You’ve done everything right, from using the best watering techniques to using the best organic fertilizers, yet your blueberries just aren’t thriving.
This is a far more common issue than you might imagine, and it’s almost always down to the soil pH. Some gardens have neutral soils, some have alkaline soils, and some have acidic soils.
Most plants in your garden soil need at least slightly acidic soil, and a soil pH range of 6.5 will be perfect for most of your garden’s denizens.
However, some require a more acidic environment, meaning you must amend your soil to lower its pH.
Acid Soil: How To Make Soil More Acidic
If you look around online, you’ll find many websites give bad advice on soil pH, usually listing pH levels a full point lower than they should be.
For that reason, let’s begin by looking at how soil pH is classified, then get into the whys and hows of making the soil more acidic.
Understanding Soil pH
The abbreviation pH stands for “potential hydrogen” and tells us a very critical detail about your soil’s quality.
The pH can affect how easy it is for plants to absorb nutrients, especially iron. It also directly affects nutrient availability needed for healthy plant growth.
While a little counterintuitive, a lower soil pH means more hydrogen ions are present in the soil.
It’s measured on a 14-point scale, and getting the pH off by one full point is enough to kill most life.
Thankfully, plants have a decent pH range, and most can handle a full point range.
Before going further, here’s the classification system for soil pH, along with one or two examples of common items at each level:
- 0.0 to 4.4 – extremely acid (lemons = 2.5, vinegar = 2.0 to 3.0)
- 4.5 to 5.0 – very strong acid (tomatoes = 4.5)
- 5.1 to 5.5 – strongly acid (cabbage = 5.3, asparagus = 5.5)
- 5.6 to 6.0 – moderately acid (potatoes = 5.6)
- 6.1 to 6.5 – slightly acid (cow milk = 6.5)
- 6.6 to 7.3 – neutral (shrimp = 7.0, blood = 7.3)
- 7.4 to 7.8 – slightly alkaline(eggs = 7.6 to 7.8)
- 7.9 to 8.4 – moderately alkaline (seawater = 8.32, baking soda – 8.4)
- 9.5 to 9.0 – strongly alkaline (borax = 9.0)
- 9.1 to 14.0 – very strongly alkaline (ammonia = 11.1, mineral lime = 12.0)
Most plants can thrive in a pH range of 6.1 to 7.0 (slightly acid to neutral), but there are some very notable exceptions.
Why You Might Want More Acidic Soil
There are two reasons why you might want to make the soil pH more acidic.
The first is that you may be adding something to the soil that has raised its pH level and want to restore balance.
If you have too much alkaline soil, the nutrients get washed away or never develop because the soil cannot decompose organic matter. This makes its nutrients less available to plants, limiting their optimal growth.
The second is if you’re planning to grow an acid-loving plant. If you have alkaline soil, your acid-loving plants may suffer nutrient deficiencies. They may also develop iron chlorosis, causing the entire leaves to turn yellow.
The following plants all love more acidic soils:
- Bleeding heart
- Japanese iris
- Pin oak
- Sweet potatoes
- Willow oak
Of course, each of these plants has its own ideal pH range, so be sure to do some research before increasing your soil acidity, so you don’t overdo it.
Testing The Soil
Soil testing is an important step that so many of us tend to skip.
You can purchase soil tests online, and they’re not overly expensive.
A soil test will not only tell you the soil pH but also what nutrients are present and how much there are.
This is a great way to find out what adjustments you might need to make to your fertilizer to ensure the ideal NPK for your plant.
Skipping this step can lead to over or under-amending the soil, potentially doing more harm than good.
Natural Methods To Increase Soil Acidity
Believe it or not, many things you already use or can easily be found at garden centers can increase soil acidity.
Here are natural methods you can use to make the soil acidic, whether it’s for your vegetable garden, flower bed, or container plants.
One of the best methods of increasing soil acidity can be used when you have an acid-loving plant mixed in with more neutral plants.
By using a water-soluble fertilizer designed to boost acidity, you can target the soil around that plant without causing a significant change to the surrounding area.
Be sure to use a weak dilution at first so you can see how these fertilizers affect your plants before committing to a stronger dosage.
Once a popular amendment for blueberries, aluminum sulfate is now used almost exclusively for hydrangeas, as excessive use can contaminate the water supply, where it turns into sulfuric acid.
Repeated applications of this can also result in toxic levels due to the build-up of aluminum in the soil.
Aluminum toxicity is considered a toxic element, making it dangerous around children, so other products, such as ammonium sulfate, have replaced this method.
This product has largely replaced aluminum sulfate as a much safer alternative.
However, you must be careful not to add too much to the soil around your plants.
Ammonium sulfate works quickly, resulting in a drastic shift in soil pH if too much is used, resulting in your plant suffering burns.
While often touted as a great way to increase soil acidity, used coffee grounds actually have very little effect on soil pH levels.
Coffee is quite acidic, but most of the acidity is leached out of your grounds when you brew them, resulting in a pH of around 6.5.
Of course, if your soil is too neutral, coffee grounds can be a great way to add nitrogen to the soil while also reaching that sweet spot.
However, if you’re growing an acid-loving plant, it won’t do much good.
While iron sulfate is usually used for treating iron deficiency in plants, it can also lower the soil pH in larger doses.
One important thing to remember is that you’ll need to follow any instructions carefully, as too much of this product can harm your plants.
However, when dug into the soil, it can provide results in as little as 3 to 4 weeks.
One of the most natural ways you can increase soil acidity is by using fresh organic compost.
The amount of organic matter present will boost soil acidity but with minimal risk to your plants while also providing all sorts of essential nutrients.
How much the compost will affect your soil pH levels will depend on what you put into your compost pile, so you may wish to test it before use so you know how much you’ll need for the desired effect.
Also, keep in mind it can take a while for the homemade compost to do its magic on the soil pH, so you’ll need to be patient, but this also means your plants won’t be shocked by a sudden change.
Peat is often used as an organic soil amendment, and for a good reason.
There are two types of peat moss: peat and sphagnum.
Peat moss will slightly increase soil acidity, while sphagnum peat will make it slightly more neutral.
While you likely won’t be able to add much acidity on its own, peat moss can help you get to the normal 6.5 sweet spots while providing additional organic material for your plants.
Sulfur is an excellent option for increasing soil acidity, as it will continue to work for years after a single application. When applied to the soil, the elemental sulfur combines water and oxygen to form sulfuric acid.
The amount you’ll need for elemental sulfur will depend on your soil test results.
Please note that you’ll have to amend the soil the year before, as it takes some time to begin working.
Since it’s slow-acting, you can use this on any soil type, meaning plants have time to adjust to a lower pH.
Thus, in the summer or early fall, before the growing season, you’ll need it. Dig up the soil, and mix in the sulfur deeper down.
It won’t play well with existing plants; you’ll have to uproot them, and they won’t benefit that same year.
As with all products, pay attention to any instructions on the packaging to get the appropriate measurements and soil depth for that product.
Regular distilled white vinegar is extremely acidic, with a pH of 2.5 to 2.7. Red or white wine vinegar is 2.6 to 2.8, and apple cider vinegar is 3.3 to 3.5.
This solution is a good one for plants in pots. However, on their own, these can all be quite brutal on your plants.
However, when properly diluted, they can be a relatively safe way to increase your soil acidity.
Mix 1 cup of distilled white vinegar (5% percent concentration) with 1 gallon of water to increase acidity.
Try not to splash any onto your plant to avoid potential reactions. Moreover, vinegar solution is also not useful in your large garden because it will disappear when used up.
Other Organic Method
Another example of an effective organic method to make acid soil is adding wood chips to your garden.