How To Make Potting Soil More Acidic

It can be a problem.

Your potting soil has turned too alkaline, causing plants to suffer. Or you need to grow plants that prefer acidic potting soil.

You can make potting soil more acidic using materials such as elemental sulfur, ammonium sulfate, fresh coffee grounds, peat moss, compost, or mulch. You can use a store-bought organic acidifier that contains a mix of some of these. You can test your soil pH every few weeks to check for improvement.

In this post, I’ll show you how to use some of these organic materials to increase the pH of your potting soil so your plants can grow better and get the desired gardening results.

Shall we begin?

Good potting soil has a balance of nutrients so it is slightly acidic in the 6.0-7.0 that most plants prefer. But some plants like blueberries like more acidic soil. The best way to know the pH of your soil is with a pH meter. You can find the best pH meters on Amazon.com.

1. Lower pH In Soil With Sulfur

Elemental Sulfur is one means to lower the pH of your soil and create a more acidic environment for your plants. You should be able to purchase the Sulfur from most local nurseries or garden centers. If you cannot fins elemental Sulfur, you can substitute with Aluminum Sulphate, but you would need to use 6-times the amount.

The only downside to using Sulfur is that Sulfur quantities are in tenths of a pound per 10-square feet of soil. The best way to get around doing too much math to find out the volume of soil in your container is to mix a batch of adjusted soil and use this as your potting mix.

Elemental sulfur but it takes months to breakdown. And once coffee has had water to it, it is no longer acidic. – Cashelda

0.1-pound of elemental Sulfur per 10-square feet of soil will increase the acidity level by 0.5pH. If you are using Aluminum Sulphate, you need to increase the mix to 0.6-pounds per 10-square feet of soil.

Sulfur takes a long time to acidify the soil, so do not add too much Sulfur. Check the pH level every 4 to 6-months and only then add more Sulfur.

Does Peat Moss Acidify Soil?

Peat moss does acidify the soil, but it will take a long time as it’s a slow process. Depending on the particular size of the plant pot, you can put 2-3 inches of peat moss on the top of the soil and mix it into the soil.

Monitor the pH level over the next 3 or four weeks to check the pH range. This amount of peat moss will slowly release acidity into the soil and should not need to be replenished for 6-months to a year.

Do Used Coffee Grounds Make The Soil More Acidic?

Used coffee grounds don’t make the soil more acidic because they have a pH of around 6.5, making them closer to neutral. But they do add good amounts of nitrogen to the soil.

Leftover coffee would make a better soil acidifier than the used grounds themselves. You can dilute leftover coffee in water and use it to water your plants in a 50:50 solution. There is no documented amount that will change the soil by a specific pH, so with this method, you will need to wing it and test your soil pH once a week or so. 

Coffee grounds are really only effective if you DON’T drink the coffee, so unused coffee grounds. – Gabriel

The acidity in the coffee is mild enough that it will not make dramatic changes to the soil pH, so this method is suitable if you only need to make a small adjustment in the acidity of the potting soil.

However, fresh coffee grounds will make the soil acidic, but who wants to waste freshly ground coffee?

Can You Use A Nitrogen-Based Acidic Fertilizer?

You can use a nitrogen-based acidic fertilizer to lower the pH of the potting soil. Nitrogen-based fertilizers that have high ammonium content will increase the soil acidity faster and by a larger amount.

Nitrogen is a key ingredient needed for your plant’s health, and certain types of nitrogen-based fertilizer can be used to increase the acidity of the potting soil.

Nitrate-based nitrogen fertilizers will also acidify the soil to a lesser degree and over a longer time frame. If you want to use a nitrogen-based acidic fertilizer, it would be best to consult your local garden center for the best formula to use.

Best way of changing soil pH is to get soil tested (county extension agency in USA) and follow recommendations for amendments for type of plant(s) you want to grow. – Steve

Will Compost Help Lower The Soil pH?

Compost can help bring the soil pH closer to neutral because it tends to have the right balance of organic matter. Materials such as pine needles or pomace are acidic but break down in the compost and lose acidity.

It is a common garden principle that natural compost of various forms will affect the pH value of the soil. Let’s check out some of the more common ones that people promote as changing the soil pH.

• Oak or pine leaf mold. Oak leaves and pine needles are acidic when they are fresh. When they begin to decompose, the acidity is broken down in the process, and they become close to neutral in pH value.
• Pine needles. Fresh pine needles turned into the soil can make the soil slightly more acidic, but the amount of acidity change is not significant.
• Well-rotted hardwood sawdust. Hardwoods are acidic, and sawdust from these woods, even when well-rotted, will make the soil slightly more acidic, so only use on plants that prefer acidic soils. If it is not well-rotted, the sawdust can absorb much of the nitrogen in the soil while it decomposes and prevent plant growth.
• Pomace (dried pulp from cider mills). Pomace is acidic and can be used to make the soil more acidic. Add pomace carefully and conservatively and test the pH of the soil regularly to test for correct pH.

Will Mulch Help Lower The Soil pH?

Mulch can help lower the soil pH if you bury acidic materials such as pine needles, pomace, and pine leaf mold into the potting soil. Mulch will not help if you place these materials on top of the potting soil, as they will break down and become neutral.

Mulch is used as effective moisture and temperature control for soil and even as a weed suppressant, but can mulch materials affect soil pH?

• Oak or pine leaf mold. As long as the leaves are well dried, they will not affect the soil pH in any significant way to adjust the pH value.
• Pine needles. Pine needles used as mulch on top of the soil will not alter the soil pH in any significant way and therefore would not be an effective method of adjusting pH.

Pine bark is a good acidifier and you can buy soil especially for acid loving plants. – Roy

• Well-rotted hardwood sawdust. If the sawdust is well-rotted, it can be used as mulch and will not make the soil acidic. If it is not well-rotted, it could absorb much of the nitrogen in the soil and prevent plant growth.
• Pomace (dried pulp from cider mills). Pomace can be used as mulch, and it will make the soil slightly more acidic.

Does Garden Lime Make Soil More Acidic?

Lime does not make the soil more acidic; it actually has the reverse effect and reduces the soil acidity, making it more alkaline. You should use lime conservatively since too much lime can burn the roots of your plants, doing more harm than good.

Lime is best added to soil and then left to break down for about 3 weeks before planting in the soil. 

Will Baking Soda Lower Soil Ph?

Baking powder is an alkaline substance, and adding it to the soil will raise the pH level, thereby increasing the alkalinity of the soil.

Baking soda is gentler than lime and works faster, reducing acidity in the space of 24-hours in some cases.

Mix 1-tablespoon of baking soda in 1-gallon of water. Water the plant pot every second day with this mixture and gently turn the soil’s surface over. Test the pH every second day until the desired pH has been achieved, then stop using the solution.