As we saw in our column two weeks ago, proponents of sustainability appreciate biochar for its contributions to the health of our climate.

Although the science is not settled, another apparent environmental benefit is biochar’s value as a soil amendment. Gardeners should, however, do their homework before using it.

Biochar is produced from a feedstock of organic matter through a process known as pyrolysis. Possessing few nutrients of its own, biochar can improve soil due to its complex pore structure. Due to its porosity, biochar attracts and holds water as well as nutrients like nitrogen, phosphorus, and calcium. Biochar also provides habitat for helpful soil microbes and enhances drainage and aeration. By reducing irrigation and fertilizer needs, biochar conserves water, saves money, and lessens pollution risks.

Although all biochar is highly porous and carbon-rich, its specific qualities vary based on raw materials and production conditions (see tinyurl.com/2kan2j45). Also, unless left in its raw (or “straight”) form after production, biochar is enriched (“charged” or “inoculated”) with various nutrients and microbes. If local nurseries and big-box stores offer a range of products, gardeners can identify the right one for their needs by establishing their goals and then reading product labeling carefully.

Considering your aims will help with a fundamental decision, whether to use raw or enriched biochar. If your primary goal is to enhance water retention, perhaps in sandy soil, or to aerate compacted soil, raw biochar may be the right choice. However, this product can absorb available nitrogen and phosphorus during the first year after application.

If you aim above all to provide your plants with greater access to nutrients right away, then enriched biochar is the better choice — but be prudent. Because biochar is usually high-alkaline, it can improve plant health if your soil is highly acidic, but it may cause acid-loving plants to struggle. And if your soil is already alkaline, biochar would intensify that quality, leading to nutrient deficiencies and poor root development.

One can apply biochar at any time of year, though spring is ideal. And because biochar persists in the soil for centuries without breaking down, you may need to use it only once. For amounts, methods, and frequency of application, simply refer to your product’s instructions.

David Conwell belongs to the nationwide advocacy organization Citizens’ Climate Lobby and is a former member of Brunswick’s Sustainability Committee.