Biochar is a soil amendment that’s been gaining popularity in recent years, and it can be very beneficial to gardens and container-grown plants. But even though biochar has been around for a while, many people aren’t quite sure what biochar is, and how to use it is even more of a mystery. But that’s why we made this beginner-friendly guide on how to make and use biochar in your garden!
Below, you’ll find everything you need to start using biochar as a soil amendment in your vegetable, herb, and flower gardens. From where to find biochar to application instructions, the tips below will cover all the details you need to master to use this organic soil additive in your landscape.
- What is biochar?
- 7 ways biochar boosts garden health
- 1. It reduces soil acidity.
- 2. It reduces the need for fertilizers.
- 3. It reduces watering needs.
- 4. It reduces plant diseases.
- 5. It reduces soil compaction.
- 6. It improves the health of contaminated soils.
- 7. It boosts the activity of beneficial microorganisms.
- 8. It enhances plant health.
- Where to buy biochar
- How to make biochar
- How to use biochar
- Frequently asked questions
What is biochar?
In very simple terms, biochar is essentially a very pure and porous form of charcoal. The product itself is a dark, fine-grained, and highly porous substance that’s either sold as a powder or in larger chunks. Larger pieces of biochar are generally crushed and broken down before they are applied to garden beds and container plants.
But how exactly is biochar formed?
Like standard charcoal, biochar is created by burning “biomass” in a hot flame. Biomass technically refers to any organic matter, including forestry (wood or plant debris) or agricultural waste (livestock feed and manure), although most biochar is made from burned wood.
However, unlike the wood that’s burned in your fireplace via the combustion process, biochar is subjected to a process known as pyrolysis. For pyrolysis to occur, biomass must be burned in an oxygen-poor environment, which results in purer and more dense carbon-rich material, also known as biochar!
7 ways biochar boosts garden health
On a larger scale, there is some evidence that biochar may be able to sequester carbon and help combat climate change. But in your garden, biochar has other benefits, including improving soil health and structure and enhancing the growth of ornamental and edible plants. And best of all, biochar is organic, so it’s perfectly safe to use in organic gardens!
Some of the main benefits of biochar include:
1. It reduces soil acidity.
Acidic soils can be difficult to grow in, and many plants struggle to thrive when soil pH levels are too low. Certain soil additives can help neutralize soil pH levels, but many of these additives need to be applied regularly to achieve lasting results. Not to mention, many of the products used for pH adjustment are not approved for organic garden use.
Biochar, however, is safe for organic gardens, and it can substantially raise soil pH levels in a single growing season. This can expand the varieties of plants that you can keep in your garden, and it may also cut down on your gardening chores as biochar doesn’t need to be applied very often.
2. It reduces the need for fertilizers.
Biochar is a highly porous substance that can trap and hold soil nutrients, limiting the amount of nutrients that are washed away when it rains or when you water your garden. When used in conjunction with organic fertilizers or compost and other soil amendments, biochar helps soils retain nutrients for longer, reducing how often you’ll need to reapply fertilizers throughout the growing season. In the long run, this results in more nutrient-rich and fertile soil that’s better for crop health, and it limits fertilizer runoff.
3. It reduces watering needs.
The porosity of biochar is useful for retaining nutrients, but it also helps lock in water, and it slows down soil evaporation rates. Even during the hot summer, you won’t need to water your garden as much if you use biochar since the soil will naturally retain water better. And while biochar will help slash your water bill no matter what, it can be particularly handy to have in sandy soils that need frequent irrigation.
4. It reduces plant diseases.
One surprising result of using biochar is that it can actually suppress plant pathogens and keep plants healthier over time. Part of this has to do with biochar’s natural fungicidal properties, but it’s also linked to the fact that biochar boosts the activity of the beneficial microbes around plant root systems. While this perk of biochar needs to be studied more, some of the plant diseases it may help combat include root rot, damping off, and brown rot.
5. It reduces soil compaction.
Compost and aged manure can be used to loosen up dense soils and help them drain better. But biochar works in a very similar manner, and it’s ideal for providing more soil aeration and encouraging plant root development. If you’ve ever struggled with heavy clay soils, biochar can help!
6. It improves the health of contaminated soils.
Biochar is negatively charged, which means it can attract and hold positively charged pollutants in soils. This has led to biochar being used in bioremediation projects, but it can also be useful on a smaller scale in your garden. However, even though biochar shows promise in this realm if you do have contaminated soils on your property, it’s best to consult with experts on how to properly remediate them.
7. It boosts the activity of beneficial microorganisms.
Beneficial microorganisms live in healthy garden soils, and they help plants absorb nutrients better, and they offer other benefits as well. Compost and aged manure can boost the activity of soil-dwelling microbes, but biochar can do this too. The porous structure of biochar creates the ideal environment for beneficial microbes to thrive, and since biochar doesn’t need to be applied very often, it can help sustain an existing population of microorganisms over time.
8. It enhances plant health.
When you look over the benefits of biochar that we’ve just covered, one thing is very clear. All of these biochar perks improve the health of plants!
Since biochar creates more fertile and well-draining soil, it supports the growth and health of plant roots. Plus, biochar moderates soil moisture levels, reduces soil compaction, and helps counteract common plant diseases. When these factors are considered as a whole, it’s clear that using biochar in your garden is a great way to grow healthier plants and gather in a larger harvest of vegetables, herbs, and flowers!
Where to buy biochar
Now that you know some of the many benefits of using biochar in your garden, you may be excited to give this soil amendment and conditioner a try. But where do you find biochar?
While biochar has been used for generations, it is only beginning to gain popularity in gardening circles, so it’s still relatively difficult to come by. You may be able to find biochar at your local garden center, but you’ll often have better luck if you look online. Companies like Wakefield and GreenGro sell bagged biochar online, and some of these products are even “preloaded” (more on that later!)
Farmer’s markets and local Facebook gardening groups can also be great places for picking up biochar in bulk, and you can often get lots of biochar at a good price if you go this route. I purchased my first bag of biochar at a local farmer’s market, and my garden has been reaping the rewards of it ever since!
How to make biochar
While you can purchase premade biochar, this product is also quite easy to make, and you can save a lot of money by making your own batch. Plus, if you make your own biochar, you can control the biomass ingredients, which can give you a higher-quality product. Just remember that different biomass materials create biochar with different compositions, so you may want to stick to wood when making your first batch of biochar.
If you’d like to make a lot of biochar, you may want to invest in a dedicated biochar kiln; however, you can also make do with a 44-gallon metal drum.
To make your own biochar, first, add dried leaves and wood to your metal drum and then light the materials on fire from the top. Allow the biomass to burn until the smoke turns a grayish-blue color, and then pile some garden soil on top of the flames and leave the lower flames to burn slowly under the soil. Once the burning materials have developed a good, dark char, put out the remaining fire in your metal drum with your garden hose and let the materials cool before harvesting your finished homemade biochar.
While this process is quite simple, keep in mind that it does involve the standard risks that always come with having an open fire. When you’re making biochar, never leave your fire unattended, and be sure to locate your biochar fire drum in an area of your property where it won’t cause any accidental fires. Also, remember to use untreated and unpainted woods to make biochar, and make sure that your metal drum is clean and free from any residues that may not be safe for garden and food use.
How to use biochar
Think of biochar as essentially a sponge in your garden. When it’s in your soil, it will draw in nutrients and water and hold them tightly; however, if you place fresh biochar in your garden, it can actually compete with your plants for nutrients and water and diminish the nutrient load in your garden for several months. This is why all fresh biochar needs to be “charged” or “loaded” before use.
You can use many different items to charge biochar, and the items you choose can enhance the usefulness of your biochar and contribute extra nutrients to your garden. Compost, manure, compost tea, worm castings, worm casting tea, autumn leaves, liquid kelp, fertilizers, and soil are all useful for charging biochar, but they have slightly different processing instructions and charging timelines.
If you purchase premade biochar, it may already be preloaded or precharged and be ready for garden use. Be sure to check the instructions on your biochar packaging to determine if you will need to preload your biochar or not. The instructions may also include details on how to apply biochar to your garden and potted plants, and these should be followed carefully.
However, if you made your own biochar, you will definitely need to charge or load the biochar before you place it in your garden.
To load biochar, first crush or pulverize your biochar chunks into pieces that are ¼” in diameter or smaller. You can use different techniques to crush biochar, but one approach is to place the biochar in a metal drum and crush it with a garden tamper. Alternatively, you can place biochar pieces in an old feed bag and crush them with a hammer, mallet, or other heavy implement.
Once your biochar is in small pieces, mix your biochar with compost, manure, or another “charging material” in a metal drum, bucket, or directly in your compost heap. How much biochar you’ll need to use can vary, but you’ll typically want to use between 10% and 50% biochar with your charging material. If you’d like, you can use just one charging material, or you can mix a few different materials together to add different plant-boosting benefits to your biochar.
After you’ve mixed your biochar and charging materials together thoroughly, keep the mixture damp and out of direct sunlight for several weeks while the biochar is “loading.” Temperatures around 70F are ideal for this process. How long your biochar will need to charge will depend on the charging materials you used, but in general:
- Biochar mixed with compost, livestock bedding, or worm castings will need to charge for 2 to 4 weeks.
- Biochar mixed directly into your compost pile will need to be turned regularly, and it will take 3 to 4 months to charge.
- Biochar mixed with liquid fertilizer, compost tea, or worm tea will need to charge for 1 to 3 days.
- Biochar mixed with garden soil will need to charge for 3 to 6 months.
After charging, biochar can be used in your garden or potted plants, but biochar is easier to apply when it’s mixed with compost or aged manure. If you blend biochar with compost or aged manure, you can apply it to your garden as a top dressing, side dressing, soil additive, or potting mix ingredient.
To use charged biochar as a top dressing, simply sprinkle a layer of biochar over your garden beds and mix it into the top 6” of your garden soil with a shovel, rake, or hoe. If you’re using biochar mixed with compost, use about 1 to 2” of the biochar and compost mix in your garden beds.
As a side dressing, sprinkle charged biochar and compost around the base of your plants throughout the growing season to give your plants an extra nutrient boost. Just be sure not to let the compost and biochar directly touch plant stems, as this can cause rot.
In potting mixes, charged biochar can be used as-is, or it can be blended with compost, and it will function as a substitute for vermiculite, perlite, or woodchips. An added benefit is that biochar is more sustainable than many of these other products, and it’s cheaper too!
If you mixed biochar directly into your garden soil when charging it, that works too, but wait at least 3 months before planting seeds or plant starts in your garden bed to allow the biochar to charge fully.
Tip: If you charged biochar with livestock bedding, make sure you allow the mixture to age for at least 3 to 6 months before placing it in your garden to allow the manure to age properly. Using fresh manure in garden beds can sometimes lead to plant tissue burn, and no one wants that!
Frequently asked questions
Biochar is made at a higher temperature than regular charcoal, and it is burned in a low-oxygen environment. This environment makes biochar a more pure form of carbon, and it also makes biochar more porous. As a result, biochar has a very large surface area, and it’s ideal for absorbing and retaining water and nutrients.
Biochar may be better at absorbing water than compost, but otherwise, it’s another valuable soil additive that works best in conjunction with compost or other organic soil additives. When mixed with compost, biochar absorbs and retains the nutrients in the finished compost. Compared to straight compost, biochar mixed with compost improves soil fertility for a longer period of time.
Yes and no. Technically, most biochar is burned wood (although it can also be burned livestock manure, burned plant debris, or other burned organic materials). However, biochar is made at a high temperature, and it is burned in a low oxygen environment, which makes biochar highly porous and absorbent and it makes it a more pure form of carbon too.
Some studies suggest that some applications of biochar may reduce earthworm populations in the short term, but biochar seemingly has no long-term implications for earthworm populations. These results depend on how much biochar is used, and lower biochar concentrations are less likely to affect earthworms. Most likely, these results were due to the fact that biochar raises soil pH levels, so it’s best to use lower concentrations of biochar if you’re worried about the health of earthworms.
Yes, as with anything, moderation is key with biochar. Too much biochar can drastically raise soil pH levels, and excess biochar may also reduce the amount of water and nutrients that your plants absorb. To avoid this, always preload biochar before use, and don’t use more than 5 to 10% biochar in the top 6” of your garden soil or in your potted plants.
One of the great things about biochar is that it remains in your garden soil for a long time. After the initial heavier application of biochar, you may not need to apply biochar again for several years. If you do want to use biochar more often, apply only light applications along with compost once a year.
Biochar is an often overlooked soil conditioner, but it can be an easy solution if you struggle with acidic or heavy soils, plant root diseases, watering issues, and more. Made of burned organic materials, biochar is rich in carbon, and it can enhance compost, aged manure, and other soil additives. Best of all, biochar remains active in gardens for a long time, so it won’t need to be applied often, and it can even be free to make!
Using biochar is one way to improve the health of your soil and grow more vigorous plants. But as any gardener knows, creating healthy soil is an ongoing process that may call for other soil amendments too. If you’d like to learn more about other organic soil amendments to use in your vegetable or flower garden, we have a full guide on that right here.