pH Explained

In my early years of gardening I didn’t know the difference between pH and PMS; I had no idea if my soil was alkaline or acidic. Fortunately most things I planted grew anyway, but I did have trouble with a few plants, and I now suspect that the soil’s pH was the problem.

Soil SamplepH stands for “parts hydrogen” and the pH scale measures how acid or alkaline the soil is. The scale ranges from 0 to 14; anything below the neutral point of 7 is acidic, and anything above 7 is alkaline. Most gardens have soils that range between 4.5 and 7.5.

In general, most areas of the United States receive regular rainfall, and these regular rains keep soils on the acid side. But locations where rainfall is less prevalent usually have neutral or alkaline soils. Local conditions such as the composition of the bedrock, or the vegetation present may also affect the pH.

Now this is all very interesting, but what does it have to do with our gardens? Well, pH is of concern because it influences how available nutrients are to the plants. For example, phosphorus, calcium, potassium, and magnesium are most available to plants when the soil is in the neutral range. And if the soil is very acidic, the bacteria that make nitrogen available to plants are not as active, so less nitrogen is there for the plants’ use. In extremely alkaline soil, phosphorus, iron and trace elements are unavailable for plant uptake.

So if the pH of the soil is off, there may be adequate nutrients in your soil, or you may be fertilizing, but your plants can’t absorb what is there.

The majority of garden plants (especially annuals, perennials, and most vegetables) grow best in soil that is near neutral, from 6.5 to 7.0. Other plants (azaleas and blueberries for example) need acidic soils, and some, such as delphiniums, prefer soil which is more alkaline.

If the pH of your soil is wrong for the plants you are growing, there are things you can do to change it. The addition of lime or wood-ashes will bring the pH of acid soils up closer to neutral, and digging sulfur or peat moss into the garden will bring the pH down if it is too high.

But don’t treat your soil with anything before you know what the pH is. What has been put on or in your soil in the past may be affecting the pH today. Even the water that is sprinkled on your lawns and flowerbeds might be changing the pH, so is important that gardeners not assume that their soil is either acidic or alkaline. Put a small trowel full of dirt into a baggie, and have it tested by a lab or your local Cooperative Extension, and be sure to mention what you have growing in the soil that is being analyzed. They will tell you what the pH of that soil is, and if you need to alter it to suit what is growing in that area.

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