding your soil everything it needs, but it seems as though it’s just not getting it. Finding soil rich in nitrogen or phosphorus is a great way to help with plant nutrient deficiencies, but not if the soil pH isn’t right in the first place.
If you’re sure that your soil is rich in nutrients, you may want to scan it to determine its pH level. Plants with nutrient deficiencies may rot, lose color, change colors, wilt, or display any number of other symptoms.
While these may just result from nutrient-absent soil, they can also be a sign that your soil pH is off and plants cannot get the nutrients they need.
5. pH Can Affect the Population of Soil Microbes
The soil pH value can also affect the population of microorganisms within the soil.
This is one of the lesser-known consequences of having an off-balanced pH, but there’s tons of research backing it up. As most gardeners already know, soil microbes come in one of two categories: beneficial or harmful to your plants.
Beneficial microbes help break down soil nutrients and organic matter into forms that are readily absorbable for the plant roots.
On the other hand, harmful fungi, such as Fusarium, Pythium, and Phytophthora can cause root rot when in high enough populations. In addition to soil pH, they’re also highly dependent on soil moisture.
Some bacteria can only grow and thrive within a specific pH range, while others are resilient. Regardless, your pH level may affect how much bacteria is growing within your garden. If you’re facing bacteria issues, this may be an indicator that adjusting the soil’s pH level might fix them.
Research showed that certain co-existing soil bacteria and fungi populations peaked when pH levels were at 5.5 for acidic soil and 8.3 for alkaline soil. Beyond these levels can be detrimental for both microbes and your plants (except for acid-loving plants).
How to Test the pH of Garden Soil
Hopefully, by this point, you’re convinced of the importance of soil pH. pH determines the nutrients available to your plants, can affect microbial populations, and influence whether your plants can grow and thrive.
However, unlike a waterlogged garden or a patch of soil dehydrated from the sun, figuring out what your soil pH is will take more than just a look.
To test your soil’s pH, you can use test kits, a meter, or send a sample to a lab. Each is a viable approach, but the best solution for you will depend on your budget and the size of your garden. Testing your soil pH will give you some insight into the acidity or alkalinity of your garden.
Each of these methods will tell you your soil pH, but only a few will give you information regarding what nutrients are missing in your soil, as well. For the purposes of soil pH testing alone, your budget is what should have the heaviest influence on this decision.
I’ll expand on the three methods below:
Meter
A pH meter reads the acidity level of your soil and then displays it. The benefit of pH meters is that you only have to buy one, and they often come with hydration meter and sunlight meter options as well. Another benefit is that these meters can be found in garden supply stores, most chain stores, and on the internet.
However, they won’t be as accurate as a kit, and they won’t tell you what nutrients your garden lacks as a soil sample might.
To use a meter, you have to follow the steps below:
- Pick multiple spots in your garden and loosen the top inch (2.5 cm) of the soil.
- Dig 4-6 inches (10-15 cm) deep and pour distilled water into the hole.
- Wait at least five minutes to let the water seep through and evenly hydrate the area.
- Stick the probe of the device equipment into your garden soil, carefully avoiding any plant roots.
- Record the reading and clean the soil off the probe with a clean towel moistened with distilled water before checking the pH of the other spots.
Kit
A soil pH kit uses a strip of paper or a plastic device to test your soil. Each product comes with its own set of instructions, but you’ll generally add a sample of your soil to the device and add some water or a special liquid to test the acidity.
Soil testing kits can be found at your gardening center and easily found online.
This video gives a visual demonstration of how to use a pH testing kit:
Send a Sample to a Lab
Another option is to send a sample of your soil to a local lab. These results will be the most accurate, as labs use more comprehensive and expensive equipment to test the quality of your soil. They will also be able to test for other components, like nutrients or bacteria, in the same test.
To send your sample to a lab, you usually have to figure out where you’ll want to send your soil first. Each lab will typically provide the bag and instructions for testing your soil samples.
How to Change Soil pH
If you’ve tested your soil pH and found that your soil is leaning to one side of the scale or the other, you may be anxious to fix it. The process can be time-consuming, but there are no quick fixes for your soil pH.
You can fix your soil pH by using various methods, such as adding organic or inorganic substances. You will first need to figure out if your soil is too acidic or alkaline and then decide how you’d like to combat the issue.
Correcting soil pH may be more tedious and less straightforward than solving problems with watering or sunlight, but it’s definitely worth the time. Still, regardless of the method, be sure not to overdo it, as doing so may send your soil to the other end of the spectrum.
Reducing pH
There are numerous ways to reduce the pH of garden soil, but they vary in effectiveness, speed of action, and duration of effects.
Some of the most common methods include the following:
- Adding elemental sulfur
- Using acidic fertilizers like ammonium nitrate or ammonium sulfate
- Pouring a diluted vinegar solution containing one cup (250 ml) of 5% white vinegar in 1 gallon (3.8 L) water
- Amending the soil with sphagnum peat moss
- Adding acidic compost
Increasing pH
Some soils can be too acidic to grow vegetables. Many nutrients become unavailable when the soil pH is below 5.5. Therefore, the only way to make your soil conducive for crops is to raise the pH. Here are some popular methods:
- Adding lime
- Adding wood ash
- Topping the soil with sodium bicarbonate
