Thursday, January 06, 2011

Permaculture ideas : A help or a hindrance ?

Permaculture is a design system.  It involves looking at nature and seeing what works and how it works and then applying some of that inherent wisdom to how we design our own food production systems.  One connects things, juxtaposes them, and then basks in their productive symbiosis, two for the price of one.

To the north of our potager (vegetable plot) we have our willow plantation, several rows of thirty two different varieties which, along with providing bees with an early and continuing source of nectar and rods for living willow structures, acts as a windbreak to our veggies from the cold dry winds that blow from the north.  To the east, we have a couple of black locust / false acacia (robinia pseudoacacia) trees, which were principally planted to obscure the slabby grey wall of our neighbour’s house.

Both of these trees could be classified as pioneer trees—trees that move in first to untended ground, the first step towards natural reforestation—and are very competitive.  They chuck out energetic roots that go hunting for nutrients and water. Serge, our helpful neighbour, has delivered us another load of chestnut planking that he has torn out of a building renovation and rescued from the site bonfire.  This meant that I was able to enclose another four raised beds in the potager and in all the preparatory digging and clearing of the pathways, I discovered some roots.

N-fixing nodules on false acacia roots
Blooming scary, great long, strong ropes of roots, thick as a man’s wrist (well, finger, I exaggerate!) and running a long way into the vegetable growing area.  One of the disadvantages of raised beds is that they dry out quicker and last summer was exceptionally dry, so to have tree roots pumping out what’s left of the precious humidity that remains isn’t desirable.  But wait.  The roots of false acacia are nitrogen fixing, feeding other plants … hmm.  It’s a legume, so the roots have nodules (see photo) containing nitrogen-fixing nitrogen bacteria. 

how far the roots stretched
So, the permaculture questions:  do the vegetables gain more from the windbreak effect than the water they lose to thirsty willow roots? and do they gain more from nitrogen fixation than they lose from thirsty false acacia roots?  In short, I don’t know but it’s an interesting conundrum.  Practically, we plan to progressively remove the first few rows of willows, to retain some windbreak effect but at a distance and we only have two false acacias, so we’ll keep an eye on the relative humidity of the closest bed relative to others to see if the roots are unfavourably drying out the bed.  For me, permaculture is a “work in progress” and all the more useful thought of like that.