Chipped Branch Wood
CHIPPED BRANCH WOOD (CBW)
By Master Gardeners Bernadette Nouel and Tommie Smith
Contributors: Master Gardeners Debbie Platt, Guma and Janet Thorp
What is Chipped Branch Wood (CBW)?
Chipped Branch Wood (CBW)—also called Ramial Chipped Wood (RCW or, in French, "bois raméal fragmenté")—is a concept developed in the mid-1970s by a team of researchers in Quebec. What began as a search for ways to use waste products from the forestry industry led to a deeper understanding of how the rich soil of the forest floor is created, and how this process can work for farmers and home gardeners. In a forest ecosystem, plant tissues are quickly transformed into nutrients by soil microorganisms. What the researchers learned is that twigs less than three inches at the tips of deciduous tree branches contain soluble lignin, the base for soil aggregates which creates a long-lasting humus, regenerating and reactivating the soil structure. When this wood decomposes, the nutrients are released into the soil and become available to plants.
This technique was developed and studied by the Laval University, Wood and Forestry Science in Quebec under Gilles Lemieux. The scientific journals were written in French and, as a result, CBW was primarily tested in France. It’s now a widespread practice in Canada, Europe, Africa and other parts of the planet. Sonoma County Master Gardener Bernadette Nouel had used this soil-building technique in the Jardin Bourian in the southwest of France from 2000 with successful results.
The Food Specialist Group of the UC Master Gardener Program of Sonoma County decided to conduct our own experiment in Master Gardener Tommie Smith’s food garden in Cloverdale. Seven Master Gardeners, led by Bernadette Nouel, began our experiment on November 3, 2015.
CBW is created by chipping young branches of hardwood trees no larger than three inches in diameter in the fall or early winter when all the nutrients of the tree are stored in the buds on these small, flexible branches. We began by gathering small branches with green leaves and twigs with buds from a large oak tree.
The branches were run through a chipper/shredder to reduce the size so that more surface area is exposed to the soil microorganisms in order to hasten decomposition.
We spread a 4 by 8-foot garden bed with the Chipped Branch Wood to a depth of four inches. We prepared a control garden bed of the same dimensions with finished compost. In both beds, the material was laid on top of the soil with no tilling or disturbing of the soil.
We then sowed one row of fava bean seeds down the center of each bed and sowed a row of peas on each side of the favas. The peas will use the fava beans as support structures as they grow.
Because our tree had not yet dropped its leaves for the winter, we had a high percentage of green leaf material in our CBW. We intend to repeat this experiment in early January 2016 when there will be bare twigs with larger buds on the tree. We also plan to incorporate twigs from nearby madrone trees, which are hardwood but not deciduous. It will be interesting to compare the three garden beds over time: one bed prepared in November with lots of green leaves and small buds; one bed prepared in January with no leaves and larger buds from the oak tree with the addition of some madrone twigs; and one non-CBW control bed with only compost. In spring, each bed will have identical plantings for accurate comparison.
What Happens Next?
Over the next year through the different growing seasons, we will post periodic reports of our observations and any measurable differences between the beds.
We will observe:
1. Water use. If, as we expect, CBW is a technique that saves water—it will be a timely experiment for Sonoma County and other California gardeners.
2. Plant response. We will be feeding the soil without fertilizer or pesticide and expect improved soil structure and increased soil fungi. While we don’t have laboratories to conduct precise measurements, we hope to observe a) stronger, healthier plants, b) increased beneficial soil organisms (e.g., threads of mycelia) and c) increased vegetable production.
Photos: Tommie Smith