Biochar super charges your potting mix, with a little making a big difference. I personally stock and use Kiwichar Biochar, which is 100% NZ sourced biochar, made from organic, untreated wood. Here's how biochar benefits indoor plants, how to charge and inoculate (or activate) biochar, and how much biochar to use for indoor plants.
What are the benefits of biochar for indoor plants?
Biochar helps increase both water retention, nutrient retention and drainage to improve soil quality. Biochar's also been found to help plants resist and fight off fungal disease, and increase soil fertility to support growth. Biochar amended soil has also been shown to help plants better handle water extremes of both draught and flooding.
Biochar's also been shown to increase root health, promoting stronger root growth. It's both light and highly porous, making an ideal habitat for beneficial soil microorganisms to set-up home, which promotes better soil and plant health.
What's in biochar?
The name biochar comes from bios (from Greek and Latin, meaning life), and char (from charcoal). The history of biochar dates back centuries to the Brazilian Amazon. The Kiwichar brand of biochar is made from organic, untreated wood, that's been turned into charcoal by heating to high temperatures with little to no oxygen (called pryolyzed).
How do you use biochar?
The most popular use is as a soil amendment to increase nutrient and water retention, added to your store-bought potting mix while still keeping it airy and free-draining - or when you want to go the DIY path and create your own potting mix. It's best to activate biochar before use (more about that coming up).
How much biochar do you use?
For adding biochar to potting mix, Kiwichar recommends a 10% ratio, and gives the example of 1kg biochar to 40 litres of soil, or for smaller quantities, that's around 125 grams biochar per 5 litres of potting mix.
However I personally recommend a much lower percent - around 2% - if you're creating a more free-draining mix. That would be about 25 grams biochar per 5 litres of potting mix. For plants that prefer things more on the moist side, like Ferns, Peace Lily, Calathea and more, use the 5% to 10% ratio.
For adding biochar to an already potted plant, simply sprinkle a thin layer of biochar over the top surface of the pot. Over time this will be watered down into the substrate. However the best method is to mix biochar in with the potting mix before potting up.
How do you charge or activate biochar?
Biochar doesn't contain microorganisms or nutrients out of the bag so it is recommended to biocharge or 'activate' it before use. You ideally want to both charge (by adding nutrients), and innoculate (add microbes), your fresh biochar before use.
In outdoor gardening a popular method is to mix biochar 50/50 with compost or compost tea in a container, and leave it outdoors to weather for 10 days, before adding it into your garden.
For indoor plants, you can still use the outdoor method then mix the charged biochar in with your indoor potting mix. However the method I use is to charge it with a nutrient bath. Scoop the amount of biochar you need out of the bag, make up your nutrient mixture, then soak your biochar in the nutrient water for a least 3 days uncovered, before mixing it with your potting mix ready to pot up.
You can create with your own custom concoction, but I like using a mix of organic and inorganic nutrient sources for a nice complete mix. Common choices are worm castings, NPK fertiliser, seaweed and more.
For mine I use an NPK fertiliser plus seaweed flake. I make both up at the normal dose based on the litres of water (you want enough water so the biochar floats), add the biochar in, and let it soak for at least 3 days. Rather than sieve out the biochar, when it's ready, I just mix the nutrient water, biochar and all, in with the potting mix, and pot up as usual. You can pour the mix through a sieve so you're just left with the charged biochar, and save the leftover nutrient water for your plants.
Safety when working with biochar
Exactly the same as all substrates, potting soil and soil amendments, when handling biochar, always wear gloves and wear a mask. Even if you've worn gloves, wash your hands after potting up. Biochar can be dusty, so wearing a mask is recommended. It's ideal to dampen biochar and keep it moist when working with it.
Where can you buy biochar in New Zealand?
From me, here at Love That Leaf. I sell Kiwichar Biochar >