I firmly believe that healthy plants start with healthy soil. And fall is the perfect time to amend your garden for future growing seasons. Many gardeners consider adding fertilizer for nutrients and adjusting the soil pH, but an increasing number of growers are becoming interested in amendments like biochar to build soil in fall.

Biochar isn’t a fertilizer, so it won’t solve issues with nutrient deficiencies. Nor will it add beneficial bacteria and fungi to your soil. However, it can help improve soil structure and increase the impact of both nutrients and microorganisms.

Since this is a less common amendment, you may wonder when and how to add it. I’ll share a few ways you can improve fall soil with biochar, no matter the scale of your garden.

What Is Biochar?

Soil enriched with charcoal holds water for longer.

Biochar is a stable form of carbon that forms when organic material is heated at high temperatures in the absence of oxygen, a process known as pyrolysis. The end material resembles charcoal, but has distinct properties and applications.

There are many different types. These materials vary depending on the organic materials they were made from. Some common feedstock materials include wood, manure, and waste materials such as corn stubble.

You can make biochar at home if you’re up for a new and somewhat intensive process, or purchase it in stores. Since it is primarily composed of carbon, it won’t add large amounts of key nutrients to the soil. However, its chemical properties make it an excellent amendment for improving soil structure and physical characteristics.

Benefits of Biochar

Soil amended with charcoal keeps nutrients from leaching.

Biochar improves fall soil in numerous ways, as long as you apply it correctly. Its porous nature and slow breakdown time are responsible for many of its benefits.

While it may sound like a magic material, recognize that this doesn’t affect all soils equally. One study found that adding biochar to soil resulted in a 10% average increase in crop productivity, but results ranged from a 28% decrease to a 39% increase.

Generally, it offers greater benefits to acidic soils and those with coarse textures. If you’re growing in a sandy or loamy soil with a low pH, go ahead and add this organic material to your garden! But if you’re growing in heavy clay or soils with a high pH, you should probably stay away from this material.

Provided that your soil reacts well, here are some of the benefits you’ll experience.

Ways to Add Biochar to Fall Soil

Carbon-rich material keeps nutrients available for next season.

If you decide that biochar can improve your soil, fall is a great time to add it to the ground. Its properties will help hold nutrients in place over winter, and it will have time to act on soil pH before the spring growing season begins.

The best way to boost fall soil with biochar depends on your context. Your garden size, available tools, and soil type are just a few factors to consider. Regardless of your conditions, here are a few ways you can add it.

Mix Into the Soil Surface

Carbon added to soil boosts water retention naturally.

Fall is the opportune time to prepare your garden for future plantings. Many gardeners pull their last crops from the ground sometime in the fall, and let their soil rest until the following spring. This empty ground makes it easy to mix in beneficial materials and prepare the ground for future plantings.

Sprinkling biochar onto the soil and gently raking it into the top few inches is an easy way to add this amendment. First, calculate the area of the space you’d like to amend. You can then weigh out the proper amount.

Recommended application rates vary depending on the soil type, but adding one to two pounds per 100 square feet is a good starting point. If you have a 10’x4’’ garden, it’s 40 square feet. Therefore, you should apply between 0.4 and 0.8 pounds of biochar.

Evenly sprinkle over the soil, then use a rake to mix it into the top few inches of the soil. It’s fine to add other amendments, like compost, at the same time.

Add Before Planting Perennials

Planting now helps new trees endure the upcoming cold.

Early to mid-fall is a great time to plant shrubs, trees, and vegetative perennials. The cooler days help the transplants avoid heat stress, and the plants have enough time to settle in before the bitter cold arrives.

If you’re planning on adding a fruit tree or new hedgerow this fall, consider adding biochar while planting. Dig an appropriately sized hole, then add a small handful of biochar before placing the plant’s rootball in the ground. Adding biologically rich compost with the biochar helps supercharge the soil with organic matter and beneficial microbes.

Once these good materials are near the plant’s roots, backfill the hole with native soil.

Add to Compost Piles

Properly mixed materials reduce clumps for smooth compost.

If you’re making compost at home, adding biochar to the pile can speed up decomposition rates and improve the quality of the finished product. Since biochar contains large particles, it improves the aeration of your compost pile. It also helps increase biological activity and retain nutrients.

One study investigated the impact of adding a small amount of biochar to an active compost pile. Results showed that the biochar helped with the breakdown of organic material and the transformation of nitrogen. Researchers estimated that adding this carbonaceous material would lead to a 20% reduction in composting time.

Furthermore, biochar decreased the amount of large lumps present in the compost. If you’ve ever tried to spread chunky compost, you know the impact of this benefit.

Adding 3% of biochar to your compost pile is enough to have an impact. If you’re not sure of the exact weight or volume of your pile, start by mixing in a few small handfuls. Try to evenly spread the biochar by turning your materials, but don’t fret if you aren’t able to achieve perfectly even distribution.

Supercharge Biochar for an Added Boost

Soaking enriches particles with nutrients and helpful microbes.

Adding plain biochar can offer numerous benefits to your soil, but infusing the material with nutrients and microbes can lead to an even bigger impact. People often refer to this process as charging. Not only does this help add other good materials to the soil, but it also helps prevent biochar from pulling nutrients from the soil after initial application.

You can charge your biochar by soaking it in compost tea, liquid fertilizer like fish hydrolysate, or tea made from worm castings. Soak the material for a few days, drain, and apply it to the soil.