How to make soil more acidic – 7 easy ways to amend your soil's pH

If you're already considering how to make your garden soil more acidic, this is probably because certain plants in your flower beds aren't doing as well as they should. Alternatively it could be that there are new plants you want to try growing that you know need a more acidic soil than you can currently offer them.

All plants need nourishment to thrive. They take some of this from the soil so knowing the make up of your soil (acidic, neutral or alkaline) is crucial to understanding which plants will grow well. If plants fail to thrive and their leaves turn yellow you may need to make a soil amendment to supplement their need for acid.

It might sound technical but cracking soil health is pretty straightforward once you know the basics. There are several ways to make soil more acidic and it's easy with our expert guide. 

How do you work out if you need to make your soil more acidic?

Analyzing soil types is much easier than it sounds. Finding out how to test the pH of soil enables you to determine whether it's acid or alkaline, and can be done with a simple soil test kit, available from Amazon. Soil pH varies from around 3.5 (very acidic) to 8.5 (alkaline). A reading of 7.0 is neutral. A reading of less than 7.0 is considered acidic.

If you discover you have a more neutral or slightly acidic result when you do the test it's good news, as amending the soil to make it more acidic is much easier than if you have a very alkaline soil.

You could also consider growing acid-loving plants in pots, containers or raised garden beds as an easier solution. Amending a small area like this is far easier than altering the pH in a bigger space. Alternatively, you could consider creating a separate area of acidic soil within your garden to accommodate acid-loving plants.

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Get to know the pH of your soil so you can work out what plants will grow best where. This easy-to-use kit contains everything you need to conduct up to 40 tests, plus it offers advice on the pH preference for hundreds of plants, including shrubs, vegetables, trees and flowers. 

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7 simple ways to make your soil more acidic

If you're looking to grow plants that like acidic soil, or your existing plants aren’t flourishing as you'd like, here are the top tips you'll need to make your soil more acidic and help them thrive.

1. Add sulfur to your soil

This is the go-to method when it comes to how to make soil more acidic, especially as it's usually the fastest way to get results. It's a good option as it lasts for years in the soil, where organisms convert it into sulfuric acid, in the process acidifying the soil. 

'Sulfur can be found as elemental sulfur, a yellow powder that can be applied directly to the soil,' says plant expert Diana Cox of thegardeningtalk.com. 'Following the recommended application rate for sulfur is essential, as too much can harm plants. Another way to use sulfur is by incorporating organic matter high in sulfur, such as peat moss or pine straw, into the soil.'

Sulfur won't instantly lower the soil pH, so ideally it should be added in the summer or fall before the following spring planting season. Available at Amazon, it works best if you dig it deep into the soil, but doesn't work if you try to dig it in around existing plants.

2. Use aluminum sulfate

When the results of your pH test show your soil to be more alkaline than your plants like, another option to lower the pH is aluminum sulfate. It's also what you need to use if you want to acidify soil to turn pink hydrangeas blue. It's widely available at any garden center or online at Amazon. 

Mix ¼ oz aluminum sulfate with a gallon of water and soak the soil surrounding your hydrangeas in spring, as soon as the plant begins to grow. Maintain the acidity during the growing season, so reapply in four weeks time, then again in eight weeks.

3. Try ferrous sulfate

Much like aluminum sulfate, ferrous sulfate has a similar acidifying capacity and is used as a soil amendment for lowering the pH of a high alkaline soil so plants can more readily access the soil's nutrients. It typically fixes yellowing plant leaves caused by iron deficiency.

So if your camellias, rhododendrons or azaleas are looking a little yellow and tired an application of iron sulfate should perk them up. Most garden centers stock ferrous sulfate, but as you need eight times as much compared to sulfur, it can work out more expensive.

4. Experiment with vinegar or lemon when watering plants

If you like the idea of natural solutions this easy fix can be used to gently acidify soil around plants. Try watering acid-loving plants in pots, containers or raised garden beds with an acidifying liquid feed. It's particularly good for rhododendrons and azaleas.

Vinegar is a liquid form of acetic acid, so adding it to soil naturally lowers the pH and increases its acidity. The pH of grocery store white vinegar is 2.4, meaning it's highly acidic. Use it in moderation, watering your plants with a mix of 1 cup of vinegar diluted in 1 gallon of water.

Adding diluted lemon juice once a month to the soil also makes it more acidic. It can also help keep neutral soils more friendly for acid-loving plants, including rhododendrons. Add 2 tablespoons of lemon juice to 1 gallon of water and pour directly onto the soil. Be careful as splashing the plant's leaves can burn them.

Talking of watering plants, it is also better to use rainwater rather than tap water, which tends to be alkaline and can actually raise the pH level of soil over time. 'Use a rain barrel or other collection method to retain as much rainwater as possible to use on your plants,' says Drew Swainston, gardens content editor for Homes & Gardens. 

'Acid-loving plants can be watered with tap water, but ensure it is only for a short period of time as possible. Extended use can lead to their leaves starting to turn yellow. The addition of lemon or vinegar to tap water can help to lower the pH of the water.'

5. Use coffee grounds to increase acidity in the soil

Using coffee grounds on plants can be a good option for acid-loving varieties. Coffee grounds are highly acidic, so they will lower the pH of your soil. They are also rich in nutrients, especially nitrogen, as well as traces of potassium and phosphorus. So adding coffee grounds to your garden as a general fertilizer also works well. 

'Coffee grounds have a pH of around 6.5, which makes them an excellent soil amendment for plants that prefer slightly acidic soil,' says horticulturalist Brody Hall of The Indoor Nursery. 'To use coffee grounds to acidify potting soil, it is best to compost or mix it through the soil and let it sit for a week or two. Applying coffee grounds directly to the soil or sprinkling them around the base of plants may attract molds and other pathogens that can affect plant health.'

6. Make an acidic mulch

Although most types of mulch and compost make soil less acidic there are a couple of options you can try that will actually increase soil acidity. Mulching to make soil more acidic is part of a longer term plan though so don't expect to see instant results. 

Try adding mulches of pine needles or oak leaves around acid-loving plants to make sure that the soil remains at the right pH level over time. As these break down, they should slowly acidify the soil. 

If you have conifers in your yard, these can also help to make the soil more acidic once their foliage rots down. 'With conifers, the wood and leaves tend to rot down to compost that is quite acidic,' says John Negus, an expert for Amateur Gardening magazine. 'So if you have hedge plants that have been dropping leaves on the soil, it is likely they will have lowered the pH by some degree over time.'

7. Add compost to your soil

Well-decomposed compost helps lower the pH of garden soil over time. Be sure to include acidic organic matter such as oak leaves, pine needles or coffee grounds to the mix. Simply add the compost and let the earthworms do the rest.