How To Lower pH In Soil Fast: what to add

In chemistry, pH is a scale used to specify how acidic or alkaline a substance is. Acidic solutions have a lower pH, while alkaline – or basic – solutions have a higher pH. If the pH level is exactly 7, such as that of pure water, it’s neutral.

Different types of plants need different levels of soil pH to survive and thrive. And though Soil pH varies from region to region and one garden to the next. Most plants need a pH between 6.5 and 7, but others – flowers like azalea, marigolds or heather and fruits and vegetables such as blueberries, potatoes, peppers – need acidic conditions.

Once you’ve decided what to plant, it’s best to verify the soil’s current pH level before making any adjustments.

How to lower pH in soil

In order to correct alkaline soil, you will typically need to introduce a source of acid. You can also add compost, manure or organic soil amendments like alfalfa meal to increase the nitrogen level of the soil which will gradually decrease the pH by approximately half a point.

Organic gardeners commonly use elemental sulfur to decrease the pH level of their soil; however, sulfur requires some time for the soil bacteria to convert it to sulfuric acid.

The speed of the conversion is dependent on the particle size of the sulfur, the temperature and the degree of moisture of the soil and the amount of bacteria present. Sulfur will only work during the warmest months of summer when bacterial activity peaks.

It can therefore take up to several months for this method to decrease the soil pH value.

Elemental sulfur is the best choice for lowering the pH of highly-dense soil with a heavy clay component; adding organic materials to that type of soil will only cause it to retain more moisture, which will make it more alkaline. 

As it takes so long to act, element sulfur is best introduced at the end of the last planting season.

How to lower pH in soil fast

What is the fastest way to lower pH in soil? – While there are methods that will make the soil more acidic very quickly, their results may vary, and in some cases, they may over-correct the soil pH and do more harm than good to the garden.


While it’s a well-known myth that coffee grounds are a quick fix for lowering soil pH, in fact most of the organic acids in coffee are water-soluble, and flush out into the brew. Used coffee grounds have a pH around 6.8, which is so close to neutral that they won’t lower pH much; however, they do add a little nitrogen, so they can help reduce pH over time, just like manure or compost.

Freshly ground or brewed coffee has an average pH of about 4.5, depending on the region in which it was grown. So if you need to drop soil pH more quickly, try spreading fresh grounds throughout the soil or watering your plants with leftover (cold) coffee that is diluted 50-50 with water. This method works especially well for smaller volumes of soil such as for houseplants or container vegetables.

How to lower pH in soil with vinegar

Vinegar is a kitchen staple, because it has a wide variety of uses; it can be used as a condiment, to add flavor to cooked dishes, and even to clean sinks and counters when the cooking is done. This potent liquid is also useful to gardeners, and it can be used to naturally adjust the pH level of soil without the need for harsh, commercially manufactured products.

Vinegar is a diluted, liquid form of acetic acid, and depending on what the vinegar is made from and how it’s processed, it may also contain other things, like vitamins. The average pH of commercially manufactured white vinegar, like that sold in supermarkets, is 2.4, making it highly acidic. Organic gardeners can find an organically-made vinegar.

Vinegar can be sprayed onto the soil or introduced through an irrigation system. A cup of vinegar mixed into a gallon of water is ideal for plants like azaleas and rhododendrons.

Aluminum sulfate

One of the quickest-acting acidic soil additives is aluminum sulfate; it produces acidity in the soil as soon as it dissolves, which is basically instantly. If you need to urgently lower the pH level of your soil, aluminum sulfate is a great choice.

Keep in mind that using too much additive can be harmful for your plants, so it’s best to verify the usage details based on the starting pH of your soil. Aluminum sulfate shouldn’t be used for large applications because it can lead to aluminum accumulation or even aluminum toxicity in the soil.

Sulfur-coated urea

A common ingredient in many slow-release commercial fertilizers, sulfur-coated urea is a fairly quick-acting soil additive. It can lower the pH level of the soil considerably over time, yet will produce some effect within a week or two of being introduced.

If you were already planning to fertilize the soil as well as decreasing its pH, simply choose a fertilizer that contains urea; the sulfur-coated urea content does vary from one brand of fertilizer to another, so remember to consult the mixing instructions to determine the proper amount to use.

Iron sulfate

A good choice for heavily compacted soil with a high clay content, iron sulfate relies on a chemical reaction to create acidity in the planting beds, making it less dependent on temperature conditions than elemental sulfur.

Iron sulfates also act faster than elemental sulfur and can significantly reduce pH in as little as three or four weeks; therefore, it can be used during the same season you decide to plant acid-loving plants.

It may take more than 10 pounds of iron sulfate per 100 square feet of soil to reduce the pH level by one; if you do need to add more than that, it’s best to split the quantity into two applications that are spaced a month or two apart. This will give the soil enough time to absorb the iron sulfate between applications.

Iron sulfates can leave rusty stains on clothes, so it’s best to wash any clothes that have come into contact with them separately to avoid damaging other items; they can also stain cement surfaces such as patios or sidewalks.

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