How to Make Garden Biochar

Plan to make and add biochar to your garden in the spring, before you plant. The day needs to be windless, for safety, and overcast, if possible, for a higher humidity level.

Use a shovel to dig a trench in your garden area. The trench should not be so large you will not be able to monitor or control the fire built in it. Your trench can be any manageable size, but the deeper you dig it, the more biochar you can introduce into your garden soil. You can also dig a shallower trench, then use a garden fork to loosen the soil in the bottom of the trench. This allows the biochar to enter your soil, deeper, after it is made.

Fill the trench with dry plant material, twigs, leaves, needles and branches. Place a few wadded up pieces of paper or newspaper in with the plant material to help it catch fire and burn. You do not want to use an accelerator, like gasoline or lighter fluid, to start or maintain the fire. Chemical accelerators will contaminate your soil.

Light the plant material and paper, using matches. You want the plant material in the trench to catch fire quickly, burning hot, in the beginning. The drier your plant material is, the easier it will quickly catch fire and burn.

Watch the smoke your fire is producing to judge how the plant material is burning and making biochar. White smoke appears at the beginning of the fire, indicating that moisture is being burnt off. As the plant material's resins and sugar burn, the smoke becomes yellow. Finally, the smoke will be grayish-blue as the plant material begins to turn into charcoal.

Use a shovel to cover the burning plant material with about 1 inch of soil when you see the smoke is grayish-blue. This layer slows the burning material to smoldering by reducing the oxygen and creates the charcoal.

Douse the smoldering fire with water when you see the plant material has turned into charcoal chunks. Completely douse and put out the fire at this point. Allowing the plant material to continue burning will turn it into ash, defeating the purpose of introducing biochar into your soil.

Amend your garden soil using the biochar and compost. The combination of biochar and compost will give your plants the most benefit of the compost nutrients quicker.