Biochar is the fancy name for charcoal used in gardening and farming.
See photos below for a simple method to prepare biochar for your garden soil.
Biochar doesn’t rot, absorbs fertilizers, helps beneficial fungi, and stays in the ground for hundreds or thousands of years.
Some believe biochar could be a way to sequester (bury) carbon while improving soils.
Terra preta, literally “black earth” in Portuguese, is the name for ancient fertile soils in the Amazon river basin that contain charcoal.
Terra preta soils were created by humans between 450 BC and AD 950 in what is now Brazilian rain forest. Centuries later, local farmers use and even dig up and sell terra preta as valuable compost.
Charcoal has millions of internal pores that provides a huge surface area on which fertilizers can adsorb (stick) rather than being leached out of soil.
The same charcoal nooks and crannies create homes, safe from hungry earthworms, for beneficial microbes and fungi.
Used in the garden, charcoal lowers soil acidity and improves drainage.
Gardeners are still experimenting with biochar to make their own equivalent of fertile Amazonian terra preta.
Here is a longer article on bio char for gardening and farming.
Would you like to try using charcoal in your garden?
Here are some simple steps.
Begin with Natural Lump Charcoal
You can buy a bag of lump charcoal in the barbecue section of your local home store or from various sellers on Amazon.
This is how natural lump charcoal looks, photo courtesy of Amazon. Click for close-up.
Charcoal briquettes contain paraffin (to hold their shape) and sometimes kerosene. Natural lump charcoal is just plain biochar.
Produced by “pyrolysis” or heating in the absence of oxygen, natural charcoal is very light and tinkles with a pleasant sound. In fact, a “charcoal xylophone” is made with Binchōtan, Japanese “white charcoal.”
Of course, you can draw pictures with charcoal. A 10-pound bag could produce quite a portfolio!
But here we are talking about crushing charcoal and adding it to your garden soil.
Don’t get too excited about how much carbon you can personally take out of circulation by burying it in your garden.
A bag will just about offset the carbon released during the car trip to and from the store to buy it.
You can make charcoal yourself if you have a source of wood, some old oil barrels, and understanding neighbors. But for small quantities, it’s more practical just to buy a bag. Smaller pieces that barbecue aficionados dislike are just fine for gardeners.
Crush the Charcoal
This is the only moderately tricky part. After trying to break it up in a bucket, I put some cheap natural lump charcoal into a brightly colored pillow case, and hit it with a log. Worked quite well.
Don’t breathe the dust, and remember to launder and return the pillowcase if it was borrowed from a friend or family member. If they ask about the small fabric tears or permanent discoloration, just shrug and say, “I’m a heavy sleeper.”
Other pillow case colors should work fine, too.
Add Fertilizer, Compost or Urine
Charcoal will take up nutrients from your soil, so it’s best to add compost or other fertilizer. Adding nutrients to the tiny pores is called “charging” and accelerates the benefits of biochar.
Some people add urine to their biochar. Your neighbors make get a kick out of this. Or not. Use good judgement
I was a bit dehydrated so I just added the crushed charcoal to water mixed with a few tablespoons of granular fertilizer and left it to soak for a couple of days.
Add to SoiI
I have unscientifically added the fertilizer-soaked biochar to soil in amounts not carefully measured.
Charcoal certainly makes the soil look dark and rich.
I also grind charcoal biochar into very small pieces using a cheap corn grinder
It worked perfectly! Click on the image below to shop
Get a cheap one. Based on looking around Amazon, these grain grinders all have the same design and very rough construction. I had to adjust the hopper with some gentle hammering and added some washers to space out the grinder plate. The handle falls off until you slip in back on.
Rocket engineering it’s not but many customers complain about these cheap corn grinders. Welcome to the Third World where equipment is cheap, shoddily constructed, requires adjustment, but works.
Does the biochar do any good? No idea. So far it certainly appears to do no harm. Tomatoes planted with charcoal are thriving.
I know charcoal “sweetens” soil (raises pH, so good for acid soils) but haven’t tested that yet.
I just want to know if plants do better with charcoal in the soil.
I suspect that soils prone to leaching (sandy soils) benefit from anything that hangs onto N, P, K and other nutrients. And, like perlite, compost, etc. just about anything that improves drainage is good for heavy soils.
The idea that charcoal won’t decompose as quickly as other organic amendments is appealing.
But I’m a charcoal agnostic so far. If you figure it out, please comment!
Update: Research on biochar has exploded since this article was written.
One exciting finding: “Biochar application to soils has potential to simultaneously improve soil fertility and store carbon to aid climate change mitigation. While many studies have shown positive effects on plant yields, much less is known about the synergies between biochar and plant growth promoting microbes, such as mycorrhizal fungi. We present the first evidence that arbuscular mycorrhizal (AM) fungi can use biochar as a physical growth matrix and nutrient source.”
Here’s the good part about biochar and mycorrhizae hyphae, the “roots” of symbiotic plant fungi
“We conclude that AM fungal hyphae access microsites within biochar, that are too small for most plant roots to enter (<10 μm), and can hence mediate plant phosphorus uptake from the biochar.” Below is the link to the article by Edith C.Hammer, Department of Chemical and Biochemical Engineering, ECO, Technical University of Denmark and co-researchers in Sweden and Germany.
Image courtesy Amazon
In other words, biochar hides away phosphorus from plant roots but makes it available to mycorrhizae.
As we know, plants with plenty of phosphorus aren’t as likely to hook up with their “fungus brothers.” Overdo the phosphorus and myccorizae don’t proliferate in your soil. “Heavy usage of phosphorus fertilizer can inhibit mycorrhizal colonization and growth.”
This suggests to me that biochar could be a way to feed phosphorus to plants but only through the mediation of mycorrizae, which also supply water and improve soil. In other words, activate your char with phosphorus to encourage the obligate symbiotic fungus but go light on phosphorus directly available to plant roots.
Mycorrhizae already grow in your soil but you can buy more
Biochar-Based Fertilization with Liquid Nutrient Enrichment: 21 Field Trials Covering 13 Crop Species in Nepal by Hans-Peter Schmidt et al
This research showed that “low-dosage root zone application of organic biochar-based fertilizers caused substantial yield increases.” These researchers used urine on biochar. They found that cow urine-enriched biochar blended with compost resulted on average 123% ± 76·7% higher yields compared with cow urine-blended compost and outcompeted NPK-enriched biochar by 103% ± 12·4%.
I don’t sell urine but you might want to buy some books on biochar.