Some plants, such as hydrangea and azalea, prefer soil that is acidic, but what can you do if that's not what you have available? Don't worry, you don't have to be condemned to a life without the plants you dream of having. Instead, you can learn how to make your soil acidic so you can grow a garden full of the plants you want.
If your soil isn’t acidic enough or it has been treated with lime, you'll need to use a few tricks to adjust the pH to make those acid-loving plants happy. With that said, there's lots of advice out there on the internet that could lead you astray.
In this guide, we'll show you the right way to lower your soil pH depending on the type of soil you have, and what you need to avoid. Ready to get started? Let’s take a look at how to make your soil acidic.
What is pH?
pH is the indication of how alkaline or acidic your soil is. The closer the number gets to 0, the more acidic the soil is. The closer the number is to 14, the more alkaline the soil is. If the number is around 7, such 6.7 or 7.4, you can consider your soil more in the neutral range.
- 0-6.9 pH: Acid
- 7: Neutral
- 7.1-14: Alkaline
Plants That Need Acidic Soil
There are probably more acid-loving plants out there than you realize.
- Pine Trees
- Green Peppers
- Calla Lilies
- Bleeding Heart
- Crepe Myrtle
While many of these plants can survive in soil that's a bit more neutral, if you really want them to be productive, you need to give them the acid they crave.
How to Test the pH Level in Your Soil
Before you do anything to change your soil's pH level, test your soil. You don't want to mess with your soil's balance if you aren't sure where you are starting.
You can get your soil professionally tested for the most accurate results, but you can also do it yourself. If you feel comfortable with a bit of variance in the accuracy of the test, there are several ways for you to get a reading at home.
Gardeners should plan to check their pH level every year near the base of the plants. What you grow each year changes the composition of your soil, so for best results, plan to either use a professional or test at home yearly.
1. Paper Strips
Paper strips are one of the cheapest test choices, and they can let you know if your soil is more acidic or basic. It won't tell you the exact measurement, but you'll at least get a general idea.
2. Home Testing Kits
Another option is an at-home test that can give you a pH number for your soil. These kits vary in price and accuracy. Most of them use a small sample of earth mixed with water and a chemical to give you your results.
You can also use digital meters to test your soil. These tend to be more accurate, but some of them can be pricey, so they're best for people who need to check a lot of soil.
4. Vinegar & Baking Soda
You don't have to go out and buy a kit if you're only trying to figure out if your soil is closer to acid or basic. The vinegar and baking soda test is a reliable way to get a general idea. It's also a neat experiment to do with the kids. Keep in mind that this testing is rudimentary; you won't get exact numbers.
To do this test, take a cup of soil and divide it into two containers. Add vinegar to one container and baking soda and water to the other, and wait to see which one fizzes. If the vinegar fizzes, your soil is basic or alkaline. If the baking soda fizzes, then your soil is acidic.
Figure Out Your Soil Type
Now that you know whether or not your soil is acidic, you have to figure out your soil type, which is different than determining the pH level. Understanding the type of soil you have will help you decide which method you want to use.
This information matters because well-draining soil that is light and loose makes acidification easier. Loose soil benefits from organic compounds that add acid to the ground as it slowly breaks down. Soil that doesn't drain well, such as clay, makes it a bit harder to acidify because adding organic material makes it more alkaline. Weird, right?
How to Make Soil Acidic
It’s time to make your soil acidic, and how you do that will vary based on your soil type. There are a few ways to do this, so we broke each option down to help you decide which method is the right one for your garden.
Increasing Acid in Loose Soil
If you happen to have loose soil, increasing the acid isn't too hard. Your best bet is to use organic material because it acidifies the ground as the materials break down over time. Keep in mind that you need to use large amounts of organic matter to bring down the pH level.
So, what can you add to the soil? A few choices are:
- Compost and composted manure
- Composted oak leaves
- Sphagnum peat moss
Peat moss is one of the most popular picks for small-scale gardeners because it has a pH level of around 3.0 to 4.5. It will slightly acidify the soil while adding organic materials as well. Try adding 2-3 inches of peat moss to your soil and tilling it to a depth of 6-8 inches. This amendment will last for around two years, but it's not cost effective for large gardens.
Increasing Acid in Clay Soil
Making clay soil acidic is a bit harder because adding organic materials to dense soil raises pH. That's because clay soil retains moisture, which leads to more alkaline soil.
Gardeners need to add elemental sulfur to soil that's heavily compacted. Another choice is iron sulfate, which does the same thing as elemental sulfur. Let’s take a look at both options.
1. Adding Elemental Sulfur
Elemental sulfur takes time to react, so it’s best if you add it to the soil the year before planting. That means you have to plan ahead. Try soil testing in the fall after your fall gardening is complete and mixing in the elemental sulfur before winter arrives. It needs warm soil to get going, so the process will pause once the soil gets cold and pick back up in the spring.
This amendment works because it turns the bacteria in the soil into sulfuric acid. If your current soil pH level is at a 7, you will need to add 2 pounds of elemental sulfur per 100 square feet to bring the level down to 4.5.
Elemental sulfur is the best choice if you already have flowers or plants in the ground. It's slow-acting, so it won't shock or harm your plants, and it's hard to make mistakes with the doses. Try to work it into the soil gently with your hands to avoid disrupting the root system.
2. Adding Iron Sulfate
Another way to amend clay soil is to add iron sulfate. This method relies on a chemical reaction to create acid in the soil. It doesn't require the right conditions to create the result that you want as elemental sulfur does, plus it produces the desired effects much faster, taking only 3-4 weeks rather than months.
You'll need around 10 pounds of iron sulfate for every 100 square feet to reduce your pH level by one unit. So, to reduce your pH level from 6 to 4, you'll need 20 pounds per 100 square feet. However, those two applications have to split into two, spaced 1-2 months apart so that the soil has time to absorb it slowly.
Try an Ammonia Fertilizer
Some gardeners swear by using an ammonia-based fertilizer to acidify the soil in their garden beds. It’s the best choice if you have an acid-loving plant nestled amongst plants that prefer neutral ground. In those cases, amending the entire garden bed isn’t a good idea, so use an acid fertilizer.
Some of the most common fertilizers contain ammonia sulfate or sulfur-coated urea. Both of those can increase the soil acid level.
Be sure to stay away from calcium nitrate and potassium nitrate if you’re trying to increase acid in your soil. Even though they are technically ammonia-based, they’ll raise the pH level, making your soil more alkaline.
Does Vinegar Make Soil Acidic?
By now, you’ve probably read an article or two on Pinterest that tells you vinegar makes the soil acidic, but is it a good thing to use?
It’s true; vinegar will lower the pH level in your soil immediately, but that’s not always a good thing if you already have plants in the ground. Dramatically changing your soil, in general, isn’t necessarily a good thing because it can kill off beneficial soil organisms.
If you want a quick fix, you can try watering your plants with a solution that is two tablespoons of vinegar to one gallon of water. As you can tell, that's very diluted! It works well with container plants in particular.
Note that while vinegar does make your soil more acidic, it goes away quickly too, so it’s not a long-term solution.
Use Lime to Increase The pH Level
This guide is about making the soil acidic, so why are we talking about how to increase the pH level?
Well, sometimes we do our job too well, and we're left with soil that is too acidic for the plants you want to grow. If that happens, you need to alkalize your soil by adding lime around the base of your plants.
Changing your soil's pH level doesn't happen quickly. The safest choices are using compost, peat moss, or elemental sulfur because they take time to work. It's best if you make the applications in the fall or early spring before planting to amend your soil without harming your plants. Remember that an ammonia-based fertilizer is the best choice if you want to modify the ground around a few plants rather than your entire garden bed.
With the proper planning and method, your acid-loving plants will find their happy place in your garden bed.