Does Wood Ash Fertilizer Lower Soil pH?

Wood ash fertilizer is a popular choice for organic, homemade fertilizer. Wood ash is a cost-effective and additive-free nutrient source that provides an excellent potassium boost to plants that thrive in alkaline soil.

Wood ash fertilizer does not lower soil pH. Because of its high calcium content, wood ash increases the pH of the soil. Wood ash diminishes the acidity and alkalizes the soil, creating a prime environment for alkaline-friendly plants. 

The rest of this article will explain how wood ash increases soil’s pH level and what type of plants thrive in an alkaline environment. I will also share some ways to lower your soil’s pH level with synthetic fertilizers. 

The High Potassium Content Increases Soil Alkalinity

Wood ash is a healthy supply of potassium, lime, and calcium. Calcium is known to increase soil pH. The calcium in wood ash is abundant and reduces acidity in the soil. When the acidity decreases, the pH level of the soil increases. 

The high potassium content is usually the biggest draw for using wood ash in your garden. Potassium is an excellent nutrient for increasing the mobility of water and nutrients and supporting successful water absorption. 

If your plants would benefit from some extra potassium, be sure to do your research on their preferred soil pH level before applying. Some plants thrive in an alkalized, high pH environment, while others rely on highly acidic, low pH soil to grow successfully. 

You should never apply wood ash fertilizer to plants that need acidic soil, as the sudden increase in pH level can be detrimental to their growth.

How to Use Ash From Wood Fires to Modify Your Soil

Using wood ash in your home garden to modify soil pH is a simple task and, when done correctly, can effectively improve your soil and plant growth. 

To apply wood ash to your garden, you will need to:

  1. Remove ash from the fireplace and sort through it to remove unnecessary debris.
  2. Spread the ash in a thin layer over the soil and around the base of your plants.
  3. Use a rake to combine the ash with the soil and prevent unwanted spreading due to wind.

It will be best if you should only use wood ash in your garden after conducting a soil test and determining your soil’s nutrient needs. 

Additionally, it is best to wear a face covering when applying the wood ash— so as not to inhale any of the ash. If the wind picks up unexpectedly, ash can unpleasantly blow directly at you.

How Much Should You Put in the Soil?

You should apply wood ash to the soil in small amounts, never amounting to more than the soil test indicates is necessary. As a rule of thumb, the University of Wisconsin-Madison recommends you stick to 15-20 pounds or less per 1,000 square feet of garden space. 

You shouldn’t need more than a thin layer over the soil or at the base of your plants to get the job done. Using too much wood ash can harm your plants and cause “fertilizer burn”—leaving you worse off than not fertilizing.

Plants That Thrive In Alkaline Soil

While it is essential to remember that some plants do not do well in a high pH environment, it’s also beneficial to understand that many plants prefer and thrive in alkaline soil. These plants come in all varieties; vegetables, fruits, flowers, trees, herbs, bushes, and more!

Some of the most commonly known plants that require a high pH soil level are:

  • Broccoli
  • Garlic
  • Lavender
  • Pomegranate
  • Aloe vera 

You can read more about the types of plants that thrive in alkaline soil and their beneficial uses for wood ash fertilizer in my other article: Fertilizer vs. Wood Ash: 7 Differences

When Is It Harmful to Use Wood Ash in the Garden?

If, after conducting your soil test, you determine that the pH level of your soil is too high, you should not apply any wood ash. Wood ash applied to high pH soil will only cause it to rise even further. You’ll need something that will increase the acidity of your soil, causing the pH level to drop. 

Before using the ash, you should know the exact nature of the burned materials. Burning harmful materials like plastic, newspaper, or paper plates will create ash that can be more harmful than helpful to your soil. If you plan to fertilize with wood ash, use only untreated wood for the best results.

There are organic, natural approaches, as well as synthetic fertilizers, that can effectively lower your soil pH. 

Natural and Organic Remedies to Acidify Your Soil

There are several ways you can lower the pH of your soil using organic, natural remedies. When aiming for a low pH, it is often best to stick to the organic route and avoid synthetic fertilizers, as these options can sometimes have the opposite effect as the salts in them increase your soil’s pH.  

Here are a few of the best organic options for lowering soil pH:

Organic Urea Fertilizer

Urea fertilizer is composed of animal or human urine, and people sometimes use it to increase the soil’s acidity. While synthetic versions of this fertilizer are more common, you can make it organically by combining the urine with compost and using that mixture to fertilize your soil.

Usually, using urea fertilizer directly on your soil will have too strong a reaction, so mixing it with compost is recommended. 

Peat Moss

Not only is peat moss great for increasing soil acidity, but it’s also a fantastic tool for helping the soil retain essential nutrients.

With that in mind, if your soil is suffering from extremely high pH levels and needs a quick fix, peat moss may not be your best choice, as it tends to work more slowly than other options.

Organic Compost

Organic compost is naturally very acidic and, when applied or mixed with soil, will increase the pH level. Over time, as the compost continues to decompose, that acidity will decrease, so you will need to continuously monitor the pH levels in your garden to ensure it maintains a healthy acidity level. 

Cottonseed Meal

Cottonseed meal is an excellent alternative to synthetic fertilizers while maintaining the same “bagged and ready to go” convenience!

Cottonseed meal increases iron and magnesium in the soil while simultaneously lowering the pH level. Additionally, adding some cottonseed meal to your garden’s mulch during the cold months can provide extra nutritional support!

Synthetic Fertilizers for Lowering Soil pH

If organic fertilizers are not an option for you, many synthetic fertilizers will work well to lower your soil’s pH and make your plants flourish again. 

While effective, it is essential to consider the potential for chemical run-off when using synthetic fertilizers. Make sure that any chemical additives that may run away with rainfall and drainage will not end up in water supplies or environmentally damaging locations. 

Here are a few great options for synthetically fertilizing to lower soil pH:

Elemental Sulfur

Sulfur is commonly used in lawns, commercial landscaping, and agriculture to promote leafy, green growth and flourishing foliage. Many options are available for purchase, some with added nutrients for extra nutritional support.

Iron Sulfate

In powder or granular form, iron sulfate is readily available and effective for lowering soil pH. This product supports the plant’s roots, allowing it to absorb the iron nutrients necessary to grow freely. 

Aluminum Sulfate

The most popular choice for lowering soil pH, aluminum sulfate is relatively cost-effective and works quickly. This product adds nitrogen to the soil, rapidly increasing the acidity of the earth. It is often available in granular form, which can be spread on the soil and then activated with water

Ammonium Sulfate

Ammonium sulfate is a synthetic fertilizer that releases nitrogen and sulfur compounds into the soil, increasing the acidity of the soil. While not quite as potent as aluminum sulfate, ammonium sulfate is still a practical choice. 

Urea Fertilizer

Urea, both natural and synthetic, increases soil acidity significantly and creates an environment of low pH levels, working its way into the soil for 2-3 weeks and having lasting effects for weeks or even months.

Ammonium Nitrate

Ammonium nitrate is potent and can rapidly increase the pH level of your soil. When using this product, it is essential to keep a close eye on it, testing the soil and ensuring you have not overused the product. Overuse can lead to “burning” and harm the plant’s health. 

Whether you choose an organic or a synthetic fertilizer method, the end goal is a healthy, balanced pH level that supports the growth of your plants.

Plants That Grow Best in Acidic Soil

Some examples of common plants that thrive in an acidic environment are:

  • Strawberries
  • Azaleas
  • Rhododendrons
  • Blueberries
  • Magnolias

Be sure to test your soil before applying any type of fertilizer, organic or otherwise. Having accurate soil test results allows you to determine the amount and specific type of nutrients needed to improve the quality of your soil

If possible, treat your soil before planting your garden to create an environment suitable for your unique plants from the beginning. It is much easier to maintain a healthy soil pH than to correct one.


Wood ash fertilizers are an excellent resource for increasing pH levels and alkalizing the soil for plants like lavender, pomegranate, and aloe vera to flourish. However, wood ash is not a good choice if you are attempting to lower your soil pH. 

To lower your soil pH, you will need a fertilizer with reasonable amounts of nitrogen or sulfur to increase the acidity, lowering the soil pH. You can do this with both organic and synthetic fertilizers. Some of the most common choices are aluminum sulfate and organic compost.

If you’re interested in learning more, don’t miss my article on methods to reduce soil pH used by farmers: This is How Farmers Reduce Acidity in the Soil

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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