Tag Archives: soil

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!

Improving Heavy Clay Soils

Gardeners rarely begin their journey with a plot of perfect soil, but it’s something we all dream about. In the Southeast, many gardeners have to work with heavy clay soils. While clay soil is rich in minerals and many nutrients, it’s prone to compaction, doesn’t drain well in wet weather, and doesn’t hold water well during droughts. Growing certain root crops like large carrot varieties can be especially tough.

Clay soils are a great foundation to improve on. Here are a few organic methods to improve your heavy clay soil. 

Practice No-Till (or minimal-till) Agriculture

It may sound counterintuitive, but tilling can make clay soils worse. Tilling increases soil compaction and kills beneficial fungi and micro-organisms. 

Cover Crops

Cover crops add nutrients and organic matter to the soil. Great choices for improving clay soils include buckwheat, clover, and wheat. Clover has the benefit of being a nitrogen-fixing legume, meaning that through a symbiotic relationship with bacteria, it captures nitrogen from the air and adds it to the soil.

You may also want to mix in large or deep-rooted cover crops like daikon radishes, lava beans, and alfalfa. These crops help break up compacted soil and create channels for air and water as their roots decompose.

Chop & Drop

You can also use a method commonly used by permaculturalists called “chop and drop.” This method involves growing crops like comfrey, pigeon peas, moringa, sun hemp, and sorghum. These crops are chopped and dropped on the soil to decompose. Comfrey is a popular choice for this in perennial gardens and fruit tree guilds.


Broadforking your soil is a great way to loosen soil without disturbing the layers or structure. It helps mitigate compaction and preserve beneficial organisms and fungi in the soil. 

Create Permanent Beds

Even just walking on your garden soil can cause severe compaction. Creating permanent beds that you don’t till, step on, or use machinery will help make light, fluffy soil. 

Use Terraces or Swales

If your property has heavy clay soil and a slope, you’ll probably deal with water issues. Planting in rows or terraces that are perpendicular to the slope of the land will help slow down the water in your garden and reduce erosion issues. Swales built on contours take this further and are a great way to catch large amounts of rainwater, allowing your plants to access it slowly, even on significant slopes. 

Spread Compost

Finished compost is the quickest way to beef up the organic matter in your soil. Adding a couple of inches of compost to each bed adds nutrients, improves water retention and drainage, and lightens the soil.

Use Mulch

Mulch helps block weeds, hold moisture, and keep soil temperatures cool. It also adds a lot of organic matter to your soil as it decomposes. Any organic mulch can help improve your clay soils, including straw, leaves, grass clippings, woodchips, and hay. Keep in mind that hay tends to have a lot of weed seeds.

Grow Varieties Adapted to Heavy Clay Soils

Improving clay soils isn’t something that happens overnight, especially in large gardens. If you’re planting in a garden with heavy clay soils this year, try some varieties that are adapted to these conditions.

  • Chantey Red Core Carrots
    This blocky, broad-shouldered variety with a blunt tip is well-suited to growing in clay. It was introduced from France in the 1800s.
  • Danvers 126 Carrots
    These carrots taper to a blunt point and are especially suited to growing in clay soil. The strong tops aid harvesting.
  • Everona Large Green Tomatillo
    These plants produce large, tasty tomatillos and thrive even in heavy clay soil and drought.  Seed collected by Barbara Rosholdt from tomatillos planted by Mexican workers at the Everona sheep dairy near Unionville, VA. Introduced in 2008 by SESE.
  • McCormack’s Blue Dent
    This beautiful dent corn makes delicious light blue flour and is especially suited to the eastern U.S., clay soils, and drought-prone areas. Introduced in 1994 by SESE. Bred by Dr. Jeff McCormack from a cross between Hickory King and an unnamed heirloom blue dent.
  • Oxheart Carrots
    A good carrot choice for shallow or heavy clay soils that most carrots don’t like. Dating to 1884, this variety produces thick, sweet “oxheart”-shaped carrots, 5-6 in. long and 3-4 in. wide, weighing up to a pound!
  • Pike Muskmelon
    Bred specially for growing in unirrigated clay soil, this vigorous melon has outstanding flavor and good disease-resistant. Introduced in 1935, Aaron Pike of Pike & Young Seeds; seedstock supplied to SESE by Aaron Pike’s niece.
  • Tennessee Red Valencia Peanuts
    This pre-1930 produces rich, sweet peanuts with red skins. It’s easy to grow without hilling, even in clay soils.
  • Texas Gourdseed Corn
    Originally brought to south Texas by German farmers who migrated from Appalachia during the late 19th century, this variety withstands drought and does well in clay soil. In south Texas, this is considered to be the best choice for tortilla flour.
  • Turga Parsnip
    This Hungarian heirloom produces short, stout roots that are good for heavy clay soils.
  • Southern Peas (Cowpeas)
    These productive peas are well-adapted to poor soils and drought. We carry 16 varieties at SESE.

10 Easy Ways to Improve Your Soil

Want healthy plants? Start by building healthy soil. Your soil health can affect your plant’s productivity, disease and pest resistance, and more. Use these ten strategies to improve your soil and build a healthier, more productive garden.

1. Start composting.

Compost enriches the soil and adds structure and beneficial fungi and bacteria. It’s an excellent amendment for any garden and easy to make yourself. Check out our post, Black Gold: Making Compost, for easy directions to get started in your backyard.

Those without yards can consider vermicomposting or check with community gardens or city compost facilities to bring kitchen scraps to and access aged compost.

2. Grow cover crops.

Cover crops are not just for big farms! Cover crops help improve the soil in many ways. Some are “nitrogen fixers” like clover and vetch and add nitrogen to the soil as they grow; other crops like buckwheat help quickly build up organic matter and make excellent mulch.

All cover crops are a good way to cover the soil. They shade it holding in moisture, provide habitat for beneficial insects and pollinators, and their roots hold the soil preventing erosion.

You can read more about using cover crops in your garden here.

3. Get a soil test.

Testing your soil can help you make the best choices for your garden, saving you time and money. You’ll learn what nutrients may be missing and whether you should amend your soil’s pH. Check out Understanding Soil Tests for a more in-depth explanation.

You can purchase at-home soil tests at most garden centers or send your soil to be tested. Many universities and state and county extension services offer very affordable soil testing.

4. Understand the soil food web.

The soil food web is similar to a “food chain” but is non-linear. It’s made up of plants, animals, and all the organisms in the soil from visible insects and fungus to microscopic bacteria. A healthy soil food web is key to a healthy garden and ecosystem. Learn more by reading our post, The Soil Food Web.

5. Reduce erosion.

Not everyone is blessed with a large, perfectly flat garden site. Even if you are, wind can still wreak havoc on exposed soil. Don’t lose soil to the effects of wind and water.

If you live in a windy area, utilize windbreaks. These can be fencing, shrubs, or trees. Even young shrubs and trees can make a surprising difference.

To prevent water erosion, you should try to keep your soil covered. Use cover crops whenever possible and keep the soil around plants mulched. Permanent pathways with a cover crop like clover are ideal.

If your property is sloped, look into permaculture methods like planting on contour and building swales. These can help you stop erosion and collect water for your plants!

6. Provide habitat for beneficial insects.

When people hear beneficial insects, they often think of bees, butterflies, and other pollinators. While you should strive to help these species, there are many more that also play key roles in keeping your garden healthy. These include many predatory species such as wasps, beetles, and mantises.

You can support beneficial insects in many ways. Using cover crops and mulch, as I mentioned above, helps provide habitat as does planting native species and leaving dead material in your garden (unless it has a pest or disease issue). You can also create your own habitat by building an insect hotel.  Of course, it’s also important to avoid using pesticides. Even organic pesticides can spell doom for beneficial insects as they usually affect more than one species. 

7. Use mulch.

I’ve mentioned mulch a couple of times now, but it’s incredibly helpful in the garden. It helps to block weeds, keep the soil cool and moist (or warm in the winter), and provides structure and organic matter as it breaks down.

Check our post, Mulch Ado…, to learn more about why mulch is important and how we use it at SESE.

8. Rotate your crops.

Whether you have an acre in garden or just a tiny little plot, you should rotate your crops. Rotating crops prevents pests and diseases from building up the soil where you grow a particular plant. It also helps to reduce nutrient depletion. One year you grow heavy feeders like tomatoes or corn, and the next, you grow nitrogen fixers like beans and peas or a cover crop.

Need advice? See Planning Crop Rotation by Plant Family.

9. Amend your soil.

As you’ll learn from your soil test, it is sometimes necessary to add amendments to your soil. These amendments can be used to change the soil’s pH like lime, wood ash, or peat moss. Other amendments allow you to add the macro and micronutrients that are necessary for plant growth. These include manure, compost, eggshells, greensand, and fertilizer.

Learn more about amendments and common nutrient deficiencies in plants here.

10. Reduce or eliminate tilling.

Rototilling may seem like a crucial part of gardening, but many farmers, gardeners, and scientists have discovered that it’s possible to grow a more productive and more environmentally friendly garden by ditching the tiller.

Going no-till reduces compaction and keeps the soil structure intact. It allows you to use plant and cover crop residue as mulch that will decompose as it would in a natural ecosystem. It also allows beneficial bacteria, insects, and fungi to thrive in the soil. 

Follow these tips to build healthy soil in your garden.