At Home in the Range: The Importance of Balanced Soil pH

In the garden as in life — and fairy tales about porridge-eating children — balance is everything.

To keep plants healthy and growing, you have to provide not too much of this and not too little of that. Things have to be (mostly) just right, right down to the soil.

One way to determine how “right” the soil is by measuring its pH level. That tells you how acidic or alkaline the soil is. 

Soil pH is measured on a scale of 0 to 14, with 7 being neutral. Numbers below 7 indicate acidity, while numbers above 7 indicate alkalinity. Most plants are pretty level-headed, preferring a slightly acidic to slightly alkaline range, typically between 6.0 and 7.5 pH. (To know for sure, take a look at the seed packet or the pot your plants came in, or consult an online resource or Master Gardener.)

But why does soil pH matter? 

For one thing, when the soil is the appropriate pH, it’s easier for beneficial microbes to break it down into the essential nutrients plants need to thrive. And it’s easier for the plants to absorb the nutrients, as well.

When the soil is outside the desired range, however — whether it’s too acidic or too alkaline — not only can the nutrients bind to soil particles, reducing nutrient availability, but extreme conditions can damage root hairs. That makes nutrient uptake for the plant about as difficult as sucking a Frosty through a straw.

The results?

• Plants will struggle to grow.
• Leaves will look yellow or brown.
• Stems and roots may weaken, making the plant susceptible to disease.
• Plants will produce fewer flowers or fruit.

How soil goes astray

There are many reasons why soil becomes too acidic or alkaline, some related to natural causes, others to human interaction.

The minerals in the rock that formed the soil are a big influence. Soil formed from granite tends to be acidic while soil formed from limestone is alkaline.

Long periods of heavy rainfall are also a factor. Rainwater leaches out alkaline components and leaves more acidic ones behind.

Garden fertilizers can increase soil acidity if they are high in ammonium. Slow-release fertilizers avoid this problem.

If your tap water is full of salts or minerals, it can alter soil pH, too. Harvesting and using rainwater is a better option; so is getting a water softener.

Poor drainage can make the garden more acidic over time. Adding sand or other coarse materials can help. 

Even composting can have an untoward effect. While composting generally improves soil health, putting too many coffee grounds or pine needles in the bin can lower soil pH. 

Test before you trowel

Before you begin planting, it’s good to know your pH starting point. Test kits or digital meters make it simple to know whether your soil is too acidic, too alkaline, or within an acceptable range. 

Soil pH test kits are widely available and affordable. Most kits include a testing solution, a color chart, and a container for your soil sample.

In general, the test process goes like this:

• Dig up samples from different areas in your garden bed and at depths ranging from 4-6 inches. To improve accuracy, the soil should be slightly moist and not recently fertilized.
• Mix the samples together in a clean container.
• Mix the soil with the testing solution, following the directions on your kit.
• Let the mixture sit for a few minutes. During this time, the solution will change color.
• Compare the color of the solution to the color chart. That will tell you the pH value.

Digital meters are quicker and more precise than test kits. They also need to be calibrated regularly and can be pricey, but their two-step simplicity is a big benefit:

• Insert the meter’s probe into moist soil.
• Read the digital display.

Remember soil pH is not static. You can’t just test once and forget it. Experts recommend testing every three to five years, which allows you to amend the soil as needed.

Change is good

If you don’t have your heart set on a specific plant, you can always choose ones that thrive within your soil’s specific range.

Blueberries, for example, prefer acidic soil (pH 4.5-6.5), as do azaleas, rhododendrons, hydrangeas (for blue flowers), carrots, and potatoes. Alkaline-loving plants (meaning they like their soil pH to be around 7.5-8.5) include lavender, rosemary, yucca, asparagus, and some cacti.  

However, if you have certain plants in mind and your soil doesn’t meet their pH particulars, all is not lost. Amendments can bring things back into line.

To make your soil less acidic, you can use:

• Agricultural limestone, which you can get at your garden center in pulverized, granular, or pelletized form. The finer the grind, the faster it works. Be careful not to overdo it, though. If you raise the pH too much, it can create new problems for your plants.

To make your soil less alkaline, you can use:

• Elemental sulfur, which is also readily available and inexpensive. It works by converting to sulfuric acid in the soil, which is a time-consuming process and requires a fair amount of patience on the gardener’s part.

If you have a variety of plants with different pH preferences, consider growing them together based on their needs. This can help you manage your soil amendments more efficiently.

Here’s to happy plants

Though plants lack our ability to express emotion, they do respond to their environment. Flowers turn their heads to the sun not because they like how it feels but because they orient toward a light source (the scientific term is phototropism). 

When a Venus fly trap shuts its, uh, trap, it’s not feeling angry. It’s simply captured its prey.

And if you’ve ever touched the creeping annual called Mimosa pudica only to have its leaves fold up, that’s not a symptom of shyness. It’s a defense mechanism to keep herbivores from making it a meal. 

Still, gardeners often ascribe emotions to their plants. When we see one flourishing, we say it’s “happy.”

And one reason it’s happy is because it feels at home in the pH range of the garden bed. Its environment is in balance, or “just right.”