Mythbust: Fallen leaves are full of nutrients
I'm running behind with raking up my leaves this year due to the recent very wet weather. So in the meantime I thought I'd write a bit about making and using leaf mould.
Every autumn most of the gardening magazines recommend making leaf mould, and quite a few of them claim that this is a good idea because it's full of nutrients. So here's a table showing the average percentage of nutrients plants need in the soil, alongside the average amounts found in leaf mould and in more general home made compost:
(Numbers refer to the sources for my figures, links provided at the end of this blog article)
As you can see, leaf mould contains a lot of Carbon (organic material) but is generally very low in nutrients. More general home compost is more nutritious, although even that is not sufficient to make a good compost, it's better mixed with commercial compost or garden soil.
So, what should you do with your leaves? If you have a suitable spot where they won't be a nuisance, eg under a large shrub or tree, it's useful to leave some leaf piles in place for wildlife: grubs hide in them for birds to feed on; hedgehogs and pollinators may overwinter in leaf piles; butterflies lay eggs on them; earthworms love them.
And even though they're not much use as fertilizers, both leaf mould and home-made compost make great mulch. Not only can suppress leaves, they also act as excellent soil conditioners. They bind sandy soils to help them retain water but break up clay soils to improve drainage. Adding a little to potting compost can make it go further and save you money (I suggest adding about 1/5 leaf mould or home compost to 4/5 potting compost).
If you want to make leaf mould you can put them in leaf bags (either specially made ones or bin bags with holes punched in them for drainage and airflow - see my technique in the photos below) or mesh bins . I leave mine behind my shed for a couple of years, occasionally watering them if they become too dry. When they're well-rotted I spread a 3-4" layer over my borders.
(Left to right: commercial leaf mould bag; puching holes in a rolled up bin bag; unfolded bin bag; filled bin bag)
You can of course just add the leaves to your compost heap, but they will slow down the decomposition of the whole heap and reduce its nutritional value. Mowing over your leaves or putting them through a shredder can help them to decompose more quickly but may harm any bugs hiding in them. I’d advise keeping them separate as outlined above.