How to Make Leafmould: Free Soil Improver From Autumn Leaves

Leafmould is what fallen autumn leaves become if you gather them up, pack them into a bag or a wire frame while they are damp, and leave them for a year or two¹. Garden Organic calls it "a fantastic natural soil conditioner"¹. It costs nothing but the effort of collecting, and it turns a garden nuisance into something you would otherwise buy in bags.

The method is simple. Collect fallen leaves in autumn, pack them damp into a reusable bin bag or a wire frame, and leave them for a year or two¹. At one or two years old the leaves begin to break up and crumble easily in the hand; that is young leafmould, ready to use as a mulch or soil improver¹. Leave it at least two years and it becomes a dark brown crumbly material with no real trace of the original leaves, which can be sieved and used for sowing seed or potting on¹.

What follows covers when in the year to do it, how to collect and store the leaves, what each grade of leafmould is good for, and the safety points that matter while you are clearing leaves from paths, gutters and around the house.

When to collect leaves, and which ones to use

Autumn is the season for it. The RHS lists collecting leaves to make leaf compost among the November garden jobs, alongside digging the soil if weather conditions allow and cutting autumn raspberry canes to ground level². You do not need to wait for a particular week: collect as they fall, and again after windy weather has brought down another batch.

You can use all fallen leaves in the autumn, even the ones with black spots¹. There is no need to sort through them leaf by leaf, and no need to discard the discoloured ones. If you want to speed up the process, running the mower over the lawn with the blades set high will shred the leaves and collect them in a mix of grass trimmings¹. Mixing grass cuttings with the leaves also increases the nitrate content of the finished leafmould¹.

Pine needles are the one group worth keeping separate. They produce acidic leafmould, which is ideal for mulching ericaceous plants such as rhododendrons, azaleas, camellias, Pieris and blueberries¹. If you garden on acid soil, or grow any of those in pots, a separate bag of pine needle leafmould is worth the small extra effort.

What to do, step by step

The method has few steps, and none of them needs special equipment. What matters is that the leaves go in damp, the container stays put, and you give it time.

1. Collect the fallen leaves. Gather them from the lawn, borders and paths in autumn¹.
2. Pack them in while damp. A reusable bin bag or a wire frame both work¹. If you would rather not use plastic, make a simple heap contained by stems of clematis or recently pulled up runner bean stalks, or a frame of chicken wire held up by posts¹.
3. Water if the leaves are dry. The RHS advises stuffing leaves into black plastic bags, watering them if dry, and leaving them in a cool, shady spot for a year or so before using them as a mulch⁴.
4. Leave them for a year or two. This is the whole of the waiting period¹.
5. Check the grade before you use it. At one or two years the leaves begin to break up and crumble easily in the hand¹. At two years or more the material is dark brown and crumbly, with no real trace of the original leaves¹.

What each grade of leafmould is good for

Young leafmould and well-rotted leafmould are the same material at different stages, and they suit different jobs. Knowing which you have saves you wasting the finest grade on a job the rougher one would do.

Young leafmould, at one or two years old, is the general purpose grade. Use it to cover bare soil in winter, where it protects against winter rains that can wash out soil nutrients; to mulch around herbaceous shrubs, trees and vegetables in summer; to dig in as a soil improver for sowing and planting; and to top dress lawns in autumn¹.

Well-rotted leafmould, at least two years old, is the fine grade. Sieved, it makes a seed sowing mix either on its own or mixed with equal parts sharp sand, giving a low nutrient, fine-structured medium for seed germination¹. It can also be mixed with equal parts sharp sand, loam (soil) and garden compost to give potted plants a healthy start¹.

If you are raising your own plants from seed, the fine grade is worth the wait. Our guide to sowing seeds indoors and outdoors covers timing, depth and germination, and a fine, low nutrient medium is part of getting that right. For more on making compost alongside your leafmould, see composting at home.

Leafmould also works as a mulch in its own right. The RHS describes mulch as a layer of material at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb)⁵. The same guidance appears in the RHS autumn term guide² and its guide to mulching⁶. A mulch around the base of plants reduces evaporation as well as suppressing weeds⁷. If you use a mulching mat or membrane instead, lay it around the base of the plant and peg it down with wire or pegs⁶.

Where leafmould fits in a household that looks after itself

Making leafmould is one of the least costly things a household can do for its soil, and it fits naturally with growing some of your own food. The RHS lists collecting leaves for leaf compost among its November jobs, in the same season as digging over beds and cutting back autumn raspberries². In spring, its guidance is to prepare soil and add compost if conditions allow, meaning the soil is not too wet or frozen⁵. Leafmould spread in late autumn or winter is doing that soil preparation work in advance.

It also has a place in water saving. A mulch around plants reduces evaporation, which matters in a dry summer⁷. Gardeners' advice on saving water makes the same point from the lawn side: set the mower to cut higher and leave the clippings where they fall to act as mulch, and the lawn will bounce back⁸. Leafmould used as a mulch does the same job for borders.

If you are building up a garden that can feed the household through more of the year, leafmould is part of the groundwork rather than a crop in itself. Our section on self-reliance at home sets out the wider picture, from growing your own vegetables to growing fruit at home. Leafmould improves the soil those crops grow in, and it costs nothing but the collecting.

There is a wider benefit too. Planting temporarily stores rainwater in leafy canopies, which is one reason trees and planting help with flood reduction⁹. A garden with trees in it is already doing that work; making leafmould from their fallen leaves closes the loop.

Staying safe while you clear leaves

Clearing leaves is ordinary garden work, but a few safety points are worth knowing, and they come from fire and health services rather than from gardening lore.

Dry leaves and debris are also a fire risk around the home. Fire service advice for households is that clearing excess dry leaves and debris from gardens, roofs and gutters, and storing flammable materials safely, can make a difference¹⁰. Rural fire prevention advice is to keep grass and weeds short, remove dead vegetation, and regularly trim trees and bushes near buildings and fences¹¹. If you have a wood burning stove, Fire and Rescue Service guidance is to use well-seasoned, air-dried wood, preferably a minimum of 6-12 months old, and to use a wood moisture meter to test your wood before burning¹². The recommended moisture level for firewood is 20% or lower¹³. Chimneys should be swept quarterly when in use for wood¹².

Damp and mould in the home is a separate matter from leafmould, but the two can meet if you store wet material indoors. Independent guidance is to keep doors closed and windows open in rooms where you shower, cook or dry laundry, use extractor fans, keep furniture away from walls, and clean mould off walls to stop spores spreading¹⁵. Damp and mould can make existing conditions like asthma or arthritis worse¹⁵, and if you think you have damp or mould in your home, it is important to deal with it quickly¹⁶.