Autumn leaves aren’t just pretty, they’re full of essential minerals for your garden.
The problem is they fall in such numbers that they can overwhelm the compost bin or form an impenetrable layer if left on the ground.
They are best composted separately in a leaf mould heap, where they break down via a special type of slow, cool decomposition driven mostly by fungi, rather than the warm, fast action of bacteria in a standard heap.
Leaf mould produces a wonderful end product that can be dug in to improve any soil, used as mulch or incorporated into potting mix.
And forget the balancing and turning of traditional compost, just pile up the leaves, wet and forget.
For the best leaf mould, use leaves from deciduous trees, leaving out any with fungal or viral infections.
If you don’t have enough in your own garden, collect them from footpaths and nature strips in the neighbourhood. Leaves from evergreen trees break down more slowly, so keep them to a minimum.
In six to 12 months you’ll have a rich mulch to use on pots and garden beds and within a year or two, a nutritious soil conditioner that also makes a brilliant addition to homemade potting mixes.
TIP Large leaves left on the lawn block sunlight, which can weaken turf. Run the mower over the lawn with the catcher off and the shredded leaves will soon disappear into the grass.
Make leaf mould
Although you can make leaf mould with just a heaped-up pile of leaves, the process is easier to manage with some sort of container.
In a small garden, use the bin bag method. Collect fallen leaves and save them in a garbage bag, hosing with water to soak the whole lot.
Make a depression in the top of the tied-off bag and punch a few holes to let in rain. Punch more holes at the base to let excess moisture drain out and keep the bag in a shady area.
If you have space, build a leaf bin, which will allow you to pile your leaves as high as possible. They’ll rot down, so don’t worry if your pile is tall to begin with.
Leaf mould can take two years to rot, so have more than one bin if you want to use it fully rotted.
TIP Plane and sycamore leaves can take three years to rot. Shred them finely or run over the pile several times with a lawnmower to speed things up.
Feed the garden
Depending on how long you leave it to break down, leaf mould has many uses in the garden.
It is ideal for use around trees, shrubs, perennials, woodland plants and ferns, while annuals and vegetables prefer the higher nitrogen available in normal compost.
Young leaf mould is usable after six to 12 months when the leaves start breaking up and crumble easily. Use this young product to mulch garden beds and around trees and shrubs, dig it into the soil to add organc matter before planting, or use it as topdressing for lawns.
Well-rotted leaf mould is a dark brown crumbly material that’s produced after one to two years, with no real sign of the original leaves.
This material can be used the same way as young leaf mould but also as seed-raising mix. Or combine it with equal parts washed sand, loam and garden compost to make potting mix.
How to build a leaf compost bin
To make leaf mould, build a bin in a sheltered part of the garden where rain can still get to the leaves, like next to a shed, as they decompose faster if kept damp.
Step 1. Measure out a square or rectangle to fit your space. Position a garden stake at least 1000mm high at each corner and hammer firmly into the ground.
Step 2. Secure chicken wire to the stakes with galvanised staples to enclose the bin on three sides. The front is left open so you can add the leaves to the bin.
Step 3. Pile up leaves to the top, wetting them down with a hose. When the bin is full, add a mesh front with tie wire so you can remove it to access the leaf mould.
Which leaves to use
These trees have mineral-rich foliage that breaks down slowly to make a rich soil conditioner. Small leaves rot faster, so shred large or thick leaves.