Your leaves are an invaluable resource
6 October 2013,
by Kate Harries
Don’t throw those leaves away – they can be turned into leaf mould, a wonderfully fragrant woodsy material that results when you have kept your leaves for two or three years.
Leaf mould contains trace minerals that have been pulled from deep in the ground by long tree roots, it improves the structure and moisture retention of the soil, and it promotes the growth of organisms like micorrhizal fungi that plants need to take up nutrients.
What a waste to put such a valuable resource out on the curb!
Is leaf mould the same as compost? No – leaf mould is the result of a fungal process, while compost is the result of organic matter being broken down by bacteria. Leaf mould is cool and takes time. Compost likes it hot and should be finished as soon as possible. For both leaf mould and compost, it’s important that the pile be in direct contact with the earth, not positioned on concrete or brick.
Gather the leaves from deciduous trees – maple, oak and ash are the predominant species around here, but all leaves are good except for those of black walnut, which contain a chemical that inhibits some plants. Don’t add weeds or lawn clippings – those are for composting (although weeds that have gone to seed are best consigned to the fire pit because your compost might not heat up enough to kill the seeds).
You can build a loose pile, but a more efficient use of space is to make a bin (mine is five feet tall) out of wire or scrap wood. Those with little space can collect their leaves in plastic bags. Moisten, punch some holes in the sides and at the base, and check every few months in case you need to add water.
Ideally, leaf mould should be kept for three years to be fully decomposed. I’m impatient, so I sieve it after two years. This allows me to separate and use the fine, well-rotted material. The larger pieces that haven’t broken down enough are spread as mulch around young or newly planted trees.
I collect my leaves in a large wire enclosure. The 2012 pile has decomposed to about half its original size, and soon I will move the contents into a smaller bin, or series of bins, to allow the process to continue for at least another year, while this year’s leaves go into the vacated enclosure. The 2011 pile - half the size again - is being put to good use right now.
I don’t rake up all the leaves that fall to the ground – nature designed them to provide trees and shrubs with nutrients and act as a buffer against the dangers of drought or frost and freeze-thaw shifts in temperature.
And clearing the leaves away so grass can grow right up to the trunk doesn’t do a tree any favours at all – grass, whether mown or growing long, is a fierce competitor for the water and nutrients the tree needs.
So I leave a circle of leaves out to the drip line to keep the grass down and stop the soil from compacting. Note: as with any mulch, leaves should not be piled up against the trunk, that will cause rot and disease.
Another reason for leaving a protective layer of leaves in some areas is to provide space for beneficial insects and other small creatures to hibernate– and a larder for hungry birds to raid when the frost comes out of the ground. Anyone who has watched returning robins and sparrows diligently combing through the leaf litter in spring will know what I mean.
The decomposition in your leaf mould bin can be speeded up by first running the lawnmower over the leaves to shred them before you pile them up. I see that some authorities – like the Rodale Book of Composting – advise that leaves collected while they are fresh will break down faster as they contain more nitrogen and the cell structure hasn’t dried out and hardened. I can’t say this is something I have ever worried about. Including some finished leaf mould to the new leaves is also said to kickstart the process.
Once the pile is completed, there’s not much to do except wait. Moisture is helpful, so in times of drought, add some water. And turning the pile is a good idea, because the leaves on the outside dry out, and some on the inside form tight layers that resist breakdown.
But really, the most important part of making leaf mould is to let nature do the work and not be in a hurry.
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