Tuesday, March 15, 2016

Coppicing and Pollarding

My moringa trees pollarded for the new year
I recently read a great article about a concept that is new to me: coppicing and pollarding. The concept is that both are methods of pruning trees such that the wood is harvested continuously without damaging the tree. The branches are cut off at a smaller size and used for whatever they are needed for, usually firewood or crafting, like basket weaving. The only difference between the two methods is that coppicing is done at ground level while pollarding leaves a length of trunk that is topped. As far as method, I am assuming the central trunk is cut just above a junction in the first year. After that, multiple branches grow from just below the cut and those are left for several years until they are harvested. 

The more I learn about gardening, the more I realize that soil is a living thing and needs to be fed properly. Think of it like people, but with a longer metabolic cycle. While people's metabolic cycle is measured in days, soil's is measured in years. Adding synthetic fertilizer is like you eating a candy bar (well, crystal meth is probably a better comparison), where you get a quick rush and lots of energy, but then you crash afterwards. Compost is a little better, probably a little more like whole wheat bread. It is still a carb. The body uses it up, just a little slower. Wood, though, wood is the ultimate complex carbohydrate. And I don't just mean that metaphorically. Wood is actually a whole lot of sugar molecules chained together, just like starch. The only real difference is that those chains are a lot harder to break. Good chunks of wood will feed your soil for years and years. 

Coppicing and pollarding seem like a great way to get that wood. So how do you add it to the soil? Just grind it up and mix it in? Well, no. Adding sawdust directly to soil in large amounts can be deleterious to your soil. Surface area is the key. Sawdust and wood chips have a lot of surface area and mushrooms will jump in and take advantage of that, but in doing so they draw the nutrients they need to make that jump. They completely deplete the soil of available nitrogen, which is really bad for the plants.

On the other side of the spectrum, there is burying logs. A log over 8 inches in diameter can feed the soil for decades, but it won't release any nutrition at all for several years and when it does, it releases really slowly. Plus, if you don't plant it deep enough, that large chunk of wood just below the surface looks like a wall to a small plant and suddenly your plants don't have soil deep enough to meet their needs.

How I create garden beds. This one was inoculated
with king stropharia mushrooms
With coppicing and pollarding, you can generate a lot of small branches in the 1-2 inch range. Dug down into the soil, hugelkulture style, can give you soil a long burst of really good nutrition and really help build the soil web of life for 5 or more years. Plus, those branches can be used to grow mushrooms. The usual recommendation is to grow mushrooms on logs over 4 inches in diameter, but smaller logs will work if they are bundled tightly. Better yet, the branches can be inoculated and then buried once the mushrooms have taken hold, giving the gardener the ability to harvest several flushes of mushrooms from their consistently improving garden soil. 

The article mentions oak, hazel, ash, chestnut, and willow as good candidates for coppicing and pollardiing. From my experience, I can say that elm, palo verde, and elm would also be great. If you live in Arizona, scrub oak would be one of the best for coppicing. But there is a tree I have only recently been growing that I think could possibly be the best for this method: moringa. The moringa tree is an insanely fast growing tree. From a seed sprouted indoors in the spring, a moringa tree can reach 12-15 feet in height and have a trunk diameter of 2-3 inches. They are completely intolerant of frost, but in cold climates they grow fast enough to be treated as an annual. In warmer climates, if the root ball can be kept from freezing, they can die all the way back to ground level and grow back bigger each year. I have seen a tree get killed back to the ground by a 20 degree F cold snap, only to grow to over 15 feet tall and have a 3 or 4 inch trunk the next year. Plus, the pods they grow, which taste like asparagus, are only edible on new wood. If the tree is left full size, the pods that grow on old wood will be bitter. As you might imagine, any wood grown by a tree this quickly, isn't very hard. In fact, it about as soft as balsa wood. In the garden, it will probably last 2-3 years. That means that 5 trees could feed you and your garden for years to come. 

1 comment:

  1. Interesting. Of course the soft spongy soft balsa wood will break down fairly quickly. Should make for quick soil sponge.