Leaves are a rich harvest for your garden’s soil. Raking up and hoarding fallen leaves is one of the best things you can be doing for your garden in autumn. By early winter you should have every leaf that has fallen from every deciduous tree within your reach stashed away and ready to rot.
Fallen leaves are pure gold for the gardener. As they break down, soils wake up. Worms and mycorrhizal fungi love them, plant roots too. Autumn leaves decompose into humus, a fine, dark crumble that opens up soils and helps them retain moisture and nutrients.
The process doesn’t even require finessing. Leave leaves wherever they fall and break down they will. Go one step further and pick them up and scatter them over garden beds and you have free mulch that worms and fungi can gradually work into the soil.
Another option – especially good for big leaf hauls – is to make leaf mould by letting piles of fallen leaves break down for a year or two. Gather all your leaves in either wire cages, tough bags with holes punched through, compost bins or compost bays. Keep the leaves moist but not straight-out wet and don’t pack them so tightly that air can’t circulate through.
Then – aside from watering the pile in dry weather – leave them to their own devices. It can take up to two years for them to be reduced (you will be shocked by how much) into a high-carbon soil improver. Unlike almost every other aspect of gardening, making leaf mould is largely set and forget. But it doesn’t have to be. You can be as interventionist as you like. Shred your leaves with the lawn mower before piling them up and they will break down faster. Add a sprinkling of blood and bone or manure and the resulting nitrogen hit will help bacteria get to work and speed up the process even more.
Be aware though that the more ingredients you add the more your blend is edging closer to being compost than leaf mould. The difference is that leaf mould is lower nutrient being a reduction of just one ingredient – carbon-rich leaves – while compost is nutritionally richer and contains a host of other items that are strong on carbon (stems, roots, twigs, straw, paper) as well as some that provide nitrogen (kitchen waste, coffee grounds and lawn clippings).
While leaf mould and compost can both be added to soils to increase vitality and improve structure, mix them together and add sand and you have a seedraising mix. Add a slow-release fertiliser as well and you have potting mix. And at this time of year great lashings of leaf mould can be made with minimum fuss. Not all leaves rot at the same rate, however. Some (oak, elm and linden, for example) break down faster than the likes of plane, magnolia and walnut. It is also possible to add some of the leaves that fall from evergreen plants, though again these can take longer to break down.
As for where you gather your leaves, well there are really no limits. Your own garden is an obvious place to start but avid leafmould makers will invariably find themselves looking hungrily at the thick carpets of leaves that fall in parks and streets. Check with local authorities before helping yourself.
The best time to gather fallen leaves from public places is immediately after rain when they are handily washed into easy-togather piles on low-lying gutters. The key thing to bear in mind is that a garden is only as healthy as its soil, and that there’s no time like the present to get working on it.