Add some super powers to your potting mix with biochar. This is the Kiwichar brand, which is 100% NZ sourced biochar, made from organic, untreated wood. It seems such a simple ingredient to add to your potting mix, yet has so many impressive benefits for our plants. 

What are the benefits of biochar for 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. It's been shown to increase soil fertility to support growth - and good news for both over-waterers and under-waterers - biochar amended soil has also been shown to help plants better handle water extremes of both draught and flooding. It's also been shown to increase root health, promoting stronger root growth. Biochar is both light and highly porous, making an ideal habitat for beneficial soil microorganisms to set-up home, which promotes better soil and plant health. However, like any substrate, soil amendment or fertiliser, you should still check it's what your plants need.    

What is 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. Kiwichar 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 in your store-bought potting mix, or when you want to go the DIY path and create your own perfect potting mix. It's best to activate biochar before use (more about that coming up).

For adding to potting mix: You can experiment with your own levels, but Kiwichar recommends a 10% ratio, and give 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 lower percent - around 2% - if you're creating a more free-draining mix. That would be about 25 grams biochar mixed in well per 5 litres of potting mix.

For adding to an already potted plant: Simply sprinkle a very 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 big is the bag?

One bag of Kiwichar measures about 20cms wide by 33cms tall and contains 3 litres of biochar. A little goes a long way, so this smallest size is ideal for indoor plant hobbyists.  Biochar doesn't decompose and is a very stable, long-lasting substrate, so you can store it in the resealable Kiwichar bag for the next time you need to repot.

Does biochar need 'charging'?

Biochar doesn't contain microorganisms or nutrients out of the bag so yes, 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. Let it soak for a few 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. 

Safety when working with biochar

Exactly the same as you should with all substrates, including 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.