Biochar for Home Gardening

Charcoal or “biochar” has for centuries improved soils, including Amazonian terra preta or “black earth.” Would you like to try using charcoal in your garden? Learn how to prepare garden charcoal through photos and scholarly, easy, funny text. Adding urine is optional.

Photo of natural charcoal or biochar for gardening

Biochar is the new, 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 pleasingly.  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 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.

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 probably 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.

Photo of crushed charcoal in a pillow case

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.

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.

Photo of gardening charcoal with fertilizer added

Add to SoiI

I have started unscientifically adding the fertilizer-soaked biochar to soil in amounts not carefully measured.

Charcoal certainly makes the soil look dark and rich.

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’m very interested in the experiences of other gardeners.

Not looking for high-minded carbon-offset hopes, so I can drive my car around guilt-free, or spooky “biochar” crystal pyramid power belief structures.

I just want to know if plants do better with charcoal in the soil.Photo of garden soil for biochar gardening charcoal

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!

Here are some scholarly articles on biochar and a link to a article on how to add biochar to compost.

And some books