To be successful at gardening or any type of landscaping, you need to monitor soil pH. Start with a baseline test using a digital soil pH meter like the one above, and then you can choose plants to fit that pH range or adjust the pH to what you want to plant. This article will be about how to make soil acidic.
In general, most soil has a pH value of 3.5 to 10. The soil tends to be more acidic in dry areas, in the 6.5 – 9 pH range. Sites that get more rain will have more alkaline soil in the 5-7 pH range.
You’ll want to make the soil acidic if you have alkaline or neutral pH and desire to grow plants that need a more acidic pH (ericaceous).
Before we get into the steps required, let’s go over some reasons you would want to make the soil acidic.
Reasons You Might Want Soil More Acidic
Here are a couple of reasons you might want to change your soil to a more acidic pH level.
Acidic Soil Turns Pink Hydrangeas Blue
The exciting thing about hydrangeas is that the acidity in the soil will change the color of the flowers.
It is done by altering the soil pH from 5.2 to 5.5. This is the pH where blue flowers will show. You will also want to add some aluminum to the soil. This is done by adding aluminum sulfate to the soil around the plant.
The recommended amount is one tablespoon of aluminum sulfate for each gallon of water during the growing season. But, before doing so, make sure to give the plants a good watering and be careful with how you apply it, as the roots can be burned if too much is used.
So if you plant so new flowers in the area, and want to change the color so they match better, you can simply change the soil pH.
The bad part about this is that you’ll have to stay on top of the pH each year until it holds a steady acidic pH.
Another thing that will help produce an excellent blue color is using a high potassium fertilizer and low phosphorus. A ratio of 25/5/30 is ideal.
Wait, What About Ammonia Sulfate?
Gardeners often get aluminum sulfate and ammonia sulfate mixed up (easy to do). Now, let’s talk about ammonium sulfate, the nitrogen-packed powerhouse.
It encourages lush growth, vibrant green foliage, and overall plant happiness. This wonder-worker also adds a touch of acidity to the soil, making it a versatile option for many flowers. Just remember, moderation is key! Overdoing it with nitrogen might stress your plants out, and it is considered hazardous (Chemically, when aluminum sulfate is mixed with water, it transforms into corrosive sulfuric acid) so follow safety precautions.
So, there you have it! Aluminum sulfate for acidity and blue hydrangea magic, and ammonium sulfate for a nitrogen boost and happy, thriving flowers.
Another Option: Ferrous Sulfate
Consider using ferrous sulfate as an alternative. Similar to aluminum sulfate, it has comparable acidifying properties and is used as a soil amendment to lower the pH of excessively alkaline soil, allowing plants to access the soil’s nutrients more effectively.
It is usually utilized to remedy yellowing plant leaves caused by iron deficiency, making it an excellent choice for rhododendrons, camellias, or azaleas that appear yellow and droopy. Although most garden centers carry ferrous sulfate, it can be expensive since you need eight times the amount compared to sulfur (more about sulfur below).
Grow Plants That Require Acidic Soil
Some plants like the blueberries above require an acidic soil So if you have a soil pH of 5.5-10, you’ll want to lower it. Blueberries need a pH of 4.3 to 5.5.
You just want to be careful not to lower the pH too much. Slow, steady changes are better than too much, too fast.
When you get to lower pH soil ranges, bacteria stop breaking down organic material. This means fewer nutrients are available for the plants.
Nutrients are also known to be more soluble and easier to wash away at the pH ranges of 3-5.
Alkaline Soil Is Causing Plants Nutrient Deficiencies
If you have naturally alkaline soil and try to grow acidic-loving plants, they may suffer nutrient deficiencies.
When the soil is alkaline, manganese, phosphorus, and iron are not as available.
A soil test can confirm a high alkaline soil if you see this happening. You will want the soil to get to around 6.5-7 for an excellent general garden pH (webpage). This pH range will allow the best soil pH for most plants to do well as bacteria and nutrients are plentiful in this pH range.
Once the overall plot has been corrected, you can section off an area for more acidic soil if needed.
Ways to Make Soil Acidic
The part you have been waiting for. Here are some natural soil amendments to lower the pH in your garden soil.
Methods for How to Make Soil Acidic
Adding compost to your slow is a great way to add organic material that bacteria thrive on. Helping to balance soil pH with a nice and slow process.
Use it as a topdressing and work it with a broad fork into the soil.
Add Leaf Compost
Composting leaves and adding them to the soil will slowly lower soil pH. Oak leaves work great for this (not to mention, if you have a large Oak tree, there will be plenty of them). This will add nutrients to the soil and help retain water.
Add Elemental Sulfur
Sulfur is a way to combat soil with very high alkalinity. It will slowly lower the pH of the soil. But, for sulfur to work, you need to adjust the amounts used to the correct type of soil. Sandy soil or those with high amounts of organic matter will require more sulfur than clay. Spring application of sulfur is best (PDF). Note: Sulfur works slowly, so it’s best to apply one year before planting.
Add Pine Needles
Adding pine needles to mulch or mixing it into the soil will slowly acidify the soil. You can also add pine needles to compost for the same effect.
Use an Acid Based Compost Tea
Compost tea that is made with ericaceous materials (acid pH) will help lower the soil pH and add nutrients.
Add Acid to Water With Lemons/Lime/Vinegar
A simple way to lower the alkaline soil is to add acidic liquids to your water. You can use items such as limes, lemons, or vinegar. But make sure you don’t overdo it.
With vinegar, you should only use one cup to one gallon of water.
Add Canadian Sphagnum Peat Moss
Adding a layer of Canadian sphagnum peat moss will help lower soil pH since it has a 3 – 4.5 pH. But ensure that the peat moss you use is Canadian. Other garden center peat moss may be only slightly acidic and not have much of an effect.
Types of Plants That Grow in Alkaline Soil
Suppose you have alkaline soil and don’t want to make your soil more acidic; these alkaline plants thrive in higher pH soil.
Alkaline Soil Trees
- Montezuma pine
- Field Maple
- Cotoneaster frigida
- Sorbus alnifolia
- Holm oak
- Strawberry tree
Alkaline Soil Shrubs
- Viburnum opulus
- Santolina chamaecyparissus
Alkaline Soil Vegetables
Many vegetables prefer alkaline soil; Asparagus is one of them.
- Pole beans
Alkaline Soil Herbs & Flowers
- California poppies
- Wild marjoram
- Lily of the Valley
- Viper’s Bugloss
- Trifolium (clovers)
Plants That Thrive in Acidic Soil
If you’re starting with acidic soil or will use the steps in this article to make your soil more acidic, the following plants will work well.
Acidic Soil Trees
- Willow oak
- Pin oak
Acidic Soil Shrubs
Acidic Soil Flowers
- Japanese iris
Pretty much any fern will do well with acidic soil and some shade.
Remember to make small and slow changes. Soil pH doesn’t change overnight and you want to give it the correct amount of time before planting.
Also, don’t skip the part about measuring your pH. It’s important to know what kind of soil you have to make the most out of it. Use a quality pH scale, and growing plants will be more successful. Healthy, thriving plants are much more satisfying than withering, sickly-looking plants.
Finally, adding compost and organic material to your soil is always a good idea. And a good practice to learn. So, if you need to lower the soil pH for blueberries, now is an excellent time to start learning how to adjust pH and add organic material to the soil.
Your future garden will thank you!
Frequently Asked Questions
Can you check soil pH without a meter?
Yes, you can check your soil pH without a digital meter. Use a container to put a small amount of soil in it. Then, test with vinegar and bicarbonate soda. You will look for a reaction and see which one causes it bubbles to appear. Here is a video that demonstates the process:
How do conifers make the soil they grow in too acidic for other plants to grow?
Most people think this is because the pine needles are 3.2 to 3.8 pH. But that is for fresh pine needles. Needles that are dead and on the ground will break down and become more alkaline. Most often, the problem is that confier roots are numerous and shallow. Making it difficult for other plants to establish their roots.
Simply place a small amount of soil from your garden in a jar of vinegar.
If it froths up, the soil is alkaline in nature. If it does not, this may not be the problem where you live.
You may also be able to get some clues about soil pH by looking at the plants already in your garden, and in the surrounding area.
If there are plenty of plants that like alkaline conditions, this will give you a clearer idea of what else will do well in your garden.
If you do have alkaline soil, especially if it is not extremely so, it is a good idea to consider working with what you have.
Consider fitting the plants to place, rather than trying to alter the place to suit different plants. Rather than amending the soil, choose plants that will naturally tolerate or even thrive in the conditions where you live.
Soil pH PDF: nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052208.pdf
Soil pH PDF: qld.gov.au/environment/land/management/soil/soil-properties/ph-levels
Change color of hydrangeas: ndsu.edu/pubweb/chiwonlee/plsc211/student%20papers/articles09/haylee%20a%20wax/pH%20affects%20on%20hydrangea%20-hw.html
Blueberry pH: blog-yard-garden-news.extension.umn.edu/2020/01/smart-gardening-2020-how-to-prepare_31.html
Pine Needle pH and Growing Myth: extension.oregonstate.edu/news/myth-vs-reality-whats-truth-behind-some-common-gardening-practices
Canadian Sphagnum Peat Moss pH: hortnews.extension.iastate.edu/2016/02-12/soilpH.htm
Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.