What Is Biochar?

Biochar is a purified, charcoal-like material that’s created by burning organic matter in a low-oxygen environment. While most fires utilize the combustion process, biochar is created via pyrolysis, which only occurs in the absence of oxygen. Biochar is usually made from wood, but it can also be created by burning plant debris, livestock bedding, manure, and other natural items.

Biochar is sometimes sold at garden centers in chunks or powdered form, but it can be made at home using leftover garden debris, fallen sticks, and other yard waste. Thanks to its high porosity, biochar holds onto moisture and nutrients well, and it’s often preloaded or “charged” with compost, manure, or other nutrient-rich materials before application.

Biochar Benefits

Due to its large surface area and highly porous nature, charged biochar acts like a sponge and slowly releases nutrients and moisture over time. This helps plants grow better and improves the health of garden soil. While biochar has many applications outside the garden, the main reasons why you might want to use biochar in your garden or with potted plants include:

• Better water retention. Biochar holds onto moisture and slowly releases water to plant roots. It improves the soil’s water retention and is particularly beneficial in dry and sandy gardens.
• Reduced fertilizer needs. In addition to moisture retention, biochar also locks onto plant nutrients, meaning you won’t need to use as much fertilizer when biochar is in your garden. Even better, biochar reduces fertilizer and nutrient leaching.
• Less acidic soil. Biochar has a relatively high pH and can be used to neutralize overly acidic soils. It doesn’t need to be applied as often as other pH-balancing amendments.
• Fewer plant diseases. Once applied in the garden, biochar increases the activity of beneficial microbes, and it may even suppress some plant diseases, like damping off and root rot.
• Improved soil structure. While biochar increases water retention in sandy gardens, it’s also useful for breaking up and aerating clay-heavy soils. This helps plant roots grow and prevents soil compaction.

Healthier plants. By suppressing plant diseases and increasing nutrient and water retention, biochar improves the overall health of garden plants. It can also enhance the growth of houseplants, seedlings, and container gardens.

How to Make Biochar

Biochar can only be created in a low-oxygen environment, and you can’t make biochar in your fireplace or firepit. Instead, biochar is typically made in metal drums that are safe to burn in and at least 30 to 40 gallons in size. Before you start, make sure the drum is clean and has never been used to hold chemicals or other materials you wouldn’t want near your food garden.

1. Gather the Materials

Gather twigs, sticks, logs, dried leaves, and other plant debris in your garden. For safety, only use untreated wood that has never been painted or stained.

2. Make a Fire

Fill the base of the metal drum with the organic materials and light them on fire. While you’re working, follow proper fire safety protocols and never leave the fire unattended.

3. Add Soil

Let the fire burn until it produces bluish-gray smoke, and then shovel soil on top of it. This should smother the flames but allow the organic matter to continue to burn beneath the soil in a low-oxygen environment, which is essential for creating quality biochar.

4. Cool It Down

Once the organic materials are charred and dark, extinguish the fire with water and allow everything to cool down.

5. Break It Up

Scoop the biochar out of the burn barrel and gather it in buckets or bags. You can store chunks of biochar as is, but biochar should be broken up into small, ¼-inch pieces before applying it to your garden or potted plants. You can use a garden tamper to break up biochar in a bucket or seal biochar pieces in a sturdy bag and pulverize them with a mallet.

6. Charge the Biochar

Pure biochar can’t pull nutrients and water away from plant roots if it's “charged” or “loaded” before application. Charging biochar is easy and can be done in several ways.

In a compost pile: The easiest way to charge biochar is to mix biochar into your compost pile. Allow the biochar to charge in the compost for three to four months before adding the biochar and compost blend to your garden.

With dry ingredients: Blend 10 to 50 percent biochar with compost, aged manure, or worm castings in a bucket or pile. Mix the biochar with your dry ingredients, add some water, and allow the biochar to charge in the ingredients for about a month before application.

Wet ingredients: The fastest way to charge biochar is with wet ingredients like compost tea and liquid organic fertilizer. Saturate the biochar with your product of choice, wait 1 to 3 days, and then apply the charged biochar to your garden.

How to Use Biochar for Healthier Plants

Pure biochar can be incorporated into your garden or potting soil, but it is easier to apply when mixed with compost or aged manure. If you’re new to working with biochar, here are some of the most popular ways to use this versatile amendment.

• As a soil additive: To improve soil structure and health, sprinkle charged biochar directly over your garden and mix it into the top 6 inches of soil. Biochar is a relatively stable amendment; you only need to add it to your garden every few years.
• As a top dressing: Another option is to apply a light dusting of charged biochar over your soil once a year. If you’re using biochar blended with compost or aged manure, apply about 1 to 2 inches of the mixture.
• As a side dressing: Biochar, with or without added compost, can also be sprinkled around plants during the growing season. Just be sure to keep the biochar and compost a few inches away from the plant stems to avoid issues with rot.
• As a potting mix additive: Vermiculite and perlite are often blended into potting mixes to improve drainage and moisture retention. However, you can replace either of these ingredients with biochar for a more affordable and eco-friendly potting mix.