November 18, 2013

All the Leaves Are Brown

We are coming down to the end of the garden clean-up.  The perennial beds have been cut back to stubs and even the grasses are looking weary.  What we are left with are… oak leaves.
We have perhaps two hundred trees on our two-acre property.  There is a healthy mix of specimen trees we planted over the past 14 years (oxydendron, forest pansy redbud, heptacodium, dogwood, cornelian cherry, etc.), but the preponderance of our little forest are trees that were on the property when we got here. 
This fifty-foot oak on our
property still has some leaves
to shed.
Among the latter group are twenty or more oaks.  The largest are over fifty years old and sixty feet high but we have them in all sizes.  What all of the oaks have in common is that they all wait to drop their leaves until after the other trees on the property have done so. Around our home, the maples, ash and birch all shed their leaves in October.  Even the pines completed their needle drop by the end of the month.  It is now mid-November and a good gust of wind can still bring down a cascade of oak leaves.
The lawn was mowed yesterday.  Last
night's storm left it looking like this.
Oak leaves are the savior of lawn services.  Maples, for example, drop their leaves quickly:  typically in two weeks or less.  Moreover, they are ‘thin’ leaves and their C:N ratio (carbon to nitrogen) is around 20.  This means they break down very rapidly when simply mowed into the lawn.  The mulched leaves return the same nutrients needed for next year’s growth.  Lawn services, or course, are not in the business of letting Mother Nature do for free what three guys with a truck can do for a fee.   When the maple leaves fall, there’s a single visit to rake/suck up the leaves and leave the lawn looking neat and tidy.  Lawn ‘nutrition’ will be added later in the form of a ‘fall (chemical) fertilization’.
If not cleared, oak leaves will form
a mat that smothers whatever is
underneath it, like our rock garden.
Oak leaves, on the other hand, can take a month or more to drop.  Their C:N ratio is 60:1 and the leaves are both thick and heavy with tannin.  What this means is that the leaves decompose very slowly (because of the preservative property of the tannin) and, once on the ground, they stay there.  A diligent lawn care company can milk oak leaf season for half a dozen clean-up trips.  Clients pay because there are few things as ugly as an oak-leaf-strewn lawn.
We, of course, don’t use a lawn service.  The earlier, non-oak leaf drops were all mowed into the lawn and have long since disappeared.  The oak leaves, on the other hand, have another fate: we turn them into mulch.  It’s a laborious process but well worth it.
Here’s what we do:  first, we rake all of the leaves out of the various beds and onto the lawn.  We do this because oak leaves tend to mat.  Because they’re not drying out after they fall, they’re still pancake-flat after several weeks.  If you get a layer of oak leaves six or eight thick, it turns into a smothering blanket over your lawn or perennial bed and little moisture gets through.  The result is snow mold and other diseases.
These chopped-up oak leaves are
spread on our beds as a protective
mulch for the perennials.
Next, we chop up the leaves with our lawn mower and bag them.  Then, the well-chopped leaves go right back onto the beds as a mulch.  They won’t mat because they’ve now been torn into tiny pieces.  Bacteria have a lot more edges to chew on, hastening their composting. The oak-leaf mulch provides insulation for the plants in the beds (preventing heaving), a moisture barrier to keep water in the soil from evaporating, and a slow-acting compost to enrich the soil.

By spring, the oak leaves will have mostly disappeared and we’ll put down a layer of brown wood mulch for the season.  In the meantime, we’ve taken a problem (those drab oak leaves) and turned them into an asset. 

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