How To Amend Your Soil’s pH with Compost (Easiest Method)

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Let’s be serious for a second, soil pH isn’t that important for the average gardener. Unless you have something very wrong with your soil pH and you’re trying to diagnose an issue, you probably don’t need to test it.

But you probably already know that.

You want to test your soil’s pH because you’re an optimizer. Gardening is more than just a simple hobby to you and you want to understand everything so you can make it the best it can possibly be. Add to that the fact that using soil test pH strips is just super cool and makes you feel like a scientist and you have a fun afternoon ahead of you!

However, that’s not to say that testing your soil’s pH is without merit. There are, in fact, several advantages to knowing your soil’s pH and amending it.

Soil pH: The Basics

In layman’s terms, pH is the test of how acidic or basic something is. Slightly more technically, it is an inverse logarithmic scale that is inversely proportional to the concentration of hydrogen ions in a solution. It is a scale that runs from 0 (the most acidic) to 14 (the most basic). An example of a pH 0 material would be battery acid and a substance with a pH of 14 would be lye.

Soil pH in an area where people are likely to live and garden typically does not vary widely in acidity (at least, as far as numbers go). Soil pH typically ranges from 3.5 to 10 with the majority of soils being roughly neutral (around 7). However, because it is a logarithmic scale, remember that each change in numbers is a 10-fold change (similar to how earthquakes work) For example, soil with a pH of 4 is 10x as acidic as soil with a pH of 5 but 100x as acidic as soil with a pH of 6. So small changes can add up fast.

Many gardeners use the word “alkaline” in exchange for “basic” when talking about the pH of their soil. As such, plants are typically divided into plants that thrive is acidic soil and plants that thrive in alkaline soil.

The optimum pH for soil is generally considered to fall somewhere between 6-7 (slightly acidic). Anything lower than 5.6 and many plants struggles to thrive.

The main advantages to knowing your soil pH are two-fold: you plant plants that will thrive in your given pH or, if things are really out of whack, you can make adjustments to make your soil’s pH more hospitable to plants you wish to grow.

How to Test Your Soil’s pH at Home (4 Options)

When it comes to testing your soil, there are several options available to home gardeners. Some are pretty much free and will take a couple of minutes, others can run you hundreds of dollars. Just be sure to choose one that makes sense with the return on investment that you are likely to get.

Option 1: A Soil Test Kit

The most thorough (and expensive) way to get an idea of your soil’s health is to get a soil test kit. These can range from kits like the MySoil kit on Amazon to complex kits that you send off to labs for analysis.

The benefits here are obvious. The MySoil kit, for example, tests not only pH but the presence of 13 other nutrients that plants need to grow and produce. While this provides you with a huge amount of information that can help to perfect your soil, it is probably unnecessary for most hobby gardeners.

Option 2: The Old-School Method

If you simply need a method that will allow you to see if your soil is acidic or alkaline, there is a simple test. Knowing even this much information will typically allow you to select plants that will thrive in your given environment.

Think back to the days in elementary school when you made a volcano out of baking soda and vinegar. This was a prime example of an acid/base reaction and we can use the exact same principles (and ingredients, actually) to test your soil. Here’s how to do it:

1. Make sure your hands are free of contaminants. Getting a handful of dirt and scrubbing it over your hands is a good way to do this.
2. Grab another handful of dirt and pour some vinegar over the top, just enough to wet it. If it fizzes and bubbles (remember the volcano) then it is reacting with your soil and you can be assured that your soil is, to some extent, alkaline.
3. If you got no results from the vinegar test, clean off your hands and grab another handful of soil. Mix in a healthy sprinkling of baking soda then wet the mixture with distilled water. If it bubbles up, the reaction tells you that your soil is acidic.

More likely than not, you won’t see much of a reaction at all. If you don’t you can feel fairly comfortable that your soil is either neutral or very close to neutral and probably doesn’t need much pH mediation.

Option 3: Soil pH Test Strips

Of all the methods available, soil pH test strips (in my opinion) will give you the most bang for your buck. They are inexpensive, easy to use, and give you more precise information than dumping vinegar over a handful of dirt.

The method of using soil pH test strips at home is fairly straight forward.

1. Get yourself some dirt in a container that isn’t likely to be contaminated with anything that matters (no food waste, etc.)
2. Wet the dirt with distilled water
3. Touch the soil pH test strip to the wet dirt (if should change color)
4. Compare the strip to the color wheel on the package to determine the pH of your soil

That’s all there is to it! Since you normally get test strips in a package containing hundreds of strips, go wild and test a multitude of areas including the top of your soil, near root systems, in your flower beds, under your compost pile, etc. You might be surprised to find that different areas of your land have drastically different pHs. But don’t worry, we’ll see at the end of this article that we can use the same compost to amend both basic and acidic soils.

The Soil pH Test Strips I Use:

Option 4: pH Probe

If you are serious about testing and optimizing your soil’s pH, it may be worth it for you to invest in a pH meter. With a meter, testing your pH becomes as simple as sticking the probe into the ground and taking a reading.

This comes with the obvious advantage of speed and convenience but with the added expense. If you are going to be testing your soil often, a probe will be much more cost-effective than a soil test kit. However, if you just want to test your soil out of curiosity or once every year or so, soil pH test strips are probably a better option.

Recommended Soil pH Testing Probe

How Does Soil End Up Acidic/Basic?

So you’ve used your soil test pH strips, find out what type of soil you have, and now want to know what to do with that information. Well, unfortunately, we need a bit more information before we can come up with a plan of action. The first step to fixing your soil is to figure out how exactly it ended up the way it is. If your soil is unusually acidic or alkaline, there is always a reason. However, this reason is typically endemic to your region and not because of something you did.

What affects soil pH:

• Origin Material: The most common and obvious reason that soil ends up acidic (or alkaline, but we’ll use acidic in this example) is the type of material that the soil is made of. For example, soil in a peat bog or a long-standing pine forest tends to be more acidic because the materials that have broken down to form soil were more acidic themselves. Depending on where you live, the types of rocks that break down into soil may also affect pH. Rocks such as limestone typically break down and alkalize the soil while siliceous rocks such as lava rocks tend to acidify it.
• Rainfall or Irrigation: It may surprise you that excessive watering or rainfall can actually be harmful to your soil itself in the long term. Too much water moving through the soil tends to dissolve and wash away (“leach” is the gardening term) necessary nutrients such as calcium, potassium, and magnesium. These nutrients play a vital role in preventing the soil from becoming acidic and when they’re gone, the pH beings to slowly decline. This is typically not a result of just watering your lawn, however. Over the course of many many years, soil that is not amended ends up more basic or acidic.
• Fertilizers and Additives: The last common way that your soil ends up with an altered pH is through the addition of fertilizers. Fertilizers and additives will typically cause your soil to end up acidic rather than basic. This is because most synthetic fertilizers are ammonia-based, meaning they are high in nitrogen. Nitrogen increases the acidity of your soil.

Now that we understand how your soil got into the state that it’s in, we should have a little more information on how we’re going to address this issue. But first, why do we need to address it at all?

How Soil pH Affects Nutrient Availability

The only reason to care about the pH of your soil is if you care about the plants that are trying to grow in it. Not worried about a garden or your lawn? Forget about fixing your pH.

The reason that pH has such a large influence is that it has the ability to affect the nutrients that are available to plants. Every nutrient has a pH range that is more easily taken up by plants and, if the soil is outside of this range, plant growth suffers accordingly.

The reason that pH affects nutrient availability is that it strongly affects what will be soluble. For example, Phosphorus is one of three macronutrients that all plants need (the other two being Nitrogen and Potassium, making up the moniker NPK). For phosphorus to be soluble (dissolvable in water) the pH of the soil should optimally be between 6 and 7.5. Outside of that range and plants will not be able to take it up in the water.

Phosphorus is just one example but every single nutrient has a pH range where it is more readily utilized by growing plants. Without boring you with a large and unnecessary chart, suffice it to say that if you stay within a pH of 6-7 your plants will be able to get everything they need.

Using Compost to Adjust your Soil’s pH

When it comes to adjusting the pH of your soil, think of it as fixing the balance of hydrogen ions. If your soil is too acidic, let’s add something to it that is basic or block what makes it acidic (and vice versa).

Whether or not you are trying to fix your soil’s pH, learning to compost, and then adding compost to your garden is a great way to improve the health of your soil. However, compost is particularly helpful in cases of acidic or pH-imbalanced soil as it acts as a “buffer” essentially blunting the effects of pH that is out of whack. This is another reason I recommend using either soil test pH strips or a probe because you can test your soil after every remediation without spending an arm or a leg.

Before trying anything else to fix your pH, you will want to give the compost a season or two to work on your soil. Adding and incorporating a couple of inches of fresh compost a year is typically enough to amend all but the most deviant soils.

One of the reasons that you should stick with compost (at least at first) is because it will slowly fix your pH. If you try more aggressive methods (like those pushed in many books) you run the risk of killing your soil’s microbiome. Most bacteria and fungi have a specific range in which they like to function (5.5-8 in the case of compost bacteria). Change it too fast and you can wipe out this biome, effectively destroying your soil and making it much more difficult to fix.

If compost fails to fix your pH problem (or you don’t want to try…) there are a couple of well-known and tested alternatives that can fix your problems:

Fixing acidic soil with lime: Lime is a common additive for fixing acidic soils. Just sprinkle it over the top of your soil and let it works its way in through watering or manual incorporation. Adding lime to your soil should only be considered if you have significantly acidic soil that the compost failed to fix. Do not add lime to your compost as it will slow down decomposition.

Fixing alkaline soil with sulfur: Sulfur can be used for basic soils the same way that lime is used for acidic ones. Sprinkle it on and incorporate it in small batches over a period of time to slowly move your soil’s pH in the direction you want.

It is much more common for soil to be acidic than basic. Probably because people don’t farm or grow things where it’s arid.

Conclusion

While you should never try a fertilizer or lime/sulfur remediation before significant testing, composting is a practice that is beneficial to your soil no matter what. So, by all means, get some soil pH test strips or a probe and learn what they can tell you, but never stop composting!