Charcoal can be used in compost, pots, or as mulch to improve drainage, speed decomposition, and retain vital nutrients.
You may know that gardeners and farmers use charcoal in their gardens, but it's likely not the kind you're thinking of. The type of charcoal used for grilling, known as grilling briquettes, is made from compressed sawdust, coal, and various chemical additives meant for fuel, making it unsuitable for gardening.
On the other hand, beneficial charcoals, such as biochar and lump charcoal, can significantly enhance garden health. These types of charcoal can improve soil structure and aeration, enhance water and nutrient retention, neutralize toxins and impurities, and boost microbial activity in the soil. Ahead, gardening experts discuss everything you need to know about using charcoal in the garden.
While most people view charcoal primarily as a fuel for barbecues, there are other charcoal products that can be used in the garden. Choosing the right type is essential for the health and productivity of your plants. According to experts, these are the best and most common kinds of charcoal you can add to your soil.
Biochar is a solid, carbon-rich material specifically designed for soil application, says Deborah Aller, director of the New York Center for Organics Recycling and Education. It is created when organic material is heated in a low-to-no oxygen environment through a process called pyrolysis. Pyrolysis stabilizes the carbon, making it a long-lasting soil amendment with exceptional porosity. It helps the soil retain water and nutrients and serves as a home for microorganisms.
"In theory, any organic material, also known as feedstock, can be used to make biochar," says Aller. "Feedstocks range from woody waste to agricultural byproducts and invasive plants to manures," Aller explains. The most common feedstock used is woody waste material. She notes that it is essential for the feedstock material to be free of contaminants before adding it to soil.
This all-natural product is made from 100 percent wood and contains no toxic additives. The wood is burned in a low-oxygen environment until it is carbonized, resulting in irregularly shaped pieces of pure carbonized wood. It can be applied in the garden to add organic matter, improve soil structure, and help retain essential nutrients, such as nitrogen.
Lump charcoal ash is the light grey, powdery residue left behind after the lump charcoal has been burned. This ash is rich in essential nutrients, including potassium, calcium, phosphorus, magnesium, copper, iron, and zinc. However, it can also raise the soil pH, so avoid adding large amounts.
Activated charcoal is a fine, black powder obtained from carbon-rich materials like coal, coconut shells, or wood, that have been burnt or activated at high temperatures. This creates numerous tiny pores, which increase surface area and adsorption ability on the charcoal particles.
Now that you know the distinctions of this beneficial garden amendment, Manjot Kaur Sidhu, assistant professor and ornamental horticulture specialist at the University of Maine, shares useful ways to utilize it in the garden, benefiting both your soil and plants.
Adding charcoal to soil can help to improve its structure, porosity, water-holding capacity, and nutrient retention, says Sidhu. It can also be used as a soil amendment to neutralize soil acidity.
Adding charcoal to a quickens the composting process as the structure of charcoal serves as a habitat for beneficial microbes required for composting, says Sidhu. It also helps neutralize unpleasant odors and balance the carbon-to-nitrogen ratio in the compost pile.
A 2-inch layer of activated charcoal can be placed at the bottom of containers, below the potting soil. "It helps to provide air circulation for the roots, provide drainage (especially in containers without drainage holes), prevent fungal diseases, and prevent mineral toxicity by soaking up excess nutrients," Sidhu says.
Charcoal can serve as a mulch by creating a protective, porous layer on the soil surface, much like organic mulches. This layer helps and retain soil moisture. Additionally, the porous nature of charcoal acts like a magnet for nutrients, holding onto them and preventing them from leaching away. This allows the nutrients to remain available for plants to use over time.