Container Planting with Biochar
Jul 09, 2021
Knock Your Gardening up a Notch!
By: Sheila McEwen
I first learned about biochar last year while watching Rosario Dawson's award-winning documentary The Need To GROW.
I was immediately intrigued by the concept of applying charred cooking waste to a vegetable garden to boost yields while reducing the need to add water and fertilizer. So I began a quest to learn more about the glittering horticultural black gold called biochar and to experiment with biochar in my thirsty container garden.
What is biochar?
Depending on the information source, biochar is either a high-grade type of charcoal or a “charcoal-like” substance with properties superior to those of charcoal. Regardless, all sources tend to agree that biochar differs from common charcoal—say, the type used for cooking briquettes—in how it is made and in its extraordinary beneficial uses.
How biochar is made
Biochar is made in a process called pyrolysis, which exposes carbon-rich organic matter to extreme heat with little or no access to oxygen. All sources of this carbon-rich matter were once part of a living organism. Sources typically include plant waste, like wood and corn stalks, by-products of a biological process, like manure and sewage, or a combination of the two, like livestock bedding.
Biochar’s beneficial uses
Biochar increases the soil’s moisture retention, which reduces the need to irrigate crops. Biochar also helps nutrients to move through the soil more efficiently, which reduces the need to add fertilizers. What’s more, biochar also helps to restore organic carbon, filter soil contaminants, neutralize acidic soils, and suppress odors in manure applications! But, for now, I’ll just focus on biochar’s benefits to plants.
My biochar experiment
I’m not a farmer, just a hobby gardener dabbling with varying success at growing vegetables in containers. My interest in biochar was mostly to cut down on watering during the blistering heat waves that are becoming the norm in southern Ontario’s growing season. I’ve had to water container plants morning and evening on days when the temperature exceeded 30 degrees Celsius.
As if the challenge of container planting were not enough, I recently transitioned to veganic gardening and no longer use synthetic fertilizers or animal-derived compost. So I was curious to see how biochar could improve nutrient uptake by plants confined to a vegan diet within tiny, plastic-bound biospheres.
Canadian-made biochar
My search for Canadian biochar suppliers located AirTerra, an Alberta company that produces SoilMatrix, a high-grade biochar made from wood residue. I particularly liked AirTerra’s assurance that its product is free of animal waste and of toxic substances like pathogens and polycyclic aromatic hydrocarbons (PAHs). So I ordered several boxes of SoilMatrix and began experimenting with biochar.
Putting biochar to work
During a phone chat on how to get started, AirTerra President and CEO Rob Lavoie advised me to inoculate the biochar with compost before combining it with my potting soil. Biochar by itself contains no nutrients but it provides pathways for beneficial microbes to transfer nutrients and moisture from the compost to the plant roots.
As Rob explains, “The soil ingredients—sand grains, silt, humus (dead plant material), clay, and soil organic carbon—play an important part in enabling roots and microbiology to uptake nutrients destined to feed plants. The key requirement for nutrients to be bioavailable is their “solubility”. Roots, bacteria, and fungi can only take up nutrients that have been solubilized (in solution with water.) This is where biochar can help.
“Biochar assists nutrient uptake through its ability to support the solubilisation of nutrients on its large surface area of positively and negatively charged pore structure. Moreover, the pores themselves make excellent storage locations for moisture. Together, moisture stored (absorbed) in biochar pores and nutrients stored (adsorbed) along its charged cellular walls become more available for roots, bacteria, and fungi. Mycorrhizal fungi provide a transportation paths for nutrients and moisture stored in biochar particles to get to the roots. “
So, over the fall and winter months of 2020-21, I added biochar to ground tree leaves and kitchen waste and kept the mixture moist and aerated. By the spring, most of the mixture resembled dark soil. To prepare my plant containers, I combined the biochar blend with potting mix containing soil and mycorrhizal fungi. Those were the only ingredients my plants would access for the full growing season, apart from any nutrients inadvertently delivered by the birds and insects in my backyard.
When to use biochar
If you’re also considering biochar amendment to your gardens or fields, Rob cautions that you first should ensure the nutrients in your soil are solubilized. He explains,
“Saying that biochar is necessary for soil nutrients to be made available for plants would be a vast over statement! Roots can access nutrients directly if the root itself encounters nutrients that are solubilized. For this to occur, the soil must be moist with solubilized nitrogen, phosphorous, and potassium (to name only the top three macro nutrients). If the soil is dry, the nutrients are in a crystalized solid form, leaving them unavailable to plant roots. Also, nutrients that have not been adsorbed onto a surface or some type of surface area can easily be washed away in the rains, and this is the fate of a soil with too little soil organic carbon content in the form of dead plant or microbial material or biochar. It is the soil life in the form of bacteria, fungi and earthworms that perform the work of converting solid organic material into these solubilized nutrients.”
To make the most of your biochar investment, Rob offers these tips:
- Don’t use biochar for soil that is already rich in organic carbon (compost, dead plant material, wood chips, mulch, etc.) Organic-rich soils already have the surface area needed to make nutrients available for plants.
- If adding biochar directly to soils lacking in organic carbon,
- first amend the soil with rich compost and worm castings. This will help make the nutrients more available in a solubilized form, then
- add the biochar between layers of compost to help maintain the organic carbon level at a healthy level.
- Instead, and ideally, co-compost the biochar with organic residues before adding it to the soil.
Results
Although it’s too early in the season to detect biochar’s impact on food yield, all the container plants are looking vibrant and little fruits are beginning to emerge on their fragile branches. I’m happy to find that my plants need less frequent watering than they previously had on comparatively hot, dry days. Biochar may be one of the reasons.
If you’re interested in learning more about AirTerra’s Soil Matrix biochar, please visit www.airterra.ca
Sheila McEwen is a freelance technical writer and a novice veganic gardener.
This blog post is brought to you by friends of Reimagine Agriculture, Mercy For Animals.
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