Compost Gardening

Collecting Pieces for the Biochar Puzzle
By Barbara, October 26, 2009

Like a lot of other people, I want to know how to best use biochar to enhance my garden’s health and productivity. If you’ve been following the biochar story, you know the challenge: adapting a nearly miraculous soil-building method from an ancient Amazon culture to our own back yards.

Reviewing the research, it is clear that biochar (or horticultural carbon, as it’s called in some parts of the world) benefits plants as long as (1) the soil is well-enriched with organic matter and plant-available nutrients and (2) the biochar comprises no more than 30 percent of the soil mass (relevant in containers). And, although all biochar is not alike, it appears that a one-inch deep layer of coarse crumbles is about the right amount to try as a soil amendment in vegetable gardens.

As for the making of biochar, I’ll let resourceful farmers and talented engineers figure out how to do it while keeping the air as clean as possible. For my garden research needs, I’ve found plenty for free in the fire pits in a nearby campground. The tent camping area, where responsible campers routinely douse their campfires with water, offered up especially fine pickings.

Now I must design small experiments that will help answer your (and my) questions on gardening with biochar, and its link to compost. The International Biochar Initiative has published an excellent guide for doing just this. With my limited time and resources, here’s my thinking:

Pot experiments, in which biochar is mixed with potting soil to compare plant growth with and without it, are good baby steps in this type of research, so I’ll set aside some of my supply to use during seedling-starting season in spring. I grow a lot of onion seedlings and haven’t heard of much biochar work with onions, so right now they are topping my list along with eggplant, which I grow in containers all season anyway.

I’ll also do some micro-field experiments, in which I’ll compare plant growth with and without compost-activated biochar. Last year I worked with squash, but this year I’m considering peas and beans.

As shown in the photo above, I’m “activating” biochar by mixing it with moist, mature compost made from materials from my garden and kitchen. This mixture will be set aside in a cool place through the winter – its culture period, biologically speaking. By the time the biochar goes into the garden, the zillions of open nooks and crannies in the char should be well colonized by fungi and bacteria.

If plants do perform better with compost-activated biochar around their roots (and there still are many ifs), it will give us a great old/new way to make the benefits of compost last longer in soil. All this and saving the planet, too? No wonder biochar is such a hot topic.

It took us more than a year to write The Complete Compost Gardening Guide. We had many new methods to try, and what seemed like endless experiments with leaves. When we finally finished, an incredible creative team assembled by the pros at Storey Publishing turned our manuscript into the most comprehensive yet readable book on home composting ever written. Our peers agree! Last weekend we attended the 61^st Annual Garden Writers Association Symposium in Raleigh, NC, and accepted our Silver Award of Achievement in Book Writing. We feel honored to have received this vote of confidence from others who work hard to help more people have fun in their gardens!