Bokashi is a traditional agroecological technique first developed in East Asia and now utilized extensively across Asia and Latin America. Like compost, bokashi is the product of microbial breakdown of organic matter from waste. The main components of bokashi include manure, soil, and carbon-rich agricultural byproducts, such as rice hulls and bran. Unlike compost, bokashi processing makes use of anaerobic microbial processes, in addition to those that are aerobic. These partially anaerobic conditions coupled with energy-rich organic matter allow for the accelerated breakdown of organic matter in bokashi. While composting often requires extended maturation times, frequent aeration and hydration, and large spaces, bokashi matures in approximately two weeks and is made in smaller piles for simpler management. The maturation stage of bokashi fosters beneficial microbial growth, breaks down nutrients to bioaccessible forms, and processes materials so that they no longer attract pests
Several studies support the benefits of bokashi on soil fertility and plant growth, including my own research on the efficacy and nutrient composition of different types of bokashi. In line with other studies, I have observed heightened crop growth of cucumber and kale plants and I have quantified increased amounts of ammonium—a plant-available form of nitrogen—over the bokashi maturation process (Figure 1). Moreover, I experimented with different ingredients and found no significant differences in bokashi quality made with variable starting ingredients. These findings reaffirm not only bokashi’s prowess and sustainability as a fertilizer that diverts waste streams, but also its flexibility as a product. In other words, bokashi can be made from a variety of ingredients that may be adapted to what is available and accessible, without compromising its efficacy as a fertilizer.
Here, I present best practices for making bokashi based on my research and experiences.
How to make bokashi
Step 1: Find a space — You will need to find some space that is sheltered from rain, but also well aerated to prevent buildup of smells and heat during the bokashi maturation processes. Moreover, you should have sufficient room to mix your pile. You can control the size of your piles, recognizing that larger piles retain more heat but require more effort to turn and homogenize. I have made bokashi on concrete flooring in a shed, as well as on a tarp upon a table-top in a greenhouse.
Step 2: Gather ingredients and materials — While the amounts and identities of the ingredients that go into bokashi are adjustable and may vary, the types of ingredients and process for making the fertilizer remain relatively consistent. You will need manure, carbohydrate, soil, and added microbes. Manure provides a rich source of nitrogen and phosphorus, as well as other nutrients, and you can use virtually any animal manure. Chicken manure typically contains the most nitrogen. The carbohydrate serves as a food source for the microbes that breakdown the ingredients, releasing bioavailable nutrients. Examples of carbohydrate sources include rice bran, corn flour, and potato bran, but you can experiment here!
Moreover, it is common to add dry rice hulls as a medium for microbial growth as well as to control moisture. The rice hulls can also be smoked into charcoal (similar to biochar), to further improve aeration and potentially also increase soil pH, if needed. Rice hulls may be smoked by building a simple smoker from a metal pipe with holes on the side, starting a fire inside the chimney, and surrounding the sides of the metal with rice hulls (Figure 2). Any type of soil can be used for making bokashi. The soil contains nutrients, provides a pH buffer, and gives bokashi a soil-like structure that makes it easy to apply.
Finally, you should add some sort of microbe starter culture. This starter could be baker’s yeast (Saccharomyces cerevisiae) mixed in molasses for an immediate food source, or you could collect a diverse body of indigenous microorganisms (IMOs). IMOs are collected from soil—and it is recommended you use soil from forest understory because they will likely contain a wide range of decomposing microbes, especially fungi—and then cultivated before adding as an ingredient for bokashi.
To collect and cultivate IMOs, put balls of cooked rice into a plastic bag with soil, and leave the bag opened in a warm, shaded place. Alternatively, you could bury a wooden box with rice in it under ground. After a few days, you will observe growth on the rice. It is recommended that you collect the white/yellow colonies, and avoid any blue/green growth, which could be signs of unfavorable putrefaction. Put these microbe-covered rice chunks into a glass jar with some crude sugar, shake and close the jar. After a few days, you will see liquid produced. Transfer the concoction to a pile of equal parts soil and carbohydrate, and mix the pile. Next, add just enough water to be able to make a ball of the material in your hand without too much water dripping off, but enough water to hold the ball. This technique is an approximation for about 60% moisture, and is the same to be used for adding water to the bokashi piles. Lastly, cover the pile and mix it daily for about a week. Then uncover the pile and mix it daily until it dries. Store the IMO product in an open bag and add a few handfuls to your bokashi ingredients.
Between all the ingredients you use—particularly the manure and soil—you will likely already have collected a diverse selection of microbes, but intentionally adding some will better guarantee that you have included microbes that can work in anaerobic environments. Ash, lime, and compost have also been added as ingredients in bokashi to increase soil pH or add more organic matter.
You can decide the ratio of your ingredients. I have made bokashi with an 8:3:1:1 ratio of manure to soil to bran to rice hulls, but I have also made bokashi with a 2:2:1:1 ratio of those ingredients. When deciding the ratio you want to use, consider how much of these ingredients you have available and the fact that the more manure may carry more nitrogen into your finished fertilizer. Also, you will also need a tarp, blanket, or some type of cover to keep your pile covered and promote partially anaerobic conditions.
Step 3: Combine ingredients — Combine each of your ingredients and mix to homogenize as much as possible. You may want to sieve the manure first to break it down into smaller chunks. Add just enough water to be able to make a ball of the ingredients in a tightly closed fist, without excessive water dripping from between your fingers. If it is too wet, add some more soil, bran, or other ingredients that would soak up some water. Only add water upon first combining the ingredients; do not add any more water at any other point in the bokashi maturation process.
Step 4: Turning and uncovering — Mix your bokashi pile twice in the morning (a few hours apart) for the first three days, and then mix the piles once daily for the following 10 or more days. It is important to aerate the piles so that the temperature does not exceed 60˚C and consequently selects for only thermophilic bacteria. Aerating also further homogenizes ingredients, distributes moisture, and physically breaks down bokashi ingredients. If you find that your pile is too hot, you can give it another turning. Keep the piles covered—only uncovering for mixing—for the first seven days or so, as the temperature starts to drop back down to ambient temperatures. Continue to mix the pile daily. When the pile is dry, the bokashi is complete and ready for use!
You will notice microbial growth on your bokashi, most likely after the second or third day. White growth is a good sign of thriving microbial communities. When the bokashi is ready, it should smell “earthy” and appear grayish in color. Store the bokashi in aerated bags, and keep in a cool dry place. Bokashi is best when used within a year of making.
How to use bokashi
Use approximately one handful of bokashi upon transplanting seedlings, but be sure to separate seedling roots and the nutrient-rich bokashi with a layer of soil to avoid “nutrient burn” from overwhelming the plants with high nutrient concentrations. Alternatively, you can dig a line in the ground next to plants or seedlings, fill the line with bokashi, and cap with soil. Moisture should carry the nutrients from the bokashi to the plants.
Farmers in various parts of the world laud bokashi as a low-cost, nutrient-rich, and sustainable soil amendment. I may have been the first to make bokashi in Massachusetts, as I turned steaming piles of the fertilizer in a greenhouse on a college campus in the winter, so it can be done. All you need is a few ingredients, a dry spot, and a bit of creativity.