Leaf mould is one of the best mulches or soil conditioners around and the good news is that anyone can make it. All you need are autumn leaves, and time. Rakes or boards, or a rotary mower, to gather leaves will make life easier, and a fenced containment area will keep your heap in place in high winds. Make leaf mould this autumn and in a year's time it will be great as a mulch, in a couple of years it will be broken down into a lovely, crumbly soil conditioner that will be perfect for replenishing fertility in your polytunnel.
It is possible to use black bin bags with holes pricked in them to store your leaves. However, should you prefer to be more sustainable and avoid using the plastic then you can easily just make a mesh bin or fenced off area in which to store your leaves as they rot. Allow for plenty of ventilation in the structure so the leaves do not get slimy and air is able to circulate. It is also best to create some sort of lift-able cover for your leaf pile so it does not become too wet. (Also, in very dry weather, it is best to sprinkle your leaves with a little water to make sure that the decomposition can continue.)
Do not worry about getting some grass in with your leaves, this will just make your leaf mould richer in nutrients. Do try to avoid spreading weeds into your leaf mould pile as these could become a problem if you do not keep on top of it. Other than collecting the leaves in the first place, and keeping a bit of an eye on things, it is just a question of waiting for nature to do its thing.
Fallen leaves in the autumn are a useful commodity. Even if you do not have many fallen leaves in your own garden, you may be able to collect some from the gardens of family, friends or neighbours, or even from a public space/ open land. Remember, however, that not all leaves were created equal when it comes to making leafmould.
Oak, beech and hormbeam leaves are best of all. Though all deciduous trees' leaves will work fine, some thick leaves such as sycamore and horse chestnut will take far longer to break down – shredding them can speed up this process. It is best not to add evergreen leaves to your general purpose leaf mould pile and pine needles are best kept separate to make a separate leaf mould that will be perfect for acid-loving plants.