Using Ash in the Garden: Pros and Cons

As a pellet burner, you’ve likely pondered what to do with all the ash left after the heating season. Disposing of it may feel wrong, but spreading it in the garden, forest, or fields can have both positive and negative effects. In this article, we delve into the question of using ash in the garden, providing you with the information you need to utilize it wisely and eco-consciously.

Ash – A Traditional Source of Fertilizer

Using ash as a fertilizer is a tradition that dates back a long time. Ash contains a Using ash as a fertilizer is a traditional practice that has been around for a long time. Ash contains various minerals essential for plant growth. According to a study by the Swedish Energy Agency (ER 2019:24), typical wood pellet ash may contain the following per 100 grams:

Potassium (K): 4000-5000 mg per 100 grams. Strengthens stems and roots, enhances disease resistance
Phosphorus (P): 500-1000 mg per 100 grams. Stimulates flowering and root formation.
Calcium (Ca): 1000-2000 mg per 100 grams. Improves soil structure, essential for chlorophyll formation.
Magnesium (Mg): 200-500 mg per 100 grams. Vital for photosynthesis and plant energy production.

Manganese (Mn): 50-100 mg per 100 grams. Essential for photosynthesis and chlorophyll formation.
Iron (Fe): 100-200 mg per 100 grams. Crucial for chlorophyll formation and nitrogen fixation.
Zinc (Zn): 20-50 mg per 100 grams. Important for enzyme activity and growth.
Copper (Cu): 5-10 mg per 100 grams. Essential for photosynthesis and disease resistance.

Advantages of Using Ash in the Garden

Source of Nutrients: Ash provides essential minerals to the soil, enhancing plant growth and resilience.
Increases pH: Ash is alkaline and can increase the pH of the soil. This can benefit plants that thrive in lime-rich soil, such as roses and hedges.
Pest Control: Some research suggests that ash may have a deterrent effect on slugs. A study from SLU in 2017 (pdf) indicated that spread ash can create a barrier that slugs dislike crossing.

Disadvantages of Using Ash in the Garden

Let’s explore why ash might be more problematic than you realize:

Heavy Metals: Ash contains heavy metals like lead and cadmium, which can accumulate in the soil over time, posing risks to the environment and health.
Nutrient Imbalance: Ash doesn’t contain all the nutrients plants need. Solely relying on ash can lead to deficiencies and imbalances in the soil’s nutrient content.
Salts: Ash contains salts, primarily potassium sulfate and potassium chloride, which can be harmful to plants in high concentrations. The risk of damage increases in dry conditions. The salt in ash doesn’t break down in the soil but can leach out with rainfall.

According to a study by the Swedish Environmental Protection Agency (2019), pellet boiler ash may contain the following concentrations of heavy metals per 100 grams:

- Lead: 0.5-10 mg
- Cadmium: 0.2-2 mg
- Mercury: 0.005-0.05 mg
- Arsenic: 0.5-5 mg

Unfortunately, you can do little to decrease the heavy metal content in ash significantly. Regular internal pellet stove maintenance is the most effective way to minimize it. While pellet quality can vary, no evidence suggests lower-quality pellets contain less heavy metals. The heavy metals are primarily sourced from the tree’s growing environment and the machinery used in pellet production.

Is it possible to use ash in compost?

Composting is a natural process in which microorganisms break down organic waste. To maintain a stable pH value, it can be beneficial to use ash in your compost. Ash acts like lime and helps to raise the soil’s pH. However, it’s essential to use the right amount of ash and choose the appropriate type of ash to avoid any negative effects on the compost.

A pH level that is too low (below 6.5) can inhibit the growth of the microorganisms essential for the decomposition process, leading to slower composting.

An optimum pH range of 6.5 to 8 creates a favourable environment for microorganisms to efficiently break down organic matter during composting.

Having a pH above 8 can slow down composting and prevent the growth of certain microorganisms.

Small amounts of ash can be added to compost to create an optimal pH balance, but it’s important not to use too much as this can make the pH too high. It’s crucial to note that not all types of ash are suitable for composting. Ash from burnt materials such as laminated or treated wood should be avoided as these contain substances that are not intended for nature to break down. The same applies to ash from newspapers, flyers, cardboard boxes and other treated paper. These ashes should be disposed of at a recycling station.

Pellet ash from natural wood is safe for compost, lawns, and flower beds. It contains the essential nutrients potassium, phosphorus, and calcium that plants need.

Here are some additional tips:

Make sure to wait until the ash is completely cold before adding it to the compost.
Add only small amounts of ash at a time. A good guideline is to not add more ash than you can cover with your palm. Then mix the ash thoroughly with the compost material.
You can test the pH level of your compost using a testing kit. If the pH level is high after adding ash, you can lower it by adding coffee grounds or rotting leaves.

Considerations for Fertilizing with Ash

Ash can be a valuable nutrient source for your plants, but it’s essential to use it correctly. Using too much ash can be harmful, so testing your soil and using ash sparingly is crucial.

Test Your Soil First: Before using ash, test your soil’s pH level and nutrient content. Ash is alkaline and can raise the soil’s pH level, which may harm some plants. Soil test kits are available in garden stores.
Use sparingly: A maximum of 1-2 dl of ash per square meter per year is recommended. Using too much ash can cause nutrient imbalances and harm plants.
Supplement with Other Fertilizers: Ash is not a complete fertilizer. It should be used in combination with other fertilizers to provide balanced nutrition to plants.
Avoid Using Ash in High pH Soil: If your soil already has a high pH level, avoid using ash. It can further elevate the pH level, which may harm plants.

By following these tips, you can use ash safely and effectively to benefit your plants.

Key Takeaways

Ash should not be used as the sole fertilizer source.
Mix ash into the soil, 1-2 dl per square meter.
Water the soil after spreading the ash.
Use ash in the fall or spring when the soil isn’t frozen.

Why Is Pellvac Writing an Article on Fertilizing with Ash?

We are aware that many pellet burners in Sweden, Finland, Denmark, and Germany use our ash dust collector, Whirlwind. Our customers are usually homeowners who have gardens. While it may be tempting to simply collect the ash with Whirlwind and spread it on the lawn or flower beds, it’s important to remember that ash can contain heavy metals that can be harmful to plants, animals, and humans in large quantities. We recommend using ash sparingly and disposing of any excess as residual waste, which should be sealed in a bag or container.

Hey, just a quick tip – if you need to clean up ash or coarse dust but don’t have a Whirlwind, remember that Pellvac is the only manufacturer of this innovative cyclone dust collector. You can purchase it directly on our website.