In chemistry, pH is a measure of how acidic or basic a substance is. The pH scale ranges from 0 to 14 - a pH near 0 is extremely acidic, near 14 is very basic and at 7 it is perfectly neutral. In gardening and horticulture, the pH of the soil used for growing plants can have serious effects on the health and growth of the plant. While most plants tolerate a pH of around 6.0-7.5, some grow best in a narrow pH range, so professional gardeners should learn the basics of soil pH management. See the step below to start learning how to lower the soil pH.
Steps
Part 1 of 3: Performing a pH Test
Step 1. Test the pH of the soil
Before adding anything that can alter the pH of the soil, always be sure to test it out to know how much it differs from the ideal value. You can buy a test kit at any nursery or take a sample to be professionally analyzed.
Step 2. Drill five small holes in the planting area
The pH of your garden soil is easy to determine with a commercial pH test, usually sold at hardware or garden supply stores, and quite inexpensive. To get started, we recommend that you take a sample from the area to be tested. Dig five small holes (about 20cm deep). Select random locations within the zone - this way, you will get an "average" pH value of your soil. Do not keep the soil removed from the creation of the holes.
Note that the instructions in this section are generalized - you must use the instructions included with your specific pH test kit
Step 3. Take a sample from each hole
Next, use your shovel or spade to take a thin "slice" from the side of each hole. This section should be crescent-shaped and about 1.5cm thick. Try to prepare a sample of about the same size for each hole. Add your samples to a single clean, dry bucket.
Try to collect enough soil from each sample, about a liter or more in total. For most test methods, this is more than enough
Step 4. Mix the soils in the bucket and spread them over the newspaper to dry
Leave your soil to dry until you are no longer able to detect its moisture.
It is important to make sure the soil is completely dry before proceeding - moisture can cause an inaccurate pH reading
Step 5. Use the test kit to determine the precise pH level of your soil
The method varies depending on the type of kit you own. For many of the more common kits, you can put a small amount of your medium in an included tube, add a few drops of liquid solution, mix by swirling, and let the mixture settle for a few hours. Eventually, the color of the solution should change - by comparing the color of the solution with a chart provided with the kit, you can determine the pH of your soil.
There are other types of kits as well, so be sure to use the instructions provided. For example, some modern electronic test kits determine the pH of a soil almost instantaneously with a metal probe
Part 2 of 3: Using Techniques to Lower the pH
Step 1. Add organic matter
Many types of organic matter, such as compost, manure, and acidic mulches (e.g. pine needles) can gradually lower the pH of the soil over time. As organic matter decomposes, bacteria and other microbes grow and feed on it, creating acid by-products in the process. Since organic matter takes time to decompose and change the soil, this option is fine for long-term goals, but will not give you decisive results immediately. Many gardeners opt to add organic matter to the soil annually for a gradual, mild pH-lowering effect.
Organic matter can also give the soil other benefits - in particular, it improves drainage and aeration
Step 2. Add aluminum sulfate
To lower the pH quickly, you don't have to rely on a slow and gradual decay of organic matter. Instead, try using one of the many siliceous soil additives available at your local garden store. Among these additives, aluminum sulfate is one of the fastest-acting options available. Aluminum sulfate produces acidity in the soil as soon as it melts, which, for gardening uses, means it basically works instantly. For this reason, aluminum sulfate is a great choice for lowering the pH quickly.
Depending on the starting pH of your soil, the amount of aluminum sulfate you should use can vary greatly. Very generally, about 1.2 kilos of aluminum sulfate should be used to lower the pH of a 9,000 cm ^ 2 piece of soil by one unit (for example, from 7.0 to 6.0 or 6.0. to 5, 0, etc.). However, using too much additive can be harmful to your system, so you may want to consult an online resource (like this one here) for more precise information on its use
Step 3. Add some sulfur, a very useful additive for lowering the pH of the soil
Compared to aluminum sulfate, sulfur is generally cheaper, more potent (in terms of the amount needed) and slower acting. This is because the sulfur has to be metabolized by the bacteria in the soil to be converted into sulfuric acid, which takes time. Depending on the soil moisture, the amount of bacteria present and the temperature, sulfur can take up to several months to produce a noticeable effect in the soil.
As noted above, compared to aluminum sulfate, a relatively small amount of pure sublimate sulfur is generally required to produce an equivalent pH change. In general, about one kilogram of sulfur will be needed to lower the pH of a 9,000 cm ^ 2 piece of soil by one unit. For more precise information on use, consult an online resource (like this one)
Step 4. Add urea-coated sulfur
Like sulfur and aluminum sulfate, this additive can also increase the acidity of the soil over time (lowering its pH). As an additive, urea is quite rapid, producing some effects after just a week or two after being introduced into the soil. Urea-coated sulfur is a common ingredient in many fertilizers, so if you had already planned to fertilize plants, you could save yourself the trouble of finding additional soil apart by simply taking a fertilizer containing this type of urea.
The content of urea-coated sulfur varies from fertilizer to fertilizer, so you will need to consult the instructions supplied with the fertilizer to determine the right amount to use for your needs
Step 5. Add another acidic additive
In addition to the additives listed above, many other substances can lower the pH of the soil. Many of these substances are often included in certain fertilizer blends, while others are sold individually. The time and amount required can vary greatly for each, so you will need to consult the instructions on the package or speak to a garden store expert. The additives that can lower the pH of the soil are:
- Diammonium phosphate
- Ferric sulphate
- Peat
- Ammonium nitrate
Step 6. Grow alkaline-tolerant plants
If your soil is too alkaline (basic) to grow plants that require acidic soil, growing alkaline-loving plants can gradually lower the pH of your soil. As the plant grows, matures and decays, the organic matter it returns to the soil will promote the growth of bacteria and gradually lower the soil's pH level (just like adding organic matter in the form of mulch or manure). This method is generally one of the slowest ways to lower the pH of the soil, as the plant must grow to begin depositing organic matter in the soil. Some examples of alkaline-tolerant plants:
- Some evergreen shrubs (e.g. boxwood, California lilac)
- Some deciduous shrubs (e.g. lilac, angel flower, forsythia)
- Some perennials (e.g. hellebori)
Part 3 of 3: Knowing When to Decrease the pH of the Soil
Step 1. Lower the soil pH for shrubs such as rhododendrons and azaleas
Some types of flowering shrubs, such as rhododendron and azalea plants, require enough acidic soil to grow properly. These plants are often native to areas with a high amount of rainfall, such as the Pacific Northwest region of the United States (frequent rainfall generally lowers the soil pH). For these types of shrubs, a pH range of around 4.5-5.5 is optimal. However, high pH levels around 6.0 are usually acceptable.
Step 2. Lower the soil pH for flowers such as begonias and hydrangeas
Many bright flowers, such as petunias and begonias, grow best in acidic soils. For some of these flowers, changing the acidity of the soil from "slightly" to "very" acidic can produce a visible change in the color of the flower. For example, growing a hydrangea in soil with a pH level of around 6.0-6.2 will produce a plant with pink flowers, while lowering the pH to around 5.2-5.5 will result in a plant with flowers. purple / blue.
The blue color of low pH hydrangeas comes from chemical aluminum. When the soil pH is low, it is easier for hydrangea to absorb aluminum from the soil, which manifests itself in the flower petals
Step 3. Lower the soil pH for evergreen trees
Many needled evergreen trees grow in slightly acidic soil. For example, spruces, balsamic firs, and all pines thrive in soils with a pH level of around 5.5-6.0. Additionally, needles from these types of trees can be introduced into neutral or alkaline soil such as organic matter that lowers the pH of the soil in the form of a superficial deposit of needles.
Step 4. Lower the soil pH for some berries
Perhaps the best known acid-loving plant is blueberry, which thrives in highly acidic soils (generally 4.0-5.0 is ideal). However, numerous other berry species prefer an acidic soil. For example, blueberries grow best at a pH level of 4, 2 to 5, 0, while gooseberries, currants and elderberries grow best at around 5, 5-6, 5 levels.
Step 5. Lower the pH to just below neutral for ferns
Most garden fern varieties prefer soil pH levels below 7.0 - even those that prefer alkaline soils can usually tolerate slightly acidic soils. For example, Maidenhair Ferns prefer soil with a pH of around 7.0-8.0, but they can also grow in soils with levels around 6.0. Some ferns can also tolerate soils with a low pH of 4.0..
Step 6. Consult a gardening resource for a complete list of acid-loving plants
The number of plants that survive or thrive in low pH soils is too great to list in this article. For more information, it is recommended that you consult a comprehensive source of botany. They can usually be found at garden stores or specialized bookstores, although there are other sources available. For example, the official website of the "Old Farmer's Almanac" contains a table that lists the pH preferences of different types of plants (you can access it here).
Advice
- Some soil altering chemicals are available as sprays.
- It is important not to abuse chemicals to alter the soil, because they can have long-term negative effects on the soil, as well as on the environment.
- Plants that grow in soil with an unsuitable pH level will not thrive, as some nutrients will be bound by the soil and, therefore, will not be available to the plant.
- The effects of elemental sulfur will last for several seasons.
- Elemental sulfur is generally best applied in the spring months, and is very difficult to use when the plants are already in place.
- Soil pH can affect everything from drainage to erosion rate.
- Use natural compost whenever possible. This benefits the plants by increasing the available nutrients. Composting is a great way to recycle grass clippings and kitchen scraps.
- Compost and elemental sulfur facilitate biological reactions, while aluminum and iron sulphate cause chemical reactions.
Warnings
- Too much aluminum sulfate can poison the soil.
- If urea, aluminum sulfate or sulfur is spilled on the leaves of the plant, rinse with plenty of clean water. These substances, if they land on the leaves of the plant, can "burn" them, causing unsightly damage.
