Having a proper soil pH is a crucial part of maintaining plant health. Soil acidifiers can be a powerful tool for reaching and maintaining the soil pH your plants require. But how often should you apply a soil acidifier to keep your pH at the desired level?
You should use a soil acidifier every 60 days while lowering the soil pH. After the pH has reached the desired level, the soil acidifier should be used two to three times each year. Repeat pH testing of the soil will determine how often to reapply your specific acidifier.
This article will discuss how long soil acidifiers last when you should use them, and the types and applications of soil acidifiers.
How Long Does Soil Acidifier Last?
Soil acidifier lasts about three to four months. The frequency of soil acidifier application is determined by the type of acidifier you use and the texture of your soil. Before adding an acidifier, test the soil’s pH level to ensure more amendment is necessary.
Most soil acidifiers will need to be applied two or three times a year to maintain the pH level of your soil. As you are lowering the pH initially, applications may be more frequent.
You should retest your soil pH every three or four months and use the results to determine when to add more acidifiers. For step-by-step instructions on how to test the pH of your soil, take a look at my article on dry soil nutrient testing: Does Soil Need to Be Dry for Nutrient Testing?
Different types of soil acidifiers last different amounts of time, so the type you choose will affect how long the effects will last. For example, iron sulfate works very quickly, so you will need to apply it more often during the growing season but do not need to apply it in the winter.
On the other hand, granular sulfur takes a while to work, so you will need to use it less frequently but year-round so that it has time to take effect before the growing season.
In addition to the type of soil acidifier you use, the texture of your soil will also determine how long the effects will last. Lighter soil high in sand and silt will absorb soil acidifier more readily than clay-based soil.
Over time, you will learn the frequency necessary for your unique acidifier and soil combination and may need to test your soil less frequently. You should still test at least once a year.
When Should You Use a Soil Acidifier?
You should use a soil acidifier when you need to lower the pH of your soil to accommodate certain plants. Use soil pH tests to determine if a soil acidifier is necessary for your garden.
Make sure to research the plants that you are bringing into your garden so you know the pH labels each plant requires.
Soil Acidifier Can Help Make the pH Neutral
Soil that is too alkaline, or has a pH above 7, is difficult for most plants to survive in because there are not enough nutrients available. Alkaline soil is low in iron, manganese, copper, zinc, and phosphorus. You can add a soil acidifier to bring the soil pH back into balance.
The amount of acidifier needed depends on how far the current soil pH is from neutral, but generally, making a soil pH neutral takes less acidifier than making the soil acidic. In addition, it generally needs less frequent application.
However, some regions in the US tend to have naturally alkaline soils. After some time, the soil will return to its alkaline state, requiring a strategic plan and scheduling of soil acidifier application.
Remember that potted soil may need less frequent applications of soil acidifiers because there aren’t as many environmental factors pulling the soil back to an alkaline level.
Certain Plants Require Acidic Soil
Although most plants do best in soil with an almost neutral pH, some require more acidic soil than normal, which has a different set of available nutrients than neutral soil.
Acidic soil is high in iron but low in many other nutrients, including phosphorus, calcium, and magnesium. Only plants adapted to acidic soil will be able to survive with these low nutrient levels.
Plants that need more acidic soil include:
- Azaleas
- Blueberries
- Holly
- Hydrangeas
- Rhododendrons
If you have a group of plants that require acidic soil, it is best to group them together in your garden. Isolating them in their own bed can help prevent the soil acidifier from migrating to other plants that cannot tolerate acidic soil.
Types of Soil Acidifiers
There are several types of soil acidifiers to choose from. The time it takes to impact soil acidity and the effects on specific nutrients can help you decide which acidifier is best for your garden.
Some common soil acidifiers to choose from include:
- Aluminum sulfate: This substance is a good choice if you need an acidifier that works fast. However, the effects wear off quickly, requiring more frequent application. Aluminum sulfate should also only be used around the base of plants to prevent potential aluminum water toxicity.
- Ammonium sulfate: This acidifier also works very quickly, so you should add it in small amounts until the desired pH is reached. It also increases sulfur levels in the soil.
- Iron sulfate: This formula is best used to treat soil with low iron levels. It works very quickly, providing pH changes in a month or less. Acidic soil is often high in iron, so a nutrient test may be helpful to make sure the iron levels in your soil do not get too high. Iron sulfate can be added as a granular amendment or water-dispersible liquid.
- Peat: Adding peat to the soil is a traditional method of increasing acidity, though it is becoming less popular due to its environmental impact. Peat doesn’t lower the soil pH as drastically as the other options in this list, so it is only useful for small adjustments. It also doesn’t add any nutrients to the soil, so you may need additional amendments to address low nutrient levels.
- Sulfur: The effectiveness of sulfur as a soil acidifier depends on the type you use. A study conducted by the University of Florida found that water-dispersible works much more quickly than granular sulfur. Water-dispersable sulfur can make your soil more acidic within two months, while granular sulfur can take up to a year to significantly affect the pH of your soil.
Applying Soil Acidifier
The application of soil acidifiers depends on whether you are prepping your garden for the upcoming season or amending plants that are already in the ground. While the exact amount of acidifier varies based on the type you use, the application process is the same.
Apply Soil Acidifier to Soil Before Planting
Before applying a soil acidifier, you need to consider how much time it will take to see a drop in the pH levels. Most longer-lasting soil acidifiers should be applied in the fall to have time to gradually lower the pH before the growing season in spring.
Soil acidifier should be mixed into the top layer of your soil, at least six inches (15 cm) deep. Follow the instructions on the product label of your chosen acidifier to determine how much to add, depending on the size of your garden or raised bed.
Apply Soil Acidifier to Existing Plants
It is never too late to apply a soil acidifier, even if your plant is already in the ground. However, be sure to use a fast-acting acidifier so that it has time to change the soil pH within the growing season.
There are two ways to introduce soil acidifiers to existing plants:
- Granular acidifiers provide the easiest application, with small pellets you sprinkle on the soil. Make sure to apply the acidifier directly on top of the dirt, removing any topsoil, mulch, or rocks on top. Do not apply granular acidifiers beyond the edges of your plants. This is especially important if there are other plants in your garden that you do not want to affect.
- Water-dispersable acidifiers are absorbed quickly to help speed up soil pH changes. Mix acidifiers in water and add the mixture to the drip line. Alternatively, you can apply it directly to the soil around your plants using a watering can.
If you want to learn more about how long soil acidifier takes to work, check out my article. I’ll specifically discuss what soil acidifier is, how it works, and why you might want to make your soil more acidic. I’ll also discuss some troubleshooting information for using soil acidifiers: How Long Does Soil Acidifier Take to Work
Conclusion
You should use a soil acidifier every two months to lower your soil’s pH. When pH tests indicate that you have reached the desired pH, you should use an acidifier two to three times a year to maintain a suitable level for your plants.
On average, soil acidifier lasts two to three months, but the type of acidifier you choose and the texture of your soil will affect how long the effects will last.
