Are Fire Pit Ashes Good for Your Garden? Does It Make a Good Fertilizer?

a bucket of burnt wood ashes being used in a garden

Fire pits are a fun spot to hang out with friends and family. However, fire pits that burn wood as their fuel produce a lot of ashes. Many people use these ashes in their gardens, but are they good fertilizers?

Fire pit ashes can be beneficial for your garden if it has acidic soil. If your soil is alkaline, then fire pit ashes could harm your plants. Fire ash contains lime, potassium, and many other nutrients. However, it also contains heavy metals that can hinder plant growth.

You need to understand the benefits and drawbacks of using ashes in your garden before you make a decision. Otherwise, you could put at risk the health of your plants, trees, and shrubs.

Why Fire Pit Ashes Can Be a Good Fertilizer

The ashes produced by the wood burned in a fire pit can be highly beneficial for your garden. These ashes contain potassium and lime, which are really helpful in promoting healthy growth in plants.

Fire pit ashes also contain other nutrients in trace quantities, such as sodium, magnesium, phosphorus, iron, boron, and zinc. These are important for growing certain flowers, vegetables, and fruits.

Besides all this, the pH of your garden soil can be altered using fire pit ashes. Ashes have a pH of between 10 and 12, which means they’re highly alkaline. Adding fire pit ashes to your soil can help you balance highly acidic soil and bring it to the optimal level.

Keep in mind that fire pit ashes don’t have nitrogen—a crucial nutrient for plants that you’ll find in any fertilizer. This means that fire pit ash won’t replace general fertilizers.

Some of the plants that will benefit from fire pit ashes are:

  • Wild strawberry
  • Garden-ball thistle
  • Ivy
  • Several maple species
  • Garden Silver Root

I should note that the benefits of fire pit ash are only present if they’re made of burnt wood. If you burned briquettes or coal in your last fire pit, then those ashes will do more harm than good to your garden.

close up of a hand spreading fire pit ashes in their garden

Why Fire Pit Ashes Be Harmful to Your Garden

However, using fire pit ashes in your garden isn’t always a suitable option.

As already mentioned, adding fire pit ashes to your garden soil can increase its pH level. While this can be helpful, it can also cause harm to your garden.

If the pH level of your garden soil is too alkaline, it can negatively impact plant growth. This is especially true if your plants prefer acidic or neutral soil. 

Besides this, fire pit ashes can contain heavy metals such as copper, lead, arsenic, and chromium.

Excessive concentrations of these metals in your soil can be very problematic. They stop microbes and enzymes in the soil from doing their job, which is necessary for plant growth. These heavy metals can also latch onto plants that produce fruits and vegetables and end up in our bodies, which is a health hazard.

How Much Fire Pit Ash Should You Add o Your Soil

Before making the decision to add ash to your garden, you need to test the PH and nutrient concentration of your garden soil.

You should also check the soil parameters for your individual plants. In fact, the wisest thing is to only fertilize with ash if you have plants that thrive with high lime content or peat-based soils. Even then, as with every other fertilizer, going overboard can harm your plants. 

If your garden soil is only mildly acidic and you add heaps of fire pit ashes to it, the soil will become barren, and plant growth will stop entirely. If you add much more nutrients than your plants need, it can cause nutrient toxicity. The truth is that most soil has enough calcium to get around without the need for fire pit ash.

Dumping excessive amounts of fire pit ashes in your garden will also increase the heavy metal concentration in your soil and deteriorate the surface water quality.

Now that I’ve made clear when you should and shouldn’t add ash to your soil, let’s get down to the measurements. If you have heavily acidic soil, use between 200 and 400 grams of ash for every square meter (between 0.6 and 1.3 ounces per square foot). If your soil is only mildly acidic, then use less than 200 grams.

Ideally, you should spread ash every 3 or 4 years, but his period can vary depending on the acidity of your plants and how much ash you spread.

How to Add Fire Pit Ashes to Your Garden

After you’ve conducted a soil test, you can’t simply fish the ashes out of your fire pit bowl and spread them everywhere in your garden. There is a procedure you need to follow to ensure maximum effectiveness.

The beginning of spring is the best time to add ashes to the garden, right around the time you would add manure. This is because the ashes need time to have an effect on the soil.

Make sure to spread ashes on a day without much wind and wear gloves to protect your hands.

  1. Wait until the ashes have cooled completely before adding the ashes. If the ashes are still hot after a long time, put them in a container with a large surface area to help speed up the cooling process. 
  2. Sift the ashes using a fine mesh sieve. This way, you can leave out any large chunks of half-burnt wood or coal, which can harm the roots of your plants.
  3. Spread a layer of ash over your soil. You can use a rake to spread them more evenly. Try not to lift more than six inches of soil with the rake.
  4. Don’t combine ashes with other fertilizers. Although it’s tempting to take the chance and add manure or artificial fertilizer, chemicals in these substances will mix with ash to create ammonia and make calcium less accessible to plants.
  5. Wait at least 14 days before planting anything. That’s it! You just have to give your soil a bit of time.

Other Ways To Utilize Your Fire Pit Ashes 

Sometimes you may be unable to use your fire pit ashes directly in your garden, or maybe you have more ashes than you can add to your soil without it being excessive. If that’s your case, here are a few other things you can do to utilize these ashes:

  • Put a small amount of ashes in your home compost along with your other biodegradable waste.
  • Mix the ash with water to make a cleaning paste. Ash is a mild abrasive, and you can use this mix to clean a variety of surfaces.
  • Place a ring of ash around your plants to keep snails and slugs at bay. These pests can do significant damage to your plants.
  • Ash is an excellent absorbent. It can be used to absorb any foul smells in spaces with insufficient ventilation, such as a garage or a storage shed.


Fire pit ashes can be used in gardens, provided you don’t overdo it. It’s best to err on the side of caution and get your soil tested before proceeding.

It’s best to think of ashes as a way to help specific plants flourish. If you have lime-loving plants that thrive in alkaline soils, then you can be more generous. If you plan to spread ashes as a general fertilizer, then be cautious. Use a little the first time and see how your plants react.

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