How to Lower Soil pH

In chemistry, pH is a measure of the acidity or alkalinity of a substance. The pH scale has a range of 0 to 14; pH near 0 is extremely acidic, pH near 14 is extremely alkaline, and pH 7 is absolutely neutral. In the field of horticulture and horticulture, the pH of the soil in which plants are grown can greatly affect the health and growth of plants. Although most plants tolerate a pH between 6.0-7.5, there are some plants that do best in a narrower pH range, so serious gardeners should learn the basics. for controlling pH. ^{[1] X Research Sources}^{[2] X Research Resources} Read step 1 below to begin learning how to lower soil pH.

Table of Contents

Conduct a pH test

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Test the pH of the soil. Before adding anything to change the pH of your soil, you should always test the soil first to see how far away your goal of lowering the pH is. You can buy a test kit at a gardening center or take a soil sample to your local rural development office to have them try it on.

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Dig 5 small holes in the planting area. The pH in garden soil is fairly easy to determine with a commercially available pH test kit. pH test kits are usually available at home or garden supply stores for relatively cheap prices. To begin testing, you will have to take a soil sample from the site to be tested. Dig 5 small holes (about 15-20 cm deep). Select random locations in the plot; That way, you’ll know the “average” pH of your garden soil. ^{[3] X Research Source} No need to retain the soil excavated from the holes.

Note that the instructions in this section are general only; you should see specific instructions in the pH test kit.

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Take soil samples in each soil cavity. Next, use a shovel or spade to roll up a “slice” of soil on the wall of each hole. This slice will be in the shape of a crescent moon and about 1.5 cm thick. Try to take soil samples of equal size. Place soil samples in a clean, dry bucket.

Take the amount of soil in each soil sample so that a total of 1 liter or more is enough. For most test methods, this amount of soil is sufficient.

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Mix the soil in a bucket and spread it on the newspaper to dry. Let the soil dry until you can no longer see any moisture.

It is important that the soil is completely dry before testing the pH; Humidity can cause inaccurate results. ^{[4] X Research Sources}

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Use the test kit to accurately determine the pH in the soil. Depending on the type of test device, the test method may be different. For many common test kits, you will put a small amount of soil in the test tube, add a few drops of solution, shake well, and let the mixture settle for a few hours. ^{[5] X Research Source} Finally, the color of the solution will change; By comparing the color of the solution with the color on the test kit’s chart, you can determine the pH of the soil.

There are different types of test kits available, so you should read the instructions that come with the test kit. For example, some newer electronic pH testers can determine soil pH almost instantly via a metal probe. You can also collect a sample of soil and bring it to the rural development office for a free soil test.

Use methods to reduce pH

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Add organic matter. Many organic matter such as compost, manure, and acidic mulch (such as pine needles) can gradually lower the pH in the soil. ^{[6] X Research Source} As organic matter decomposes, bacteria and microorganisms multiply and feed on organic matter, creating acidic by-products. Since organic matter takes time to decompose to change the pH of the soil, this option would be great for long-term goals but will not yield significant results in the short term. Many gardeners choose to add organic matter to the soil every year to effectively reduce pH. However, this will not work for heavy clay.

Organic matter can also provide other benefits to the soil; The most obvious is improved soil drainage and aeration. ^{[7] X Research Sources}

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Add aluminum sulfate. To quickly lower the pH, you should not rely on slow-rotting organics. Instead, use one of the many acid-forming additives available at garden supply stores. Of these additives, aluminum sulfate is one of the fastest-acting options. Aluminum sulfate creates acidity in the soil as soon as it dissolves, for gardening purposes this has an immediate effect. ^{[8] X Research Source} Aluminum sulfate is therefore an excellent choice for rapid soil pH reduction.

Depending on the initial pH in the soil, the amount of aluminum sulfate required can vary considerably. Generally speaking, for a plot of land about 30 square feet, you would need to use 0.5 kg of aluminum sulfate to drop 1 degree on the pH scale (for example, from 7 to 6, from 6 to 5). , etc…). ^{[9] X Research Sources} However, using too many additives can be harmful to plants, so you should consult online sources (like here) for more accurate information on how to do this. use.
Do not use aluminum sulfate on a large scale, as this can lead to an accumulation of aluminum and aluminum toxicity in the soil. ^{[10] X Research Source}

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Add sulfur. Another useful additive for lowering soil pH is sublimated sulfur. Compared to aluminum sulfate, sulfur is generally cheaper, more potent (in terms of the amount to be used), and slower to act. This is because sulfur needs to be metabolized by bacteria in the soil to turn into sulfuric acid, and this process takes time. ^{[11] X Research Source} Depending on the moisture content, the number of bacteria present in the soil, and the temperature, it can take up to several months for sulfur to become effective in the soil.

As noted above, compared to aluminum sulfate, you would normally need to use a relatively small amount of pure sublimed sulfur to produce an equivalent pH change. In general, you will need about 90 g of sulfur to reduce 1 pH per 30 m2 of soil. ^{[12] X Research Resources} You can consult online resources (like here) for more precise information on how to use them.

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Add sulfur coated urea. As with sulfur and aluminum sulfate, sulfur-coated urea soil additives can gradually increase soil acidity (decrease pH). As an additive, urea is fairly quick-acting, taking effect within a week or two of being added to the soil. ^{[13] X Research Source} Sulfur-coated urea is a common ingredient in many fertilizers, so if you’re planning to fertilize your plants, you probably don’t have to look for a separate additive. Just choose a fertilizer that contains this type of urea.

The amount of sulfur-coated urea in fertilizers will vary, so you should read the instructions that come with the fertilizer you purchase to determine the right dosage for your garden’s needs.
Sulfur coated urea is a slow-release fertilizer that adds nutrients gradually when plants need it instead of distributing it all at once.

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Add other acidic additives. In addition to the above additives, there are many other substances that can reduce the pH in the soil. Many of these substances are commonly found in fertilizer mixes, while others are sold in their pure form. The time and amount of fertilizer needed can vary widely, so read the information on the packaging or consult with an experienced gardener supply store employee. Additives that can help lower soil pH include: ^{[14] X Research Source}

Diamonium Phosphate
Iron sulfate
Peat
ammonium nitrate

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Grow plants that tolerate alkalinity. If the soil is too alkaline for acid-loving plants, planting alkaline-loving plants can gradually lower the soil’s pH throughout the plant’s life. As plants grow, mature, and die, organic matter returns to the soil to facilitate bacterial growth and gradually help lower soil pH (similar to adding organic matter in the form of organic matter). mulch or fertilizer). Overall, this method is one of the slowest ways to lower soil pH, as plants need to grow before they start adding organic matter to the soil. Some alkali-tolerant plants can be mentioned as: ^{[15] X Research Source}

Some evergreen shrubs (such as boxwood, California lilac)
Some species of deciduous shrubs (such as lilac, orange jasmine, kumquat)
Some species of perennial plants (such as pick, set of pleasures)

Identify low pH soil-loving plants

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Lower soil pH for shrubs like azaleas. Some flowering shrubs such as rhododendrons need to grow in relatively acidic soil. These plants are usually native to areas with a lot of rain, such as the Pacific Northwest of the United States (heavy rain lowers the pH of the soil). ^{[16] X Research Source} With these shrubs, a pH of 4.5 – 5.5 is optimal, a pH up to 6 is also acceptable. ^{[17] X Research Source}

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Lower the pH for flowers like begonias and hydrangeas. Many brightly colored flowers, such as petunias and begonias, do best in acidic soil. For some of these flowers, changing the acidity from mild to very high can produce a marked change in the color of the flower. For example, hydrangeas when grown in soil with a pH of about 6.0 – 6.2 will produce pink flowers, and when the pH is reduced to about 5.2 – 5.5, the plant will produce purple flowers. /blue. ^{[18] X Research Sources}

The blue color of hydrangeas grown on low pH soil is due to the chemical aluminum in the soil. When the pH of the soil is low, hydrangeas are more likely to absorb aluminum in the soil, and this phenomenon manifests itself in the color of the petals. ^{[19] X Research Source}

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Lowers soil pH for evergreen plants. Many species of evergreen conifers grow on slightly acidic soils. For example, spruce, fir and pine all grow well in soil with a pH around 5.5 – 6.0. In addition, the leaves of these plants can add neutral or alkaline organic matter, helping to lower the pH in the soil when the leaves rot.

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Lowers soil pH for some berry species. Perhaps the most typical acid-loving plant is the blueberry. They grow well in highly acidic soil (pH 4 – 5 is ideal). However, there are many other berry species that also prefer acidic soils. For example, cranberries grow best with a pH of 4.2 – 5.0, while gooseberries, Greek grapes and elderberries typically thrive in soil with a pH around 5.5. – 6.5. ^{[20] X Research Sources}

Advice

Some soil amendment chemicals come in spray form.
It is important not to overuse soil-modifying chemicals of any kind, as these chemicals can have long-term adverse effects on the soil and the environment.
Plants that live in soil with an inappropriate pH will not grow well, because some nutrients will bind in the soil making it impossible for plants to absorb.
The effects of elemental sulfur will last for many seasons.
Elemental sulfur will usually be most effective when used during the spring months, and is very difficult to use once the plants are planted.
Soil pH affects everything from drainage to soil erosion.
Use natural compost whenever possible. This will benefit the plant by adding nutrients. Composting is a great way to utilize grass clippings and kitchen waste.
Elemental sulfur and compost facilitate biological reactions, while aluminum sulfate and ferrous sulfate create chemical reactions.

Warning

Excessive use of aluminum sulfate can cause soil toxicity.
If you accidentally spill urea, aluminum sulfate or sulfur on the leaves, you need to rinse the leaves with plenty of clean water. Chemicals deposited on leaves can “burn” the leaves and harm the plant.

Steps

Conduct a pH test

Use methods to reduce pH

Identify low pH soil-loving plants

Advice

Warning

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