As the days shorten and deciduous trees drop their leaves, many of us reach for the rake and start bagging them up for the green bin or a trip to the transfer station. But fallen leaves are one of the most underrated free resources in the garden. Left to break down, they become leaf mould and mulch — a beautiful, crumbly material that improves soil structure, holds moisture, and feeds worms and microbes. Sending them away means paying to dispose of something you'd otherwise happily buy in a bag from the garden centre.

The simplest approach is to use leaves as a mulch straight away. Rake them off your lawn and paths (leaves left on grass over winter can smother and kill it) and spread a layer several centimetres thick around the base of trees, shrubs, and garden beds. This blanket suppresses weeds, protects soil from heavy winter rain, and slowly rots down to add organic matter. Keep the mulch a few centimetres clear of plant stems and trunks so you don't trap moisture against them. Shredding the leaves first — by running the lawnmower over them — speeds up decomposition and stops them matting into a soggy layer.

If you want to make leaf mould, the fungal-rich crumbly compost that leaves produce over time, just gather them into a simple wire cage, a corner of the garden, or a couple of black rubbish bags with a few holes punched in and a splash of water added. Unlike a hot compost heap, leaf mould is made slowly by fungi rather than bacteria, so it doesn't need turning or a careful balance of greens and browns. Give it patience: a rough mulch is ready in six to twelve months, while a fine, dark leaf mould can take a year or two. It's worth the wait — the result is a superb soil conditioner and seed-raising mix ingredient.

A few leaves are best kept out of the pile. Avoid using leaves from plants known to be toxic or very slow to break down in large quantities, and be cautious with diseased foliage — leaves showing signs of fungal problems like black spot are better sent to your council green-waste collection where hot commercial composting can kill the pathogens, rather than returned to your beds. Walnut leaves in particular contain compounds that can suppress other plants, so compost these separately and use the result sparingly. Otherwise, most common New Zealand garden leaves — oak, maple, liquidambar, elm and the like — are perfectly good.

Leaves also make an excellent 'brown' ingredient for your regular compost bin or worm farm. If your compost tends to get slimy and smelly from too many kitchen scraps, stashing a bag of dry autumn leaves nearby lets you add a handful whenever you need to balance out the wet greens. This keeps the heap airy and odour-free right through the year, long after the trees are bare.

So before you bundle those leaves off to the kerb, remember they're free fertility for your patch. Whether you spread them as mulch, cage them into leaf mould, or store them as compost fuel, you'll be building healthier soil, saving on bought mulch and green-waste fees, and keeping organic matter out of landfill. If you do have a genuine surplus, your council's green-waste or food-scraps collection is the next best home — check your local council for what's accepted in your area.