How to Raise the pH of Soil

Reviewed by Amanda Rose Newton

Regardless of what you planted in your yard, the pH of the soil is a crucial parameter for plant growth because the availability of nutrients to plants hinges upon it. Most edibles, grasses, and most ornamentals do best in neutral to slightly acidic soils (pH 5.8 to 6.5) whereas acid-loving azaleas, rhododendrons, blueberries, and conifers thrive in acid soils (pH 5.0 to 5.5). A few edibles, including cruciferous vegetables, and perennials such as columbines, can thrive in slightly alkaline soil (pH 7.0 to 8.0).

The soil in the eastern and southeastern United States and in the Pacific Northwest is moderately acidic. In the western United States (with the exception of the Pacific Northwest), the soil is alkaline due to the alkaline parent materials that developed into soil over thousands of years. The soil in the Midwest and the Great Lake areas tends to be in the neutral pH range. Sandy soils, which you find along coastlines and in Florida, tend to run alkaline.

However, soil acidity is not static. Soil can become more acidic for natural or manmade reasons, including excessive rainfall, breaking down of organic matter, and high-nitrogen synthetic fertilizers. If soil the acidity hits a level where plant growth is affected (below a pH of 5.0), it’s time to take action and increase the soil pH.

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Test the pH of Your Soil

The very first thing, and an absolute must, is a soil test to check the pH. If you don’t think you need a full-scale soil test through your local Extension Office, you can also do a slimmed down version and buy a do-it-yourself pH test kit from a nursery or garden center. If you test the soil frequently, it might be a good idea to purchase a pH meter.

If it turns out that you need to increase the pH of your soil, keep in mind that depending on the amendment you are adding to the soil, it takes time for the soil pH to change. That’s why it is best to do a pH soil test in the fall and then amend the soil in the fall or winter so it’s ready for next year’s planting.

Never alter the soil pH without doing a soil test before, it can harm your plants.

Methods to Raise Soil pH

With the result of your pH test in hand, determine if the soil pH is indeed too low for the type of plants you want to grow. If the pH is within range, do nothing.

Otherwise, here are the two soil amendments you can use to increase the soil pH before planting:

Limestone

What is sold as garden lime or limestone is calcitic lime, the most commonly used material to make soils less acidic, It is ground limestone and available in pulverized, granular, pelletized, and hydrated form. The finer the particles, the faster the lime changes the pH of the soil so pulverized lime works the fastest but it also has the drawback of clogging, which occurs less with granular and pelletized lime. Hydrated lime raises the pH quickly and can be applied any time during the growing season but it needs to be handled with extra care, as it is highly reactive and contact can cause irritation to eyes, skin, respiratory system, and the gastrointestinal tract.

Lime needs to be worked into the soil thoroughly and it needs water to react. As for the amount, it depends on the current and the target pH of the soil, as well as the texture of the soil. Soils that are high in organic matter and low in clay require less lime than heavy clay soils to obtain the same pH increase.

Dolomitic Lime

Unlike calicitic lime, which contains only calcium, dolomitic lime also contains much higher levels of magnesium, a micronutrient. In their ability to neutralize soil acidity, however, the two materials don’t differ. Dolomitic lime is usually sold in pelletized form.

Raising the Soil pH After Planting

For a vegetable garden, the soil should be amended in the fall or winter before planting in the spring. For established plants, on the other hand, for example when you want to increase the soil pH in order to turn blue hydrangeas pink, you can add dolomitic lime in the early spring, as well as in the late spring and fall. The same applies to using lime for lawn. Unless you live in an area with wet summers, adding lime during the summer is not a good idea, as it needs water to react, and it takes time for the soil pH to change.

Factors Affecting the pH of Soil

The type of rocks in an area plays a role whether the soil tends to be acidic or alkaline. Acidic granite rock contributes to acidic soil whereas alkaline shale or limestone contributes to alkaline soil.

Frequent and heavy rainfall leaches away the alkaline elements of the soil and makes it more acidic over time. In arid areas with little precipitation, those alkaline elements remain in the soil, therefore it is more alkaline.

Another factor affecting the soil pH are accumulated leaves and pine needles from lots of deciduous trees, and other decaying organic matter, which can also make soil more acidic.

Frequently Asked Questions

Will baking soda raise soil pH?

Baking is often touted as an easy, low-cost, and fast way to increase the soil pH, but it is a salt (sodium bicarbonate) that was not formulated for agricultural use. Sure, upon contact with water it makes a solution alkaline and neutralizes acidity but that is nothing but a quick fix that risks burning plants.

Which trees prefer high pH?

There are several trees that are tolerant of alkaline soil or prefer it, including redbud and linden trees.

What if I don’t raise the pH of the soil?

Depending on how low the pH is, it might affect plant health. But unless the soil is extremely acidic, you might just be fine. Or, you can adjust and grow plants that prefer acidic soil.