Autumn's gilding has gone undisturbed this year. Great drifts of colour lie where they fell, the glorious blessing of sloth. Covid-19 silenced the busybody cacophony of leaf blowers at just the right moment to leave gutters everywhere full of red and gold.
There will be fretting, no doubt. Lawn keepers will be beside themselves. Council stormwater managers will have been praying away the rain.
But the growing piles of leaves have provided a reminder of what a huge resource is available to gardeners at this time of year.
"It is quite lovely just to watch nature do its thing," organic gardening and permaculture educator Michelle Cox says.
What nature’s deciduous trees have done, is to withdraw the chlorophyll from their leaves to store in their roots over winter and jettison the carotenoid-rich remains.
Besides their colour, the leaves also contain a wealth of carbon, a critical component for gardens and one that can be recycled.
"Leaves are carbon. They are high in carbon, high in lignin," Cox, of Waikouaiti-based Organics Unearthed, says. "They are the types of components that fungi in particular need to feed on and as habitat."
And fungi, she says, are the most important life form in soil for plant health, as currently understood.
Carbon is often the element that’s in short supply in a household environment. There will typically be plenty of green nitrogenous material to compost, peelings from the kitchen and garden waste — lawn clippings, prunings and the battered outside leaves of cabbages.
Soil carbon is like a magnet, Cox says.
"It holds on to your nutrients, but it also absorbs moisture, so it’s like a sponge. And at the same time, amazingly, it assists with drainage, so there’s balance there, and it also provides habitat."
Now is the moment to fill the proverbial gardening boots, Cox says.
"Grab the car, grab some sacks, take the kids, rake it up — it’s nice and light, it’s not going to be hard — they can all join in."
Leaves can be gathered either to use in a compost heap, piled on their own to break down or used as a mulch.
Some leaves take longer than others to break down. Oak leaves have higher tanins, so will linger longer.
Willow, poplar and silver birch will all decompose more quickly.
Mulching is another use for those leaves, but gatherers would do well to be a little fussy here. Leaves with black spot or silver leaf should be avoided, as there’s a risk infection could be spread. Walnut leaves might also not be best, as they contain the compound juglone, which is designed to put off competitors.
We should never leave soil bare, Cox says. It’s unnatural.
"Soil will heat. On a hot summer’s day you might get 10-15 degrees in the soil under a mulch. It can hit 70 degrees in summer when it has full sun on it."
Nothing can live in that.
Mulching could pay particular dividends this year as temperatures have been usually high, so soils have remained warm, Cox says.
"If you get that leaf mulch on to the soil now it will hold the soil warmer. It is like putting a blanket on for winter."
That warmth will help with plant growth by keeping roots warmer.
Mulch will also suppress weeds, so there’s more time to sit back and enjoy the garden.
"Come spring you are going to have a lovely lot of organic matter down into the soil.
"You are feeding your soil life. It’s like our digestive system. We know how important it is for our immunity to keep a happy digestive system. It’s the same with the soil. When you keep a healthy soil life you create an environment where plants thrive. The health of the soil provides that immunity, that strength for the plants."
It’s also a form of carbon sequestering, taking carbon permanently down into the soil. "So we are drawing down carbon dioxide in a very gentle way."
Tips for composting
"That’s your moist fresh stuff like food waste, crop waste out of your garden," says Michelle Cox.
The green waste is fast to break down but prone to putrifying in the absence of sufficient carbon.
"So I recommend to people starting out to look at about a 60% volume of carbon to 40% volume of nitrogen. You would layer them like a lasagne."
The carbon needs to be moist, so it doesn’t mummify and just sit there.
Freshly gathered autumn leaves should be moist enough, but if they’ve been sitting for a little while and gone dry, they’ll need to be sprayed with a hose before being layered into the compost.
Think about where you are putting your heap.
"A compost heap is a living organism and like us it needs moisture and to be kept out of cold blasts in winter," Cox says.
Don’t choose a dark frost-prone corner. No, give it a good prime sunny spot.
"You really need to think of a cosy spot where you’d like to sit down with a cuppa yourself."
If the heap gets too cold it will slow down and the microbes will go to sleep.
A hot heap can generate 65degC as microbe numbers grow and get to work.
"I have actually built them before inside a tunnel house to keep it warm through winter," Cox says. "You can set up a little seed tray on top to use that heat."
A simple cage of chicken wire will allow the leaves to break down slowly. At the bottom there will be lovely light seed mix for spring. PHOTO: TOM MCKINLAY
Making seed mix
The simplest thing to do with your pile of raked autumn leaves is to make seed mix for spring, Michelle Cox says.
This can involve making a simple cylindrical cage from chicken wire.
"Stick it vertically on the ground, as it needs to be in touch with the soil, so that organisms come up and break [the leaves] down."
Some people put the leaves in plastic bags instead, which can speed the process, but a wire cage will get the job done, she says.
The piled leaves will rot down through winter to provide beautiful light mix ready in spring for seed sowing.
"At the bottom you’ll have this wonderful light mix, which is what the seedlings need so they can push up easily. And it’s nice and dark, so it attracts the heat."
- Michelle Cox, of Organics Unearthed, is an organic gardening and permaculture teacher and workshop facilitator, including of the Dunedin City Council’s composting workshops. www.organicsunearthed.co.nz
