Biochar-based potting soil recipe

This is the second of two articles about biochar, the term for charcoal when it is used as a soil amendment. For the first article, detailing the author’s involvement in an on-farm study of biochar from the October 2017 GFM, click here.

This article will cover the method for making charcoal that I settled on, providing you with an easy, low cost, low-tech way to turn your burn pile into a long-term asset. But before that I’m going to quickly describe how charcoal relates to the carbon cycle, our current carbon crisis and how charcoal can improve forest health.

The impacts of climate chaos on Astarte Farm have forced us to look for solutions that provide increased long-term resilience in our soil systems, and biochar has shown good promise in moving us toward that goal. Biochar is a paradoxical substance. It is both an ancient agricultural practice developed thousands of years ago in the Amazonian Basin, and at the same time a relatively new approach to enhancing and stabilizing soil fertility.

While it is inert on its own, it becomes a haven for a complex of microbiology. It is not a fertilizer, but freely absorbs and releases plant nutrients as needed. While is has a dry, almost crystalline appearance when freshly made, it readily absorbs water and releases it when needed. It is important to start with a high-quality biochar, but to be truly effective it is equally important how you use it, and how you prepare it in advance for use.

There is, with all of us, a lens through which we see the world. And while each of ours is different—informed by our past, by our present, where we have come from—a common lens we can all share is the recognition that our globe is changing.

While climate change receives increased amounts of attention by global leaders, there is still a lack of intention placed on one of our greatest questions—how will we feed ourselves with increasingly unpredictable weather patterns? Global predictions on staple crops are that by 2050, climate change could cause irrigated wheat yields in developing countries to drop by 13%, and irrigated rice could fall by 15%. In Africa, maize yields could drop by 10–20% over the same time frame.

Charcoal is a naturally occurring form of carbon. Charcoal is a byproduct of burned ecosystems such as forests and prairies that captures the carbon in plant matter and preserves it in a form that can stay in the soil for between several hundred and 10,000 years. Known as recalcitrant carbon, charcoal captures organic matter in its pores, creating areas of “concentrated labile carbon,” which is the most accessible form of carbon for the microbial community. In addition, charcoal can capture nutrients and water, supplying a broad array of fertility needs for plants. Biochar is what charcoal is called when used for agricultural purposes.

This year, I was offered a contract by an established essential oil/tincture company to grow hemp for them. And I happen to have a field that has grown vegetables in the past but wasn’t growing anything this year. So I figured, why not, and applied and got a license.

I was going to rely on my experience growing a wide variety of vegetables and flowers to figure out how to grow this new (to me) crop. But then I remembered that Concentrates Incorporated, organic agriculture specialists in Oregon, has experience consulting on many different crops, including cannabis, hailing as they are from one of the first states to legalize the many forms of cannabis. Read on for their advice on how to have a great hemp crop.

The modern age could very well be termed the age of carbon. We have increased the amount of carbon dioxide (CO2) in the atmosphere by more than a third since the Industrial Revolution began. A gas that keeps heat from the sun contained within the earth’s atmosphere, CO2 makes up more than three-quarters of the greenhouse gas emissions in the world. At the same time agriculture is currently experiencing a carbon crisis, with 50-70% of the world’s carbon in farmland soils off-gassed into the atmosphere due to tillage. Carbon is the single most essential element in soil fertility as it aids soil structure development, water retention, nutrient retention, and biological processes.

High tunnels have played a crucial role in season extension for market growers, with popularity increasing over the last decade to meet demand for locally grown produce year round (or close to it). Once built, the high tunnel becomes some of the most valuable real estate on the farm and many growers are able to produce exceptional yields in the first few years. After several seasons, yields begin to decline and many growers struggle to maintain productivity.

High tunnels are valuable real estate on a farm, but growing under cover long-term can result in nutrient imbalances and pH changes in the soil that impact yields. Phosphorus, calcium and magnesium build up over time and interfere with other nutrient uptake. High pH irrigation water and fertilizers cause soil pH to rise, limiting micronutrient availability.

There are many types of clover used to discourage weeds, add nitrogen and biomass to the soil, and prevent erosion. In addition, clovers attract beneficial insects and reduce aphids. The main uses for clovers are: as overwinter cover crops; green fallow (full-year cover crops); undersown in existing food crops; and no-till or reduced-till crop sowings in standing clover. I’ll talk about each of the uses we have tried, and look at the various types of clover and their requirements.

Adding fertility to the farm comes in many forms: cover cropping, composting, and spreading of a variety of powders, pellets and potions.  To me, cover cropping and composting help address the greater fertility needs and long-term productivity of the soil. Spreading of certain minerals, such as lime, contribute to this same broad approach as well, and the combination of these practices forms the basis of a healthy soil where crops can thrive. In addition, there are the amendments that I add to specifically boost the following crop, including high nitrogen byproducts like blood meal and feather meal, and mined minerals like sulfate of potash. These are typically relatively concentrated (for organic) materials, chosen for specific known deficiencies.

Have you ever lost precious seedlings in your greenhouse to frost? How about tossing a flat or two out due to heat stress or a missed watering? Or better still, stared at a tray of seeds that won’t germinate, with smoke coming out of your ears, because you’re sure someone (not you!) mis-watered them at a critical moment? Have you ever shrugged to yourself reading the growing instructions on a seed packet that says “Germinates best at 70 Fahrenheit” while standing in your 85-90 degree greenhouse? You’ve started to look into a germination chamber to solve some of these issues, but they look pricey and have limitations like not being able to handle as many flats as you’d like to start at once.

Microgreens are becoming a more common ingredient in all kinds of cooking. Someone has to supply all those micros I see garnishing dishes in restaurants, sprinkled in salads and even being sold at farmers markets. The mainstreaming of microgreens has expanded a market that local growers can sell into year-round with minimal heated space. A commercial amount can even be produced indoors under lights.

Plant diseases present significant challenges for vegetable growers. They can be difficult to diagnose and hard to control, and have significant impacts on quality and yields. Seed-borne diseases are especially challenging, because the earlier in the plant’s lifecycle the pathogen comes in contact with the crop, the greater the potential for serious disease problems to develop.

January is the best month to choose crops, order seeds, and plan your seed-starting and planting schedules. Spring is still months away, but you can start planting earlier than ever before with the new season extension products available from Johnny’s. And by doing your planning this early, you can be sure you won’t miss any important windows for valuable early crops.