Biochar does wonders for houseplants—here’s how to use it
Do you tend to overwater your houseplants or forget to fertilize them? Let biochar come to the rescue. It helps keep the soil airy and properly moist, and you can also infuse it with nutrients that dissolve gradually for your plants to absorb.
What is biochar?
Biochar is a lightweight, porous material produced from biomass at high temperatures in low-oxygen conditions. There are many different versions available. You can even make your own biochar, for instance, from branches in your garden.
What are the benefits of biochar for houseplants?
Biochar helps balance moisture and nutrient levels in the soil and boosts microbial activity. It also provides long-lasting aeration, which is vital for root health.
Especially in large pots, biochar placed at the bottom creates a water and nutrient reservoir. This directs roots to grow deep, helping the plant tolerate drought more effectively.
Biochar is available in different coarseness levels. How do I choose the right one?
Finely ground biochar (0–2 mm) is best for improving the soil’s water retention. It helps extend watering intervals and lowers the risk of overwatering. It’s particularly useful for species that enjoy consistently moist conditions, such as ferns and aroids.
Coarse biochar (1–10 mm) aerates the soil and improves drainage. It’s well-suited for orchids and houseplants that are grown in large pots and need repotting infrequently.
We often hear about charging biochar. What does that mean?
Charging means infusing biochar with nutrients. You can either add untreated biochar in the soil of your plant and let it charge on its own, or pre-load it with nutrients before adding it into the soil.
If you add uncharged biochar to the plant’s soil, it will draw nutrients from the soil over the months. During this time, you should fertilize a bit more than usual to compensate for the nutrients held by the biochar. Once it has charged in the soil, the biochar will fertilize the plant steadily for a long time.
Another way to charge biochar is to soak it for 24 hours in a fertilizer solution, chicken manure water, diluted urine, or bokashi liquid before use. A mild solution is absorbed more evenly, so use only half the recommended amount of fertilizer. You’ll need about half a liter of liquid for each liter of biochar.
In addition to untreated biochar, pre-charged biochar products are also available.
How can I incorporate biochar into houseplant soil?
You can slip pieces of biochar into holes you’ve made in the soil, or mix it into slightly moist soil when planting or repotting. A good amount is 5–10 percent of the total soil volume.
A third option is to lay a 2–3 centimeter layer of biochar at the bottom of the pot for drainage. Especially in large pots, biochar placed at the bottom creates a water and nutrient reservoir. This directs roots to grow deep, helping the plant tolerate drought more effectively.
The biochar’s pores fill with water over 2–3 weeks, so you’ll need to water the plant a bit more during this period. Over about six months, the biochar in the soil becomes a nutrient source, reducing the need for fertilization.
Markku Suutari of Carbons Finland was interviewed for this article.
