Tuesday, 22 October 2013

Horse Chestnut Leaves for Leaf Mould

Aha, it's that time of year again - the questions about leaf mould are starting to appear!

Leaf Mould is a subject dear to my heart, nearly as much so as proper compost,  and I'm always writing (and talking) about it, so here is a brief overview:

Compost = garden waste, aerobic  process (needs air) done by bacteria (and worms), takes 6 months to a year.

Leaf mould = leaves only, anaerobic process (does not require air, ie no turning) done by fungus, takes two years.

The result is also different:

Compost = nutritious, full of goodness.
Leaf Mould = not a lot of nutrition, but lots of minerals: mostly to be used as a soil conditioner or mulch.

"Not much nutrition?" I hear you say, "So why make it?"

Well, if you have a lot of leaves and put them on your compost heap, you will ruin the compost. Leaves take a lot longer to decay than green waste, and it's a different process, so if you pile them into your compost bins they will still be there in a year's time, and will have interrupted the worms in their digestion of the green waste.

(I say "green waste" , by the way, when I mean the mixture of green and brown stuff that goes in the compost - soft herbaceous material, annual weeds, and a smaller amount of small woody twigs and so on.)

But leaves arrive in copious quantities, and they are free, so if you have the room to make some pens for them, and the patience to wait two years for the result, then why not?

How To Do It:

1) Make some pens - they don't have to be particularly sturdy, unlike compost bins, you can use just chickenwire and a post in each corner.

2) Fill with leaves, preferably wet ones.

3) Leave for two years.

Yes, it really is that simple.

If you really want more detail:

1) Make the pens about a yard square or more if you can. Make several - they will need to sit there for two years, and the leaves will come down every year, so you need at least two sets of them. Just as with compost, three sets is best: you can manage with fewer pens if you are prepared to put in some work, but if you want the best result for the least effort, make three sets. If you don't have enough leaves to justify making permanent pens, you can make quite decent leaf mould with black plastic rubbish sacks: stuff them to the top with wet leaves, tie the tops, and leave them in a stack somewhere out of the way.

2) Which leaves, why wet, can you shred them, and can you mix them? Wet because the process is fungal, so they need to be dark and damp in order for the fungi to flourish. Shredding is not necessary, so why waste effort/fuel? In my experience, the shredded pieces do not rot noticeably faster than the full sized leaves. Yes, you can mix all sorts of fallen leaves, as long as you avoid the following:

Horse Chestnut - they take a long time to rot, and the rachis (central ribs) never do.
Evergreens - holly, laurel, conifers.
Road sweepings - they will be contaminated with dirt/pollution/spilt fuel etc.

3) Leave them undisturbed. Really! That's all you have to do. Fungi like it dark, and wet, and they don't like disturbance. The leaves shrink massively once they start to rot, but don't be tempted to put the new season's leaves on top of the old season's ones, otherwise you can't get to the good stuff to use it - start a new pen for the new autumn.  There is always a temptation to combine two old pens, when they have shrunk down to just a couple of inches, but it really is better to just leave them.

"Why three sets?"  Ah, to avoid work, that's why. You can manage with two sets - I say "sets" because one pen is never enough - if you don't mind having to turn out the "first" set into bags so that you can re-use them for that year's leaves. But if you want to do the minimum of work, then have three sets.

The resultant "stuff" is lovely, dark, crumbly, non-smelly and wonderful for improving the texture of your soil. It loosens up clay, helps all soils to retain water, gives body to poor, sandy or dusty soils, and it can also be used for potting up and for seeds, if you mix it 50/50 with whatever you normally use.

As mentioned, it does not contain much in the way of nutrients, but is very beneficial in these other ways: and has the massive advantage of not containing weed seeds! This makes it additionally useful as a mulch - you can spread it around on the surface of the beds, where it will suppress annual weeds and help the soil below to retain moisture.

Most of my clients now have leaf mould pens, and whenever I am planting out, or digging over a bed, I add a barrow-load of mixed home-made compost and leaf mould. Lovely! 


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