Tag Archives: soil building

Biochar 101

Spend enough time reading about sustainable agriculture, and you’ll inevitably run into the word biochar. In recent years it has seen a surge in popularity and is often touted as an amazing, organic garden amendment. But what is biochar, and is it great for the garden? Today, we’ll dig into what biochar is, what it does to soil, how it’s made, and how indigenous farmers have utilized it for thousands of years.

What is Biochar?

Biochar is a type of charcoal made from biomass or plant material that has been burned or decomposed in a controlled, hot, low-oxygen process called pyrolysis. 

In other words, wood chips, leaf litter, twigs, dead plants, or other similar materials are burned in a container that allows very little oxygen to enter. This process produces little to no contaminating fumes.

Biochar is lightweight, highly porous, and has a large surface area. Biochar is approximately 70 percent carbon but contains nitrogen, hydrogen, and oxygen, among other elements depending on the materials. Its exact composition depends on the plant material and temperature and the time it was processed. The University of Tennessee Extension Service has some wonderful charts on Biochar effects and macronutrient contents.

The Benefits of Biochar

You can use biochar as a soil amendment or conditioner in your garden soil or containers. Biochar proponents recommend biochar for its benefits in the garden and the larger environment.

Biochar’s Soil Benefits

  • Biochar may increase cation exchange capacity (CEC), a measure of the soil’s ability to hold positively charged ions. CEC influences soil structure, nutrient availability, soil pH, and soil’s reaction to fertilizer and other amendments. 
  • Biochar may enhance water-holding capacity.
  • Biochar may increase soil surface area. 
  • Biochar may increase plant nutrient availability.
  • Biochar increases soil pH.

Biochar’s Environmental Benefits

  • Biochar sequesters carbon in the soil.
  • Biochar may increase agricultural productivity.
  • Biochar may help improve soil water filtration.

Biochar Origins: The Amazon Basin

Agriculture is one sphere where some of the greatest minds, particularly those of BIPOC folks, have never gotten the credit they deserve. Biochar is likely one of those cases.

When the Portuguese first began to explore and colonize the Amazon Basin, they were surprised to find sections of dark rich soils surrounded by common, less fertile Amazonian soil. They called these soils terra preta de índio or “Indians’ black earth.”

Unsurprisingly, Europeans did not immediately attribute these high-quality soils to the work of indigenous farmers. Instead, many Europeans thought they resulted from natural causes such as ash fall from Andean volcanoes or sediment from long-ago lakes and ponds.

Today, the content of these soils, which commonly includes tiny pottery shards, fishbones, and other residues from cooking and habitat, tells us otherwise. The indigenous peoples that called these lands home undoubtedly improved these soils with biochar and other amendments, probably beginning between 450 BCE and 950 CE. Through carefully crafted management, once-infertile soils had been made suitable for large-scale agriculture. 

Sadly, the descendants of these careful farmers were forced to give up their more agrarian lifestyles, probably in the 16th and 17th centuries, as they faced the effects of colonization. The peoples of this region were hard hit by introduced European diseases and violence, including Bandeirante slave-raiding.

To escape colonization, many likely took up a more nomadic lifestyle. Slash-and-char style agriculture may have been an adaptation of older farming techniques to cope with their migratory lifestyle. 

Each year, the soils in the Amazon basin are exposed to warm tropical temperatures and about 80 inches of rainfall. The fact that these incredible soils still exist today, after about 500 years, is a testament to the power and knowledge of indigenous farmers. 

A hand holding a piece of biochar in front of a barrel full of it
Homemade biochar

Making Biochar

Today, you can purchase biochar, but with a little time and effort, you can also make your own.

One of the simplest methods for making biochar is to do it right in the garden. Dig a trench in your garden bed and fill it with brush and plant material. Light this material on fire, and once it’s burning well, cover it with an inch or so of soil to reduce the available oxygen. This method is easy but also the least efficient way.

A slightly more efficient method is to place your material in some sort of closed container in a fire. You can do this with an old metal barrel, pot, or pan. Place your material in your container, then build a fire beneath and around the container to heat it.

Pyrolysis equipment is the most efficient route and is available for those who would like to produce large-scale or commercial biochar. Biochar.co.uk has some great information and resources for any level of biochar production you may be interested in. 

If you run a wood stove in winter, Edible Acres, a permaculture-focused Youtube Channel, also has an excellent video on experimenting with making biochar in a wood stove. 

Please check your local laws and regulations before doing any burning. Stay safe, always watch your fires, and always have a good water source immediately at hand.

Biochar can be a great way to improve your soils without paying for expensive truckloads of topsoil, fertilizer, or other amendments. Its properties and benefits may vary with each batch of biochar and the garden you use it in. Let us know in the comments if you’ve had success with biochar!

Can I Use Manure On My Garden?

An abundant source of manure can seem like garden gold, especially for those moving away from commercial fertilizers. Manure provides important nutrients, improves texture, and increases soils’ water-holding capacity. However, like anything else in gardening, manure isn’t always a perfect solution. Here are a few things you should know if you’re considering using manure on your garden.

Using Manure Properly

Manure may be full of nutrients, but it can also contain bacteria. Some of the bacteria in manure can be transmitted to humans via vegetables if it’s not properly handled and applied to the garden. While many small gardeners feel perfectly safe using manure, especially from their own livestock, you should still generally avoid using fresh manure around crops that may come into contact with the soil.

If you’re looking for good guidelines, the USDA National Organic Program has standards for handling fresh manure. These are especially important if you sell or hope to sell some of your produce.

USDA National Organic Program (NOP) Standards

The NOP has specific rules for when growers may apply non-composted manure to their gardens.

If you’re using manure on crops with an edible portion that may come into contact with the soil, you must apply the fresh manure 120 days before harvest. This rule includes vegetables that come into direct contact with the soil, like carrots and melons, and those that may come into contact with it from irrigation or rain splash, including leafy greens, peas, and beans.

Fresh manure can be incorporated into the soil up to 90 days before harvest for crops that don’t have an edible portion that touches the soil, like tree fruits and sweet corn.

Note that the 90- and 120-day restrictions apply only to food crops; they do not apply to fiber crops, cover crops, or crops used as livestock feed.

Avoid Run-Off

When applying fresh manure to gardens, you also want to avoid run-off. Manure running into local streams, storm drains, and other waterways can lead to excessive amounts of nitrogen and other nutrients in the water, which may cause toxic algal blooms. To help prevent and control run-off, you can plant cover crops, better incorporate the manure into the soil, and create berms or swales.

Composting Manure

Alternatively, you can compost your manure. To kill bacteria and pathogens in compost, you’ll need reasonably high composting temperatures, between 131-170°F (54-60°C), for several days. These temperatures will also kill parasites, weed seeds, and harmful fungi.

Herbicide Contaminated Manure

The widespread use of commercial herbicides has also presented another issue for gardeners. Manure from animals that have eaten hay or forage from fields that were treated with aminopyralid or related herbicides like clopyralid or picloram may be contaminated. Animals’ digestive systems do not filter these chemicals out. Therefore, adding their manure to gardens can severely damage legumes like beans and peas, solanaceous crops like tomatoes and peppers, and other broadleaf crops. You can check for herbicide residues at home with a bioassay test.

Seedlings (manure post)Bioassay Test

You’ll need 6 to 10 pots and seeds or seedlings to conduct a bioassay test. In its simplest form, you will check and see how seedlings grow in soil you know to be safe compared with how seedlings grow in soil mixed with the unknown manure.

Fill half of the pots with soil you know is good quality and free from herbicides, like soil from your own garden. Fill the other half of the pots with a one-to-one mixture of soil and manure. When you collect manure for this, take samples from different areas and depths in the pile and mix them together.

Then plant the same type of seed or transplant the same age and type of seedling in each pot. Observe their growth over the next three weeks. Make notes on the plant’s overall growth, including the leaves and roots. Watch for signs of stunted growth, discoloration, abnormal growth, curled leaves, root swelling, or stunting.

The North Carolina Extension Agency has further instructions for Bioassay tests and a helpful table covering some recommended bioassay species for residual herbicides and the expected injury symptoms.

Can I Use Pet Waste?

No, you should not use pet waste in the garden or compost it for use in the garden. Waste from cats and dogs may contain heavy metals, bacteria like E. Coli and Salmonella, as well as parasites like tapeworms and ringworms. 

If you need to get rid of pet waste, make a separate compost pile, and don’t use it on the garden.

If you have a pet rabbit, their waste is safe for the garden as long as you use compostable litter.

Can I Use Human Waste?

It sounds weird, as most of us in the United States have modern plumbing, but the idea of using human waste on crops isn’t new. Until about 400 years ago, adding human waste back to the soil was commonplace.

Today, this practice is mostly followed by off-grid and sustainability enthusiasts. If you’re interested in these topics, you may have heard of “The Humane Handbook,” written by Joseph Jenkins in 1995, which helped to make waste composting systems more popular.

If properly managed, human waste can be safely composted and used. That said, you’ll need to be set up for it. Even then, you should only use human waste when it’s fully composted and only use it around fruit trees and ornamental plantings.

Manure is a wonderful garden amendment when handled properly. If you want to use manure in your garden, follow these steps to ensure it doesn’t contaminate your garden with herbicides or bacteria.

Getting a Soil Test

Soil tests are a simple and accurate way to learn more about your garden soil and determine what amendments it needs. A detailed soil test, a little research, and an understanding of the results can drastically improve your yields and eliminate recurring issues in your garden.

Where to Get Soil Tested?

There are a few ways you can get a soil test. While you may find simple home test kits at your local hardware store, these generally aren’t as accurate or detailed as a professional test. 

Typically, you can get your soil tested through your county extension agency or agricultural college. Many extension agencies and state colleges offer residents free or cheap soil testing. They typically include some recommendations if amendments are needed. Private labs also provide these services, but they may not be as affordable for home gardeners as the other options.

How to Find Your County Extension

To find your county extension agency try browsing the listings of Pick Your Own. They list contact information for county extension agencies across the United States.

When to Sample

We recommend having your garden soil tested every one to two years. Orchard areas typically only need to be tested every three years.

Late summer and fall are ideal times to collect soil samples. This time of year will represent how the soil’s nutrient status affects crops. If needed, you can take soil samples in spring, but you should avoid collecting frozen or waterlogged samples as they may not mix well.

Don’t collect soil after adding lime or other amendments. It’s best to wait several months or even longer if the weather is dry until they’ve dispersed into the soil.

Depending on the lab you’re working with, and how busy they are, it may take several weeks to get the results from your sample. It’s best to send them in well before you need the results.

Where to Sample

You want to get a good picture of the soil throughout your garden, not just in one spot. To do this, you’ll create a composite sample to send in, made from samples taken throughout the garden. For small-scale home gardens, five to eight samples are generally adequate. 

If your garden appears to have distinct slopes and soil types, be sure to get a sample from each area. Avoid taking samples from sites that don’t represent your garden well. These may include garden edges and unique wet spots.

How to Take a Soil Sample

Take soil samples using a spade or auger and collect them in a clean container. How deep you should sample depends on your garden type. Aim for small uniform cores or thin slices starting at the soil surface. 

For traditional backyard gardens, sample to the tillage depth. For no-till gardens, take one sample from the top 1 inch of soil and then take a second sample from the same spot at a depth of one to six inches.

For areas you’d like to establish an orchard, take a surface sample from zero to six inches deep and a subsoil sample from six to twelve inches deep. In established orchards, scrape aside plants and organic matter and take a surface sample. 

Once you’ve collected your samples, gently crush them and remove any stones and roots. Then allow your soil sample to air dry. Spread it out on a clean surface in a shady spot and make sure it dries before mailing. Don’t heat your soil to dry it.

Your samples should be at least one cup of soil in a plastic bag. Depending on the agency or lab, they may have you use or provide a specific bag. Follow your extension agency or lab’s instructions for sending your sample. Be sure to include all necessary paperwork and your name and address. 


The gardening science can sometimes feel intimidating, but it doesn’t have to! Getting your soil tested is a simple way to learn how to amend and improve your soil correctly. Your soil test and advice from the local extension agency can help you build healthy soil and grow healthier, more productive plants.