We’ve been given a gift at the VegHeadz garden, and we don’t quite know what to do with it. This year Leon County became the first county in the nation to convert yard debris into biochar, a carbon-negative material, in an effort to reduce carbon emissions. See our
previous post and references with more information about what it is, why it is beneficial, and how it is produced.
We have a big bag of the biochar and we need to learn how to use it. It is confusing since most gardeners are just becoming aware of this soil amendment and there is much conflicting and complicated information available from gardening sites, producers, and research reports. Research about use in small gardens is still sparse, with little consensus, standards, or repeatability across the biochar spectrum.
Most sources agree that the addition of untreated biochar to the soil may temporarily immobilize nutrients, potentially leading to a short-term reduction in plant growth. Avoiding this result would require several months up to a year of fallow time after application of untreated biochar to allow the soil and its organisms to stabilize before planting.
After poring through a lot of online information about biochar, it seems that all the discussion about how it is made and what it is made of isn’t as important to a gardener as how it is treated prior to applying to the soil. The purpose of treating the biochar, called activating, or inoculating, or charging, is to fill the nutrient storage capacity of the biochar and pre-load it with microorganisms so it will cause the least disruption in the growing medium, and will immediately begin doing it’s work in your soil and providing nutrients to your plants.
There are a number of approaches for the home gardener to charge or activate biochar.
Charging with Compost—This seems to be the easiest method if you have compost available, although it takes longer. It involves adding biochar in any amount up to a 1:1 ratio to existing compost and allowing it to “marinate” for four to six weeks. Some sources recommend soaking the biochar in water before mixing it with the compost to help nutrients move through the material easier. It’s also important to keep the compost/biochar mix quite wet during the charging period. This should allow time for microorganisms and nutrients to inhabit the many pores in the biochar particles, and for these processes to become stable. This can be scheduled so that it is ready when it is time to apply compost before planting, reducing or eliminating any fallow time.
The same thing can be accomplished over a longer period by adding biochar to your nitrogen and carbon materials when you are feeding your compost bin. In this way, the nutrients and microorganisms that are created in the composting process will inhabit the biochar at the same time.
According to the University of Arizona Extension, “Biochar lacks nutrients like nitrogen and phosphorous so mixing it with compost or manure is a helpful option. Biochar has the ability to absorb these nutrients and keep them in the soil longer and is better than using compost alone. Mixing up to 1 part compost with 1 part biochar is effective at increasing the time nutrients stay in the soil, but most gardeners start with ratios closer to 10 parts of compost to 1 part biochar to be sure that plants tolerate it well. Before adding this mixture to soils, or using it in a potting mix, it should be aged for several weeks under moist conditions to allow for the exchange of nutrients between the two materials. This will also help microorganisms, worms, etc., found in compost to adjust to the biochar. This step also helps beneficial fungi that grow on plant roots to develop quickly once the biochar-compost mix is applied to soil.”
Charging with liquid— This is a method which produces quicker results and biochar that can be applied sooner than the compost charging method. This method follows a common pattern—add nutrients, add liquid and let it sit. Some proponents of this method claim that aeration of the liquid mixture is essential for the flourishing of the microorganisms we want in the biochar. This makes it similar to the method for creating bio-brew from compost or animal manure with biochar added to the mix. Look for Bio-brew under Garden Resources in the left sidebar for details on this method. A drawback is the inability to do this in larger amounts without multiple batches, and it requires an aeration device such as a fish tank pump.
If aeration is not used, the biochar can be activated by mixing in some source of nutrients, and letting it sit for approximately three days before adding it to your soil. The liquid is usually water, and the source of nutrients can be organic or conventional fertilizer, compost, manure, worm castings, etc.
The llquid method will also furnish microorganisms to a greater or lesser degree, depending on the nutrient-supplying material used, but the short soaking period may not allow the microorganisms to develop to the same extent as the compost method, and access to oxygen is necessary for microorganisms to proliferate. Also, using this method to activate biochar in any substantial volume would be cumbersome for a home garden.
Our goal at the VegHeadz garden is to run our own informal trial by planting some of the same plants in soil that does not include biochar, in soil with biochar added without charging, in soil amended with biochar charged with compost, and in soil amended with biochar charged with the liquid method. We plan to do the compost charge in one bay of our four-bay compost bins to have it ready to apply in preparation for our spring planting season. Any differences in pests and diseases, and plant health and growth, will be noted.
Several gardeners have also taken small amounts home to try in their own gardens. MG Dave Skinner has a green house and tropical plants to protect. He soaked the biochar overnight with commercial liquid fertilizer, combined it with his potting mix, and applied it to his greenhouse plants. He reports that so far they look healthy with no adverse effects. He also added biochar to his compost bin to charge there and will use it on his spring garden.
We have several concerns or questions.
According to some sources, biochar tends to increase soil pH, and our soil test results reflect we are already operating at the high end of the desirable pH range. Other sources indicate that while biochar can indeed raise pH if it is extremely LOW such as 5.0 or below, if the pH is close to neutral or alkaline it does not further raise the pH. This would tend to support the claim by some sources that biochar regulates pH. We had our soils tested this fall so we have a benchmark with which to compare biochar amended soils. This is highly recommended when adding amendments to your soil. We have had some variable results when sending samples to different labs and one of our gardeners who uses a probe-type pH meter at home has additional input. More about this in a future post.
Second, in general, biochar seems to be more beneficial for sandy or poor, nutrient-depleted or acidic soils than healthy ones. Our soils are already healthy, and definitely not acidic, so our main purpose in using biochar would be to utilize its water and nutrient retention and microbe boosting capabilities, and its ability to sequester carbon and some soil-borne pathogens over long periods of time—to do our bit for the environment.
A third consideration is whether biochar can help remediate the copper concentration in our garden soil. Biochar is reported to be effective in sequestering copper contamination in soil. Our recent soil test indicated that our soil contains much more copper than recommended. It has been determined that it is probably from the use of animal manures in the garden mixes that we have applied, which is further concentrated by composting plant material from our garden that has been grown in the high cooper soil. Copper is included in the feed for most domestic animals because of its antimicrobial qualities as well as for nutrition. The buildup of this element in our soil has affected seed germination and plant growth to some extent and could get worse as copper levels continue to rise. For this reason, we will not be using manure to provide nutrients in our liquid activation of biochar.
Finally, it is important to proceed carefully when adding any amendment to your soil, and particularly with biochar because once it’s there, it cannot be removed and it will not degrade naturally in our lifetime.
Several sources with information about liquid activation of biochar.
