How to Make Soil Acidic: 11 Tips to Try
If you need to decrease the alkalinity of the soil in your vegetable garden, here are some ways to make the soil acidic.
Growing an abundant garden requires more than adding compost and putting your plants into the ground at the right time. Your soil is the foundation for your garden, but soil varies widely based on local geology and other factors. If you have alkaline soil, you need to discover how to make soil acidic to encourage certain plants to thrive.
You may remember high school chemistry and the pH scale that runs from 0 to 14. A pH level of 7 represents neutral soil – it is neither alkaline or acidic. The lower the number, the more acidic your soil is. The higher the number, the more alkaline your soil is.
Many gardeners aim for neutral soil; keeping the right pH level for your plants allows your plant to absorb the necessary nutrients from the soil. Also, some plants require different levels of acid or alkalinity, so you should research each plant and its preferences before planting.
Related: 9 Simple Ways to Add Calcium to Soil
When Should You Add More Acid to Your Soil?
It’s not a good idea to add more acid without knowing your plants and soil require it. Adding acid when your soil is already acidic enough for your plants could cause more harm than good.
Here are some reasons you should consider when making your soil acidic.
You Have Nutritional Deficits in Your Plants
When your soil becomes too alkaline, it reduces the plant’s ability to absorb phosphorus, iron, and manganese. Your plant will experience mineral and nutritional deficiencies that will disrupt its overall growth and production.
Acid-loving plants will signal to gardeners that the soil needs to be altered by developing iron chlorosis, a deficiency that leads to the leaf veins or entire leaves turning yellow. If you notice this happening with your plants, it may indicate you need to amend the soil where the plants grow. Another option is to give a supplement with a fertilizer that appeases their acid needs.
You Want to Grow Acid-Loving Plants
If your soil is already balanced and neutral, you may want to acidify your soil to grow more plants that need extra acid. Lowering your plants to a pH range of 5 allows you to grow different landscape plants.
Creating a dedicated bed for the acid-loving plants allows you to alter the soil just for them without affecting the other plants in your garden.
However, don’t get too excited. If your soil goes below a 5, plant nutrients become more soluble and wash away in the rain. A pH level of 4.7 means that bacteria cannot rot organic matter, and fewer nutrients are available for your plants.
You Want to Turn Pink Hydrangeas Blue
If you want to grow hydrangeas, learning how to make the soil acidic makes perfect sense for you. Hydrangeas change color depending on the acidity level of their soil. If you want blue flowers, the pH level needs to be between 5.2 and 5.5, and you have to alter the mineral composition by adding more aluminum.
How to Know if You Have Alkaline or Acidic Soil?
You can’t look at your soil and know your pH range. You need to purchase a soil pH test kit to figure out whether you have acidic or alkaline soil. It’s also possible to test your soil at home without buying tester kits, but a homemade test isn’t guaranteed to be accurate nor give you reliable numbers.
A simple check to use at home is to put some soil from your garden into a jar of vinegar. If the vinegar froths up, then your soil is alkaline, but if it doesn’t, you have acidic or neutral soil.
If you want to be absolutely sure about your soil pH, take a soil sample and bring it to your local extension office. They charge a small fee to complete soil testing that will give you a detailed report about your pH range and nutrient availability for your different plants. This will help you know how to properly fertilize before and after planting.
Which Plants Need Acidic Soil?
The majority of plants in your vegetable garden or landscape plants (along with turf grasses) prefer a pH of around 6.5; this is slightly acidic. However, some plants prefer more acid in the soil to thrive.
Here are some acid-loving plants.
- Azalea
- Gardenia
- Holly
- Rhododendron
- Beech Tree
- Magnolia Tree
- Oak Trees
- Foxglove
- Hydrangea
- Zinnia
- Peppers
- Potatoes
- Rhubarb
- Sweet Potatoes
- Blueberries
- Currants
- Elderberries
- Gooseberries
These are just a few plants that require more acidic soil than others.
How to Make Acidic Soil: 11 Things That Work
1. Add Sulfur to Your Soil
If you used a soil test in the fall before planting, elemental sulfur is an excellent option if you need to make acidic soil. It takes time to gradually lower the soil pH, so adding it the year prior to planting is ideal.
Despite the length of time it takes to increase acidity, elemental sulfur is an excellent option because it lasts for years in the soil. It works better than most other amendments.
It’s crucial that you know the pH of your soil before applying sulfur. Too much sulfur is just as detrimental, and since you bury it deep into the soil, fixing your mistake will take time. Read the directions and follow them closely.
2. Add Iron Sulfate
The next way to make soil acidic is to use iron sulfate, which lowers the pH level. However, it requires a larger volume of product to get the same results as elemental sulfur. If you worry that you may add too much sulfur, iron sulfate could be a great substitute for you.
Many gardeners use iron sulfate to treat symptoms of iron deficiency. This amendment gives faster results than sulfur; expect to see results happening within three to four weeks. However, when over-used, it is harmful.
Applying iron sulfate is easy. You can dig it into the soil around your plants OR create a water-based solution and water it over the plant leaves for easy absorption.
3. Add Compost to Your Soil
Adding compost to your soil is a great option if you prefer to use natural methods to make the soil acidic. Compost is rich in organic matter, and over time, it will decrease the pH of your garden soil.
You also can try making compost tea for your plants. Fill a bucket with compost, and then add water. Let it set for several days before straining out the water and using it to water your plants.
If you know that you want to create more acid with your compost, buy or make ericaceous compost. This is compost with more acidity, and you can make it at home by adding acidic materials, such as:
- Pine Needles
- Oak Leaves
- Vinegar
- Citrus Fruits
Related: Are Orange Peels Good for Compost? The Truth You Need
4. Add Leaf Mold to Your Soil
Leaf mold is decomposed leaves that microorganisms and fungi broke down over time. As leaf mold breaks down, it releases acid that will gradually lower the soil pH range.
It’s easy to start with leaf mold; you only have to add a few leaves to your garden bed and wait several months for them to break down. As they do, the decomposed leaves release acidity into the soil.
The downside is that using leaf mold, just like compost, takes a long time. If you have an urgent matter requiring you to increase acidity levels quickly, leaf mold is not the ideal choice for your garden.
5. Sprinkle Coffee Grounds
Do you have extra coffee grounds laying around? Put them to use in your garden. Coffee grounds are naturally acidic, so adding them to your soil will make it a hospitable environment with lower soil acidity levels.
However, it takes a good amount of coffee grounds to naturally lower your acid pH range. Unless you drink tons of coffee a day, you may need to source your grounds from a local coffee shop, who often save them for local gardeners.
Make sure to thoroughly mix the grounds into your soil. They work as a side dressing, but you also can toss coffee grounds into your compost for an added boost of acid.
Related: 5 Ways to Safely Use Coffee Grounds in Garden
6. Try Sphagnum Peat Moss
Sphagnum peat moss is a bit controversial because it’s considered a non-renewable resource. It comes from large carbon sinks called peat bogs and releases large amounts of stored carbon dioxide when harvested. That contributes to greenhouse gas levels.
If you have no issues using peat moss, it will slightly acidify the soil, while adding more organic material to the garden soil. You need large amounts of peat moss to make a big difference in the pH of your soil.
In general, plan to add four to six inches of peat moss to the topsoil and till it to a depth of six inches. The good thing is one application will last two (maybe three) years!
7. Give Aluminum Sulfate a Try
Aluminum sulfate is another controversial soil amendment to use in your home garden. Gardeners used powdered aluminum sulfate as a soil additive for years to grow blueberries and other plants. It’s easy to use and works quickly around individual plants.
So, what’s wrong?
Well, reports indicate that there is a concern over aluminum toxicity, especially for children. Aluminum absorbs into drinking water, and excessive use of aluminum sulfate may contribute to the contaminated groundwater supply.
So, if you decide to use it, it should be sparingly. Most gardening experts recommend using this product on hydrangeas only because the aluminum helps create vivid blue flowers. Otherwise, other plants handle safer options just as well.
8. Use Pine Needles as Mulch
Another option to giving some more soil acidity to plants is to use pine needles as mulch. The needles are naturally acidic, so they will gradually lower the pH of the soil. At the same time, pine needles take a bit of time to decompose, so they last longer as a mulch than wood chips. That’s an added benefit I appreciate since replacing mulch throughout the growing season is frustrating.
Perhaps best of all, these are free. I’m sure you know someone with pine trees in their backyard who are happy to get rid of the needles in their yard.
9. Use Cottonseed Meal as a Mulch
Cottonseed meal is another additive that you can add to your garden to naturally lower the soil pH. You can use a cottonseed meal as a mulch or add it to your compost before putting it into your garden.
An added benefit is that cottonseed meal is high in nitrogen, a vital nutrient for plants.
10. Use Organic Liquid Feed on Your Garden
Sometimes, adding acid to the entire garden is bad if your other plants prefer neutral soil. Try using an acidic fertilizer around your acid-loving plants instead.
If you aren’t sure which fertilizers will add acid to your soil, ask your local gardening store. Some organic options to consider are:
- Down to Earth Acid Mix
- Espoma Organic Soil Acidifier
- Dr. Earth Acid Lovers
- Bloom City pH Down Liquid Fertilizer
- Fox Farm Cultivation Nation pH Down
11. Use Acidic Liquids
If you need to decrease the alkalinity of the soil, try adding an acidic liquid to the soil. This works best in clay soils or other soil types that retain more moisture; sandy soils will let the liquids run through too quickly.
This is easy to do!
Combine one cup of vinegar (white vinegar) with one gallon of water. Then, apply this around your plants. Vinegar is an easy and inexpensive way to make soil acidic.
Another acidic liquid is lemon juice. It adds acid to the vegetable garden and is an organic choice. All you have to do is add two tablespoons of lemon juice into a gallon of water. Then, pour it around the roots of your plants.
3 Mistakes Not to Make When Adding Acid to Your Soil
1. Amending Your Soil When It’s Not Necessary
Perhaps the biggest mistake you could make is adding acid to your soil when it doesn’t need it. Too much acid is a problem for plants; it will prevent your plants from absorbing the nutrients needed. So, before you start altering the soil pH, take a test to be sure it’s needed for your plants.
2. Adding Blueing Agents
Avoid “blueing agents,” such as aluminum sulfate. They work quickly, but they excessively reduce pH and interfere with the soil’s phosphorus levels. It also leads to toxic levels of aluminum in the soil, so in general, it’s best to avoid these amendments.
The same goes for ferrous sulfate, available at most garden centers, which interferes with phosphorous.
3. Avoid Ammonium Products
Through your research, you may learn that products like ammonium nitrate and ammonium sulfate are effective in making soil more acidic. However, the cost to the planet isn’t worth it.
Ammonia releases a lot of CO2 into the atmosphere each year, so in an effort to take care of our Earth as much as possible, I suggest staying away from these synthetic fertilizers.
If your acid-loving plants need a bit more soil acidity, use these tips to create the perfect pH range. Always remember to perform a soil test before adding any amendments!
