Some plants prefer acidic soil. Examples include rhododendrons, azaleas, hydrangeas, and blueberries. If your garden has neutral or alkaline soil, you may have to add a soil amendment to make it acidic enough to grow these acid-loving plants. One great way to increase the acidity of you soil is to mix in some peat moss. This guide explains how to use peat moss to make soil more acidic (lower the pH). I’ll also list some pros and cons of using peat moss. In addition, I’ll outline some peat moss alternatives.
What is Soil pH and Why is it Important?
pH is a measurement of how acidic or basic a substance is. It measures the concentration of hydrogen ions to determine acidity. The pH scale runs from 0-14. 7 is a neutral pH. Anything below 7 is acidic. Anything above 7 is alkaline or basic. Acid loving plants usually prefer a pH range of 4.5-5.5.
It’s important to note that the pH scale is not linear, it’s logarithmic. Each number represents a 10x change. For example, soil with a pH of 5 is 10x more acidic than a pH of 6. It’s important to remember this when adding a pH amendment to your soil. You don’t want to double the amount of peat moss to double the change in pH.
The soil pH can affect a plant’s ability to take in nutrients from the soil. Certain nutrients may become more or less available for the plant depending on the pH. For example, zinc, iron, and manganese become more available when the pH is lower. A plant can become deficient in certain micronutrients if the pH is too high or too low. Iron deficiency is common. Oftentimes, you can correct these nutrient deficiencies by changing the pH of the soil rather than adding more nutrients to the soil.
What is Peat Moss?
Peat moss is Sphagnum moss that has been sitting in a bog for hundreds or thousands of years. Sphagnum decays extremely slowly due to the structure of the cell wall. Bogs also create anaerobic decomposition conditions because there is a lack of oxygen. This is a slower type of decomposition than aerobic decay. Peat moss also acidifies its surroundings, which also slows decomposition.
Peat moss is harvested from bogs, where it has been accumulating and decaying for thousands of years. It is organic matter. It is often used as a soil amendment. Peat moss can be used to increase the acidity of soil. In addition, it helps retain moisture and helps aerate the soil. You can use peat moss in your garden soil or potting mix.
Does Peat Moss Acidify Soil?
Yes. Peat moss does make your soil more acidic. The best peat moss for acidifying soil is Canadian sphagnum peat moss. It has a pH of 3.0- 4.5. This will effectively lower the pH of your soil. To compare, neutral soil has a pH of 7. Alkaline soil usually has a pH of around 7.5-8.
Peat moss isn’t always the best way to lower the pH of your soil. Sometimes it isn’t very strong. Most peat moss has a pH of around 5.5. It will really only increase the acidity slightly. Some peat moss found in garden centers is actually almost neutral.
There are stronger options available. If you really need to make your soil more acidic, you may also have to add some sulfur to your soil. More on that later.
Why Use Peat Moss?
In many places, the natural soil is slightly alkaline. This is often the case when the soil contains lots of limestone. Most plants prefer soil that is neutral to slightly acidic. If your soil is too alkaline, many plants won’t grow well.
One way to solve this issue is to use peat moss to amend the soil. The peat moss will neutralize the limestone. If you add enough, it will make the soil more acidic. You can mix it with your natural soil or potting soil.
The use of peat moss isn’t necessary for every garden. Some soil is naturally acidic. By adding peat moss, you could make your soil too acidic for some plants. There are also plants that prefer alkaline soil.
Before adding peat moss to your soil, it’s a good idea to test the pH. You can pay for a soil test. Some cities offer free or discounted soil testing. You just have to send in some soil samples. You could also buy a pH tester online or at your local garden center.
How Much Peat Moss Do You Need?
The amount of peat moss you’ll need to lower your soil’s pH depends on a number of factors including the current pH of your soil, the target pH, the type of soil you have (sandy soil, loamy soil, clay soil, etc.), and the amount of soil. It’s hard to say exactly how much peat moss you’ll need.
You will need quite a bit of peat moss to lower the pH. It’s not a very strong amendment. You could start with 10-20% of the volume of the soil then test the pH and add more as needed. This would be a good place to start. Chances are, you’ll need a lot more than that. To decrease the pH, you’ll likely need a peat moss to soil ratio of 1:3. 1 part peat moss and 3 parts soil. In some cases, you may need as much as 1:1 ratio.
If you need to change the pH substantially, you’re better off just using a little bit of peat moss and also using a stronger soil amendment such as elemental sulfur or aluminum sulfate.
How to Add Peat Moss To Your Soil?
Start by soaking the dry peat moss in some tap water for a few minutes and allowing it to hydrate. If you choose, you can add a little bit of liquid fertilizer to the water. This will enrich the peat moss with some nutrients. Squeeze out any excess water.
Next mix the peat moss into the top layer of soil. You could mix it in a bucket or just use a shovel to loosen the soil and mix the peat moss in. Alternatively, you can add a layer of peat moss to the top of the soil, like you would add a layer of mulch. Over time, the peat moss will degrade and naturally acidify the soil.
Other Ways to Acidify Soil
Peat moss isn’t the only option. Elemental sulfur and aluminum sulfate are the most common soil additives used decrease the pH of soil.
Between these two, elemental sulfur is the safer option. It is commonly available at garden centers and farm supply stores. The drawback is that it takes a long time to work. The soil also needs to be active and warm. It usually takes 3-6 months for the sulfur to decrease the pH.
Aluminum sulfate works much faster. It will lower the pH of your soil in just a few days or weeks. The drawback is that you have to apply much more of it. It also adds aluminum to your soil, which is toxic to plants.
Another option is ammonium sulfate. This is commonly used on farms. It is used as a fertilizer to add nitrogen to the soil. It can also slowly decrease the pH.
Benefits of Peat Moss
- Peat moss is an excellent soil additive- It can help neutralize alkaline soil or make your soil more acidic if you’re trying to grow acid-loving plants.
- Peat moss helps the soil retain more moisture- It is a spongy material. It soaks up water and then slowly releases it. This water retention helps your plants stay hydrated. You also won’t have to use as much water and you won’t have to water as frequently. This saves you money on your water bill and saves you time.
- Prevents soil compaction- Peat moss helps aerate your soil. It is lightweight and kind of spongy in texture. It helps create air pockets in the soil. This is helpful because your plant roots need oxygen. The roots can also spread more easily when the soil is loose. When the soil becomes compacted, your plants may not get enough water, air, or nutrients to their roots.
- It holds nutrients- Peat moss can prevent essential nutrients such as nitrogen, potassium, and phosphorus from leaching out of the soil or being washed out when you water. It soaks up these nutrients and holds on to them, just like it soaks up moisture.
- Peat moss is sterilized before it is shipped- It won’t contain any weed seeds, fungi, bacteria, or disease that could infect your plants. This makes it perfectly safe to use. It’s a great choice for starting seeds.
- Helps reduce erosion- The peat moss can soak up some moisture and help prevent runoff. This helps the soil stay in place and prevents nutrients from getting washed out.
- It’s natural- Peat moss is a completely natural material. It only contains organic materials. It doesn’t add any chemicals or contaminants to your soil. Over time, it will decay away.
- Long lasting- Peat moss decays pretty slowly. One application will last 2-3 years.
- Fast acting- After you apply peat moss, the pH of the soil will start decline within a couple of weeks. You don’t have to wait too long to plant.
Drawbacks of Peat Moss
The biggest drawback of peat moss is that it isn’t sustainable. It takes hundreds and hundreds of years for peat moss to regenerate after it is harvested. It is being overharvested in many places because it’s so valuable. People love using it in their gardens.
The problem is that, once it’s gone, it won’t come back in our lifetimes. Technically, it is renewable because it will regenerate naturally. Practically, it is a non-renewable resource because it takes so long to generate.
This is a problem because removing the peat moss destroys natural habitat for many birds and insects. Mining of peat moss can also release carbon into the atmosphere. Peat fields or bogs are drained to mine peat moss. They can dry out and catch fire. When they burn, carbon that accumulated there for thousands of years can be released into the atmosphere. This makes peat moss harvesting potentially harmful to the environment. It could contribute to global warming. Some countries have started to restrict or ban the harvest of peat moss to help preserve the peatlands.
Another drawback of peat moss is that is’t fairly expensive. It costs around $4-$5 per cubic foot. That’s around three times the price of other popular soil amendments like compost, manure, or bark mulch. It’s expensive because it needs to be shipped internationally. Most peat moss that is sold in the United States comes from sphagnum peat bogs in Canada.
Peat moss also doesn’t contain many nutrients. You can’t grow directly in peat moss. You need some other type of growing medium. If you soil is low in nutrients, you may need to add some compost or slow release fertilizer along with the peat moss.
Peat moss can also be too acidic for some types of garden plants. You won’t want to treat all of your soil with it. Particularly if you already have acidic soil. You’ll only want to use it if your soil is too alkaline or if you want to grow some acid loving plants.
Some Other Common Soil Amendment Options
There are some alternative soil amendments that can be used to lower the pH of your soil slightly. Coconut coir is one popular option. Coco coir is a type of peat that’s made from coconut. Pine needles and pine bark can also be used.
These materials are not as acidic as peat moss but they could help to acidify the soil slightly. They can also help with water retention and erosion reduction. They perform similarly to peat moss.
My Experience
A few years back, I did a soil test and found that my soil was slightly alkaline. I wanted to plant some blueberries on my homestead and was worried that they wouldn’t grow well because the soil pH was too high.
After some research, I decided to try amending the soil with peat moss. I liked that it is a natural material. When I can avoid it, I don’t like adding chemicals to my soil when I can avoid it. I added some peat moss to the soil where I planned to plant my blueberries. After a couple of weeks, I tested the soil again and found that the pH had dropped. It wasn’t substantial but it had certainly dropped. I decided to add a little more before planting my blueberries. They’re still growing fine to this day.
Peat moss can be used to increase the acidity of your soil. It’s not the fastest or most efficient way to lower the pH but it can work. If you need to lower the pH more substantially, elemental sulfur or aluminum sulfate are also great soil amendments.
Peat moss has many benefits in addition to increasing soil acidity. It helps retain moisture and nutrients, reduce soil compaction, and reduce erosion. It’s also safe to use because it is sterile and natural. The main drawback of peat moss is that it isn’t sustainable because it takes many years to replenish itself. It is being overharvested in parts of the world. It’s also fairly expensive.
Have you used peat moss to lower the pH of your soil? Share your experience in the comments below!
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