What is Leaf Mould?
Raking up leaves is part of a gardener’s life.
The best way to make use of all those leaves is to keep them as mulch, compost, or leaf mould: that crumbly, airy, free draining stuff that improves soil, and makes a superb potting medium for seeds and cuttings.
Which Leaves Should I Use for Leaf Mould?
All leaves and conifer needles will make leaf mould … eventually.
The best leaves to use as leaf mould are the fastest to break down: smaller and/or thinner leaves like beech, oak, hornbeam, ash, birch, cherry, elm, lime, poplar, or willow.
The worst leaves to use as leaf mould are slow to break down: thick, big leaves like horse chestnut, sycamore, maple, or magnolia, tough little hawthorn leaves, or any evergreen.
They could be shredded to speed things up, but usually they are better for mixing into a normal compost heap, unless you have nothing else.
Pine needles take years to break down and tend to pass through shredders mostly intact, so aren’t really a practical choice for leafmould.
Making Leaf Mould Instructions
If you don’t have masses of leaves for a big leaf mould pile, the simplest thing is to bag them up in old compost bags, bin bags, etc.
- The leaves should be damp
- Pack the leaves into the bag quite tightly but without ramming them in
- Tie up the mouth of the bag, then stab it a couple of times to allow some air to circulate
- Tuck the bags away somewhere out of sight
- After a year or two, you will have the most brilliant leafmould
Gardeners whose leaf output is too much for a few black bags should build a leafmould pile somewhere out of the way. Ideally, leave room for another to fill one while the first rots down.
- Use four or six tall stakes depending on whether your feng shui demands something rectangular or square.
- Make a wall out of chicken wire tied to the posts: use wire, as it lasts longer than string
- Keep the posts outside the wire. As the weight of leaves increases, it will push the wire onto the support posts, rather than tearing it off them.
- Line the bottom with a bit of Mypex so weeds do not grow up and through your leafmould.
- In a hot dry summer, moisten the pile occasionally to speed decomposition.
Which leaves should I leave out of my leafmould?
While all leaves will make leaf mould (eventually), but to avoid spreading plants diseases, we recommend you always burn, bin, or otherwise dispose of far from vulnerable plants the following:
- Fruit tree / bush leaves
- Rose leaves
This is a precaution against diseases like Apple/Pear Scab and various rusts, leaf spots, and blights.
The rose family includes most of the fruit trees grown in Britain, and they can all share diseases.
Almost all fungal diseases that attack leaves overwinter in leaf litter beneath the infected tree.
With spring and warmer days, rising air currents help the spores back into the tree to re-infect it.
A spore can survive for years until conditions are right, so a leaf-heap is an ideal place to lurk.
Other Benefits of Leaf Mould
Removing leaves from lawns and beds deprives slugs and snails of nice hidey places to pass the winter months. Dealing with the leaves is a way of preventing infestations of these, the bane of all gardeners, and reduces your spend on slug pellets – an all their nasty chemicals – next year.
Leaves left to rot on paths make them slippery and over the years will accelerate your need to repair them.
Leaves left on lawns will ruin the grass beneath them.
Is leaf mould acidic?
No, leaf mould is not really acidic, it has a pH close to neutral around pH 6.5–7.5.
Leaf mould will help lower the high pH of alkaline soils closer to neutral, which is acidifying it.
But if you have neutral or mildly acidic soil and want to acidify it further in order to grow acid loving (ericaceous) plants like Blueberries, then leaf mould will not do that. Adding leaf mould is still good for plants like blueberries that love moist soil due to its moisture retentive properties.
There is a pervasive myth, repeated even by the RHS, that pine needles and leaves from ericaceous plants make acidic leaf mould, which should be reserved for ericaceous plants.
This is potentially misleading: pH 6.1 – 7.0 is “Moderately Acid Soil” according to the RHS, which is ideal for most plants, and that’s as acidic as leaf mould gets.
“Acid soil” is pH 5.1 – 6.0, ideal for most ericaceous plants, and no leaf mould will get that acidic.