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Using wood ash as a fertilizer is valuable when fertilizing high demand vegetables such as tomatoes, cannabis or pumpkins. However, there are something to watch out for before simply applying to your soil. Let a soil scientist walk you through how to properly apply wood ash to your lawn and garden.

My name is Ashley and I am a soil scientist. I graduated from the University of Saskatchewan College of Agriculture and bio resources. I’ve been working in the field of Agriculture for nearly 10 years now and have been an avid Gardener for much longer. I truly enjoy using my formal education combined with my work experience to give you the best results in the garden. Today we are exploring the use of wood ash as a fertilizer in the garden or for the lawn.

Using wood ash for fertilizer in the garden is a new up-and-coming way of fertilizing. While there are benefits to using wood ash. There are also some cautions you should be aware of before deciding to use this organic fertilizer. Undoubtedly one benefit is the cost of wood ash as it is readily available for anyone, anywhere because it is a byproduct of a fireplace or a wood-burning stove.

Why Use Wood Ash In The Garden

It seems wasteful to throw wood ash in the landfill. Especially when we know that there are benefits to using it in our garden. In this article we will explore the crops that benefit the most from wood ash such as tomatoes, peppers, and other heavy feeders.

Then we’ll get into how to use wood ash on the lawn. Of course we’ll talk about the issues that may arise with using wood ash as a fertilizer. But will also talk about the benefits and what we will see if we decide to use fireplace ashes as a garden fertilizer.

What Is Wood Ash?

In order to understand how to use wood ash as a fertilizer for the garden. We need to understand exactly what wood ash is. If you follow me on YouTube you will already know my thoughts on using charcoal as a soil amendment. Wood ash is different than charcoal in more ways than one. They act very differently in the soil profile and there’s very little similarities between the two products.

Charcoal vs. Wood Ash

Charcoal for example is the black nuggets of wood that we can incorporate into potting soil. This is commonly used in tropical plant mixes as a way to harness nutrients and reduce smell. For more on that please check out my charcoal video on how to use this properly in a garden or houseplant setting.

Wood ash on the other hand is the white ash that we find in the bottom of our fire place after we’ve had a fire. Wood ash is similar to dust and it should melt away in your hands. There should be little to no chunks involved when we are using a true wood ash product. You can also use the byproduct from pellet furnaces, wood-burning stoves, outdoor fire pits etc.  One thing to keep in mind is that we should not use wood ash in the garden that is a by-product of treated wood burning. If the wood has been used in construction and is discolored, such as green or stained brown, this should be excluded from a possible fertilizer Amendment.

Different Types Of Wood Ash

There are different types of wood ash each one giving us a different nutrient profile. We already know about the treated wood ash and how this should not be used in any fertilizer setting. However when we look at hardwood vs. softwood We can start seeing differences in the nutrient profile. Hardwoods typically have higher levels of both macro and micronutrients. This makes it a superior fertilizer for the garden or lawn.

Using Hardwood For Wood Ash Fertilizer

This also makes hardwood wood ash a fertilizer that can be over applied when we’re talking about micronutrients.  Keep this in mind when you are choosing how much and where to apply your wood ash in the garden. Some examples of hardwood include Alder, Aspen, Bolsa, Beech, Hickory, Poplar, teak, Walnut and the list goes on.

Using Softwood For Wood Ash Fertilizer

Softwoods typically have a less dense nutrient profile both on the macro and micro side. This ultimately lessens the chances of over-fertilization. Examples of softwood are Douglas fir, Juniper, Magnolia, Pine, redwood, spruce and many more. 

Using Stove Pellets For Wood Ash Fertilizer

When looking to use a pellet wood ash by product be sure to look at the company’s procedure for producing the pellet. Typically speaking they are untreated and they can be a combination of both softwood and hardwood. This can make it more difficult to determine what the macronutrient and micronutrient profile of the wood ash. However, I will be giving you a catch-all recipe to applying this on your soil.

Main Nutrients In Wood Ash

The main components of wood ash consists of 0 – 1 – 3 (N – P – K ) along with calcium  and magnesium. There are also 14 other essential nutrients that the soil usually supplies the tree to grow. Once the wood ash is burnt down these components that were once in the soil and were translocated into the tree are now available for our fertilizer.  

Why Phosphorus Is Important To Plant Growth

Phosphorus the middle number is incredibly important for a living plant cell. It is involved in key plant functions that include energy transfer, photosynthesis, transformation of sugars and starches, genetic characteristics from one generation to the next, and overall nutrient movement within the plant. Without phosphorus, plants would not be able to survive.

Phosphorus is important because it actually is a main driver behind root development. If you are noticing a plant is struggling after a bug attack or disease, addition of phosphorus to the soil profile will help that plant recover. This is done through nurturing more root growth. One of the best times to apply a phosphorus fertilizer is after a storm that may have caused turbulence both above and below ground. 

Why Potassium Is Important To Plant Growth

Potassium is important to plants because it is involved in enzyme reactions throughout the plant system. Potassium is the last number in the 3 digit text. Often potassium is referred to as potash.. Potash is not the nutrient name it is the name of the rock potassium is pulled from. 

Why Calcium Is Important To Plant Growth

Calcium in plants is important for structural support in the cell walls. Calcium serves as a messenger for the plant when it is physically or biochemically stressed. If you watched my YouTube video on the Tel Aviv plant study. When they researched the response a plant had to stress by measuring the calcium distribution within the plant biomass. You will know what I am talking about. If you haven’t seen that be sure to check it out. It is a fun study.

Calcium in the soil however is rarely deficient. Most calcium deficiency signs that show up in a plant is a result of improper pH. I commonly talk about pH of the soil and how it affects the plant because it is important to understand more fertilizer will not fix the issue. If you add calcium in the form of egg shells, a fertilizer, or wood ash and you have not changed the pH you will not change the uptake the plant has access to.  Calcium is thought by many to be able to stop the splitting of things like tomatoes as they flush out. But again this is a little bit of a common misconception. 

Using Wood Ash In Potting Soil

The exception to this would be soilless potting medium. For example a peat moss or coconut coir based potting soil would be deficient in calcium in some cases. Especially if it is being reused. This is where wood ash or a calcium supplement may be beneficial. But again you’re going to want to know what your pH is before determining if it is a calcium deficiency or simply a nutrient availability issue. If you are looking to reuse potting soil check out this blog post

Why Phosphorus Is Important To Plant Growth

Magnesium in plants is essential to the chlorophyll molecule. Chlorophyll is the factory where photosynthesis takes place. If magnesium is deficient it can result in shortages of chlorophyll and poor or stunted plant growth. Magnesium is also important in complex enzyme reactions that build, modify, or break down compounds within a plant’s metabolism. 

Magnesium is another nutrient that is generally high in soil concentration throughout North America. Therefore a magnesium deficiency is usually a result of poor soil pH. Again the exception to this rule would be soilless potting mediums.

Common Issues With Using Wood Ash As Fertilizer

Some major alarm bells that go off when I hear about using wood ash in the garden. This is due to the amount of lye and salt within wood ash. Due to the high levels of both these substances wood Ash can become toxic in high levels. 

It is important to never mound or clump wood ash in any area of the swell. The result will be an area where nothing grows. This is due to the lye and salt concentration that will build up in this section of soil.

We will get into the best way to reduce the amount of the salt and lye substances within the wood ash mixture a little bit later.

Seed Starting And Wood Ash

Starting seeds after a wood ash application is less than ideal. Wood ash will cause an area of inhibition where seeds will not germinate. Ensure that you do not apply wood ash before you have started your seedlings. Transplanting into a recently fertilized area is okay as long as the transplants are full grown plants. I typically like to wait until the plants have at least five or more true leaves before applying wood ash as a fertilizer after seeding.

What Crops Benefit Most From Wood Ash

Let’s look at what vegetables or crops will benefit the most from the use of wood ash as a fertilizer. Because we know that wood ash has a high concentration of some macro and micronutrients it would make sense that we would choose heavy feeders as a candidate for a wood ash fertilization. 

Tomatoes And Wood Ash

Tomatoes are commonly known to have calcium or magnesium needs that are very high. This is why a soil supplemented with wood ash would benefit a tomato plant. In order to stop splitting of the fruit or weak plants as the growing season progresses try wood ash mixed into the soil or compost to ensure better results.

Using wood ash versus egg shells will result in better nutrient uptake. The reason for this is because of the form that these nutrients are in. When in a wood ash is in a farther decomposed state than a whole eggshell. There difference maybe if you were to crush your egg shells before applying it to the soil. The key is increasing the surface area for microbes to interact with the calcium forms in each product.

Cannabis And Wood Ash

Again cannabis would be a crop that would benefit from the use of wood ash. This is because most cannabis growers typically grow in soilless mediums.  Anyone growing in a peat moss based soil would benefit from the utilization of wood ash. The reason being that calcium and magnesium or in some short supply when looking at soiless mediums.

Using Wood Ash On Lawn

Using wood ash for your lawn is also hugely beneficial. There is no nitrogen in the wood ash therefore you will also want to supplement with another fertilizer.  However, you will see results because of the high levels of both phosphorus and potassium. Both of these nutrients are integral to ensuring a lush green lawn.

Using Wood Ash On The Whole Garden

Using it in the garden as a whole is also acceptable. One thing to note is you should not use this when you are starting seeds as I mentioned Above.

Application Rate Of Wood Ash In The Garden 

The application rate for wood ash in the garden would be around 10 lbs per thousand square feet to be on the safe side. This equates to approximately half a 5 gallon bucket of wood ash.  Again when applying this to the Garden you want to ensure that there are no clumps and that everything is evenly dusted across the soil surface area.

I will repeat this mostly because I want to ensure everyone understands do not apply wood ash to an area that you plan to feed or start seeds in.

Application Rate For Wood Ash On The Lawn.

Using wood ash for lawn fertilizer will result in benefits. The application rate for this can be a little bit higher once the lawn has started growing. Using one five gallon pail total per thousand square feet is okay. This will suppress weeds that have not yet germinated while supporting new growth of grass. If you feel as though you have over fertilized, always water.  my favourite saying is when in doubt water it out.

Using Wood Ash To Increase Soil pH

Wood ash is just as effective as a lime for increasing the soil PH. If you have an acidic soil, using wood ash will cause it to become alkaline. This may be beneficial if you are having issues with increasing soil pH. Keep in mind if you’re using this as a pH increase soil amendment you are still running to the risks of the high salt concentration in wood ash. 

However if things such as lime are not working to increase the pH of the soil this can be used as a last-ditch effort.  If you choose to use wood ash as a pH increase, apply the wood ash and then test every month for approximately three months before reapplying.  It may take time for the microbes to break down the wood ash and ultimately alter the pH permanently. You want to avoid an over application at all cost.

Using Wood Ash In Compost

Using wood ash in the compost is arguably the safest. The reason for this is as the compost is “cooking” for lack of a better term. The wood ash concentrations of salt and lye will leach out of the system. This will ensure that when application time comes you are not going to deliver a toxic dose. 

If you choose to use wood ash in the compost all you will simply do is sprinkle a thin layer of wood ash every time you add more compost. This even distribution will allow for proper leaching of the harmful substances.  When it comes up to applying this to the garden you would apply at a regular rate that you would any compost. If you want to use wood ash but you are shy about using it in its purest form then this is the solution for you.

Using Wood Ash As A Herbicide

Using straight wood ash as a herbicide is incredibly effective. For many reasons such as its ability to change the pH of the soil and the naturally occurring toxic levels of salt and why. All you have to do is simply apply straight wood ash in a high quantity over the weed in question.

It is important to note that if you choose to do this it should be in an area that is either cement or brick and is not connected to your garden.  Where the strong concentration of wood ash is applied everything will die.  After this you can reapply as you see fit.

Using Wood Ash As A Pesticide

Wood ash as a pesticide for Slugs and snails is arguably the most effective way to control these pests.  Because it is toxic to the Garden you are going to want to make sure that you apply it as far away from the actual plant itself as possible. This means you may want to Simply outline the garden bed in question.

When you apply this as a pesticide against slugs and snails you will want to lead a relatively thick border around the Garden area.  When they crawl through this they will dry out and die.  they may just avoid it altogether because they can sense it is what ash from a distance.  It is a combination of the high salt concentration and the texture that tends to deter the Slugs and snails.

Summary Of Using Wood Ash In The Garden

When we look at using wood  ash in the garden we can see the ultimate benefits, but also drawbacks of this fertilizer. Wood ash is a byproduct of burning wood products and is the white dust that comes out of the bottom of the pit. We do not want to use wood ash from treated wood. And we want to keep in mind that hardwoods and softwoods contain different levels of macro and micronutrients.

Ultimately the hardwood or softwood nutrient profiles does not affect the application rate.

This is because of the high levels of salt and lye within wood ash. The application rate to be on the safe side is a half of a 5 gallon pail per thousand square feet. When using wood ash on the lawn we can increase this to a full 5 gallon pail per thousand square feet. Using wood ash as a fertilizer will result in an increase of calcium magnesium phosphorus and potassium in the spill profile.

However it’s important to note that calcium and magnesium are typically not in short order when it comes to North American soil and any deficiency is most likely caused by a pH imbalance. The safest way to apply wood ash to the garden is when we mix it into our compost. The compost acts as a buffer throughout allowing the lye and salts to be leached from the wood ash through rain and what . 

Feel free to use what I say and let me know what the results are. If you have used with Ash previously please let me know in the comments down below. For more on what I should be sure to check out my YouTube video where we explore the science behind wood ash a little bit deeper.

Wood Ash In The Garden
Wood Ash In The Garden
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