Last Updated on December 23, 2021 by Grow with Bovees
Knowing the difference between acid and alkaline soil will help you to much better understand which plants you can grow the best.
Most plants do well in soil which is neutral or slightly acidic, but there are some which require distinctly acidic soils.
They will not grow in soil which is even slightly alkaline, and they should, therefore, not be planted in regions where the soil and water is alkaline if you wish to grow healthy plants.
The acidity or alkalinity of the soil is measured in what is known as pH values.
In this article we will go through what to do and what not to do when wanting to make your soil acidic.
What Does pH Mean?
A pH scale ranges from 1 to 14 and these numbers are used to express the degree of acidity or alkalinity. A pH of 7 on the pH scale shows that the soil is neutral – it is neither acid nor alkaline.
The change up or down of more than 1 is important as a change of a single digit indicates a tenfold increase in acidity or alkalinity.
Soil with a pH of 5 is ten times more acidic than one with a reaction of 6.
Most plants grow well in soil with a reaction between pH 6 and 6.5, but plants which like an acidic pH level in soil may require a pH of 5 or even lower, while the lime-loving one’s may need a pH of 8.
Acid soils tend to occur in regions of high rainfall and alkaline soil in areas where the rainfall is low, but this is, of course, not universally true.
How Can I Test the pH of My Soil at Home?
There are many risks involved with growing your own food, including exposure to pesticides and chemicals, diseases, and environmental threats like flooding, which can destroy your crops overnight.
One of the best ways to mitigate these risks is by testing the pH of your soil on a regular basis.
And there’s no better way to do this than with a simple pH meter. Correct levels are important for plant health.
There are soil pH test kits available for doing soil tests oneself or one can send soil samples to a professional lab who does tests of this kind. Doing this will provide you with the most accurate and precise pH level result.
Home Soil Test Kit
If you are not too worried about achieving accurate results, obtaining a home soil testing kit and using it by following its instructions to perform a basic soil test, will suffice.
With most testing kits, you would have to take a small soil sample and mix it with a chemical and water in order to obtain the pH value. A lot of the kits will also measure the amounts of potassium, phosphorus and nitrogen present in the soil sample that is being tested.
Another way of testing your soil pH level — this method is probably the most convenient and also the most accurate, providing you with an exact measurement — is to send a decent-sized sample to your local county extension office and have the soil professionally tested in the lab.
With lab testing, you will most likely also get a soil fertility analysis, which can provide you with more information on what type of fertilizer is needed, if any at all.
A third method to test your soil’s acidity, is to purchase a digital soil meter. Using these, is the quickest testing method.
These meters are easy to use. Simply place the probe about 4-6 inches deep into the soil which needs testing. The result will appear on the meter automatically. Digital meters are great for use in container gardens and potted plants.
Be aware that the accuracy of results varies a lot in digital meters, and they are only able to measure pH, light and moisture — not fertility.
Types Of Soil
Now that you have figured out what the pH level of your soil is, you can start thinking of how to lower it if the result is alkaline. But before adding anything to your soil to make it more acidic, it is important to figure out which soil type you are dealing with.
Making any sort of chemical changes to your garden soil without knowing its type, may affect the outcome of the plants growing in your garden.
The best and easiest way to find out which soil type you are dealing with in your garden, is to simply pick it up with your hands and feel it. Be aware of what the texture is like. If it is moist and loose, it is most probably slightly more acidic rather than basic, which makes it easier to continue the process of amending your soil.
If, however, the soil feels clumpy in your hands, forming little lumps, the soil is most likely made of clay, which is extremely alkaline, making the process of acidifying your soil a bit more difficult.
In such an event, to find heavy clay soil in your garden, you would need to add another substrate to it which will aid in making it more acidic. Spreading elemental sulfur across the clay like soil can assist in lowering the pH significantly.
Amending clay like soil is a long process, and it should be done a minimum of 12 months before you wish to begin planting your shrubs in it.
Can I Change The pH of My Soil?
Where the soil is too acidic for good growth, a sprinkling of lime should be applied to the soil at the time of planting. But lime should not be used unless the pH is lower than 6, and the plant requires a more alkaline soil.
Lime tends to make food elements in acid soil more readily available, but, in soil which is highly alkaline with a pH of 8 or higher, the opposite happens and plants will die because the necessary food elements become unavailable.
In regions where the soil is alkaline, it is advisable to choose plants which are tolerant of such soil.
The alkalinity of the soil can be reduced by the regular application of certain chemicals, but it is nevertheless wiser to select plants that tolerate alkaline conditions rather than to have to treat the soil constantly.
Iron sulfate, aluminum sulfate and iron chelates, obtainable from garden stores, are quick-acting in changing the character of the soil.
How often it is necessary to apply this kind of correction depends on the nature of the water used in the garden. If it is highly alkaline, the salts will build up in the soil fairly quickly.
Plants which like acid soil (e.g. azaleas) should never be given ordinary garden fertilizers as these have an alkaline reaction and can cause their demise.
Even compost to which lime has been added may have an adverse effect on them.
Such plants show chlorosis, i.e. yellowing of the leaves when the pH value of the soil is too high, and the ground should be treated around the base of the plant with one of the chemicals mentioned above. A mulch of pine needles or oak-leaf compost will also help to acidify the soil.
Sphagnum Peat Moss Makes Soil Acidic
Peat moss is a popular thing to use as a gardener to lower the soil’s pH. Peat moss has a pH which commonly ranges between 3 and 4.5 on the pH scale, making it quite effective when used to acidify soil.
Another benefit of using peat moss is the organic material that it adds to your garden soil when using it.
Amending the pH of your soil can be done in two different ways;
Add it to the soil before planting shrubs that are fond of acidic soil. Acid loving plants include Azaleas, Rhododendrons, Hydrangeas (if you want blue flowers), Camellias, Gardenias and Magnolias.
If you choose to use this method, start by spreading out a layer of peat moss which measures around 2-3 inches across the area in which you want to plant your shrubs.
Continue by working it so that it mixes well with the soil. Working it until it reaches a soil depth of about 8-12 inches deep. As a rule of thumb, make sure that the moss is worked into the soil as deep as you plant roots are long.
This is the more effective method to use as it acidifies the soil almost immediately after working the moss into the soil. It also instantly creates an acidic environment around your plants root system, which is where you need the lowered pH to be.
You can also go about adding your sphagnum peat moss to an already existing plants.
This can be done by mulching a 1-2 inch layer of moss around the soil to acidify it. Mix the moss through the top few inches of your garden bed soil, taking care not to disturb the plant’s roots.
This method is also an effective one. It will, however, take more time for the peat moss to seep through the soil and acidify the areas where the roots of the plants are located.
Naturally Acidifying Soil — The Vinegar Solution
There are plenty of chemical substances that can be used to lower the pH of your soil. Most of these products, however, take time to achieve the desired result. Using a substance such as elemental sulfur can take up to a year to reach low pH levels in soil. This means a lot of planning to prepare your garden for the growing season.
A common way to acidify your soil fast and naturally, is by making use of vinegar. Certain types of vinegar also carry with it the benefit of adding nutrients to your soil as some contain vitamins and other nutrients.
Vinegar is also easy to find. Simply get it when doing your weekly grocery shopping. It is cheap and there are no restrictions as to which one you choose to use for your soil.
White vinegar is a highly acidic liquid, with an average pH value of 2.4 and there are several ways in which you can use it to make the soil in your garden more acidic.
One way is to dilute the vinegar with some water. Fill a cup with any type of white vinegar and mix it into a gallon of water, then simply pour the mixture over the soil which you want to prepare for planting using a watering can.
If you have an irrigation system in place in your garden, simply insert the vinegar mixture into the irrigation lines and let the system do the work for you. With this method, you will achieve a more even distribution for your garden soil and plants.
Adding vinegar to the soil also has other benefits, apart from acidifying soil. Turns out that, due to its acidity, vinegar is quite an effective weed killer and many species of bugs and insects are repelled by the smell of the vinegar, aiding in bug problems or insect infestations.
Organic Matter & Well-Decomposed Compost
Compost — this can be homemade compost or even compost liquid. Certain mulches and compost manure are the types of organic matter that can be added to soil in order to lower its pH. Making use of this method is, however, not a quick solution.
Organic matter works in such a way that the decomposition process releases byproducts that are acidic. These byproducts are slowly released into the soil and, overtime, it will lower its pH. This is quite a long process. You can expect it to take effect after a couple of seasons only.
Sulfur To Raise Soil Acidity
Using sublimed sulfur is probably the most cost-effective method to choose. It is also a very safe way to reduce the pH of your soil. It is, however, one of the slower processes.
Before the sulfur can start to lower the soil pH, it needs to be turned into sulfuric acid. This is done by bacteria found in the soil, and it can take 3-4 weeks and up to a few months to significantly affect the pH.
In order to protect your plants, the recommended amount of sulfur that should be used is 2 pounds of sulfur for every 100 square feet.
Aluminum Sulfate & Ferric Sulfate/Iron Sulfate
Using aluminum or iron sulfate is a quick method to reduce your soil’s pH when preparing it for the planting season. As soon as they start dissolving in your soil, the pH will start lowering at a fast pace. You will unfortunately need large amounts of it to do the job, which could affect your plants badly if you are not careful.
Be sure not to exceed using an amount of 5 pounds of iron sulfate or aluminum sulfate for every 100 square feet.
Do Used Coffee Grounds Raise or Lower Soil PH?
No. Used coffee grounds are fairly neutral.
The acidity of the coffee grinds is tied up in the coffee bean itself, which means you are not really adding any acid to the soil with these grounds. In experiments on decomposing coffee grounds, they were found to be between pH 5.26 (mildly acidic) and 8.4.
Some varieties of fresh coffee grounds are acidic (they have an alkaline reserve of 5.3 on the pH scale), so it is tempting to think that using coffee grinds in your garden will lower the soil pH. However, there are a couple of things to consider before mixing plants with coffee when gardening. It is thought that decomposing grounds offer some protection against some fungal conditions, although more research is needed.
The best way in gardening to use coffee grounds is to add them to your compost pile or compost tumbler.
Does Lime Cause Acidic Soil?
Lime is sometimes used in the garden as a soil amendment to raise soil pH, creating a more basic soil over time. It does not make your soil acidic.
This is because lime “sweetens” the soil and helps to counteract the acidic conditions found in many gardening areas.
Lime material can be used in an area that has naturally acidic soil, or where a more acidic soil has been created by over-fertilization.
The word lime is somewhat misleading, since it is not a type of plant.
It is a naturally occurring substance known as calcium carbonate that is extracted from limestone.
We have established that there are certain plants that thrive best in slightly acidic soil. These plants include, but are not limited to, common garden vegetables, primroses, garden lilies, lupines and camellias.
Always start by figuring out the soil type by scooping some up with your hands. If you feel that it is loose and airy, mix it with some organic material — like compost, sphagnum peat moss or manure, for example — in order to reduce its pH and make it more acidic.
If you feel that the soil is more compact or dense, use iron sulfate or some elemental sulfur to reduce the pH of your soil.
This should be followed by a soil pH test to see whether the pH levels still need adjusting or whether you have reached the desired pH.
Fertilizers can also be used to acidify soil. Look out for fertilizers that contain ammonium nitrate and ammonium sulfate. They are great acidifying fertilizers.
There you have it, a brief summary of how to acidify soil — not rocket science right? We hope that the above written details are helpful in your quest to make your garden soil more acidic without causing significant harm to already planted shrubs.
Try not to overthink it. Happy planting!