Every Autumn/fall we see leaves raining down from the trees. Some people see them as a problem that gathers up and blocks the drains. Others see them as an opportunity and gather as many as they can before they’re blown-off to else where into someone else’s garden. If you want to be the opportunist and make compost from this annual bounty, you may be wondering how long before you’ll see any usable compost.
How long does it take leaves to decompose?
So, how long does it take to compost leaves? It will take at least 12 months if you want a finished, black, crumbly compost that’s ready to use in the garden. Making compost from leaves does require patients and some effort. If you don’t turn the heap over it may take even longer. Adding white-lime and lawn clippings does improve the process. Having a good mixture does mean composting leaves won’t take too long.
There are things you can do to speed it up;
The first thing to do is to gather up all the leaves into a large pile, or into a large container, whether a pallet-framed setup, or some way of holding a heap together.
Any composting container can be used for composting leaves, for example, our Rolypig Composter is well suited to take smaller volumes of leaves. It maintains the best conditions for composting inside. This is speeding up the composting process by keeping things damp inside the barrel.
Composting leaves in plastic bags is a good method, this keeps the moisture level high, but composting needs air, so be sure to shake the bags up, from time to time. Keep the tops left open all the time.
How long does it take leaves to decompose? Give them 12 months.
Let’s not forget the part that worms can play in making compost from anything that’s organic. Most gardens are going to have worms in the soil. Dead leaves are carbon based and were once living. Worms will digest dead leaves, in the right conditions. We have written a post that looks at the effects of worms in compost. See it at Worm composting.
You may be wondering if it’s worth the effort to make compost from leaves. After all, they are spent-out and dead. What value can leaves have? Done properly, compost made from leaves is an ideal source of organic fertilizer. We have a post that explains this. See How to make organic fertilizer from leaves, to find out more
Oak leaf compost.
Oak leaves can be tricky, because of the natural preservatives in these leaves, so, oak leaves need mixing in with a larger pile of other leaves.
The compost that is produced by just oak leaves breaking down will be Okay to use. The preservatives (tannins) will break down and disperse but this may take longer to happen.
Pine Needles Compost.
Pine needles and waxy leaves are more problematical than broadleaf leaves.
It would help if you could put them through a shredder. This wouldn’t take much effort and it would bruise the the pine needles enough to help them break down.
It is always best to mix these waxy leaves with other types of leaves if possible.
Leaf compost, in general.
Leaf compost is a bit different from compost made from general green waste. This is because leaves are drier at the point of collecting them. So dry, that a good watering is needed to allow the bacterial and fungal organisms to get to work on them.
It can be a good idea to store up dry autumn leaves to add to the wetter green waste taken from the kitchen, so that the mix aids with composting right through the year.
Store the leaves in a dry condition, because, if stored loose and just damp, there are many rotting fungi that will just rot the leaves. Just rotting, going mouldy, is not going to produce a usable compost material. Far better to mix in with the green wastes mentioned above.
The waxy leaves, from evergreen shrubs and cypressus-type trees, are a different story. These leaves just do not break down very quickly at all, unless you macerate them (chop them to the point of a mush!).
It is better to just heap these types of leaves up, and cover the pile with soil. Leave the pile to rot over a number of seasons. Leaves will take the time that it takes to turn into compost. It will rot eventually, and while it does so, you may like to know that it will be a home for many invertebrates.
The term ‘leaf mould’ is often used in connection with dead leaves on the forest floor. Usually undisturbed from the time they have fallen from the trees, these leaves start to make up a humus-rich layer. Sometimes this layer builds up, and, exhibits a profile of rotted dark material underneath, with still-recognisable leaves sitting on top.
Leaf mould is not a product of a composting process, as we would, normally, recognise it.
This means that we would not aim to produce leaf mould by the natural process on the forest floor.
It is far more efficient to stack up the dead leaves in autumn to compost them, or, store the leaves dry, for use all year round to add to the wet vegetable waste in the compost bin or pile.
Consider leaf mulch.
It could well be a better option for some leaves from ornamentals, to use them as an open mulch around shrubs and other perennials in the border.
This is a good way of suppressing weed growth, retaining soil moisture, and, returning nutrients to the soil, all in one go!
The only thing to worry about, is, a possible safe harbour for slugs, who will live in leaf litter in some situations.
My experience is that songbirds love turning over leaf litter..and discovering the helpless molluscs hiding within!
Using leaves as a mulch is, pretty much, mimicking nature on the forest floor, and usually gives great results.
Dead leaves could be the best mulch for raised bed vegetable garden, as long as the leaves are not from a known diseased shrub or tree.
If the leaves have senesced early, that is, died off during summer, and dropped from a very sickly tree, then it is best to burn these leaves as soon as possible.
A healthy leaf mulch is a very useful way to suppress weed growth around vegetables, with the added bonus of retaining moisture in the soil.
Some care has to be exercised on heavy (clay) soils, to prevent excessive dampness around the base of crop plants by having too thick a layer of mulch.
Too much fresh mulch can increase the risk of fungal diseases attacking the crop plants, and also it can prevent air from getting into the soil.
As always, there are mechanical devices to make leaf muching easier and quicker.
To sum up.
How long does it take to compost leaves?
Be ready to wait at least 12 months if you want a finished, black, crumbly compost.
Add enough water to keep the leaves moist.
You can speed the process by turning the heap over.
Add hydrated white-lime to neutralize acids.
Add fresh-cut lawn clippings, the nitrogen will balance the carbon in the leaves.
Store dry leaves and gradually add them to a compost bin throughout the year.
How about gum tree leaves?
Can you put gum leaves in compost?
You can put gum leaves in compost but the general advice is to limit the amount that you add. Gum leaves from the Eucalyptus tree carry a toxin-issue which may compromise a compost pile if you add too many gum leaves. To avoid problems it may be wise to make a separate pile of just gum leaves to protect the main compost pile.
The eucalyptus tree needs to be understood. They want the world to themselves and they know how to clear a space to be able to get it. They are very aggressive in the way that they can generate naturally occurring, toxic chemicals. This makes the ground around them almost completely uninhabitable to anything, other than themselves.
This is where the leaves and other bits of flotsam, that fall from gum trees, render the ground almost useless to any other plant. Gum trees produce a toxin that comes through to the leaves.
The gum tree isn’t the only plant in the world that does this. There are other plants that are very successful at doing this. An example is the common dock. If you look under or immediately around a growing dock plant, you will see bear soil. The standing dock plant emits enough toxins to prevent any growing-competition around them.
The gum tree weaponizes its leaves in the same way as the dock plant suppresses other plants. So, this poses the question of what effect these toxins would have if they get into the compost from gum leaves.
There’s been research done by the Universities of California, Arizona and others who’ve established that leaves and other fallen material from the gum tree will make compost that’s safe to use.
However, it must be stressed that compost made from such material needs to be fully formed as only completely composted material will have no traces left of any of the original toxins.
The research also found that a composting mass that generated heat, would be the most effective way of rendering out the toxins.
There is another side to this issue. Fresh gum tree leaves can be used as a mulch with the intention of working as a way of keeping down weeds.
There’s also a suggestion that gum tree leaves or gum tree material, could be used in a mushroom-growing medium as a way of suppressing any other forms of germination.
Should I till leaves into my garden?
You shouldn’t till leaves into your garden soil. Leaves need to be spread, thinly, over a wide area and allowed to rot on the garden-soil surface. The worms will till the soil enough when they pull the decaying leaves into the soil. By avoiding tilling you will retain more, of any, nitrates in the soil.
The latest buzz-phrase is ‘no till’. This is good news because it means that we no longer need to spend hours doing the back-breaking work of digging soil.
To understand how ‘no-till’ works, we need to think about what happens in the natural world where nature takes care of everything. If we think about a forest-floor, there’s no one there to till the soil where leaves fall.
The leaves that fall will build up into a substantial layer and just stay where they are. Unlike in a garden where there is someone around to keep things tidy, leaves on the forest-floor will rot down where they sit.
This process will go on year after year. There will be a build-up of high-quality organic material that will be high in carbon. Almost anything will grow in this layer on the surface and it will have been achieved without any tilling taking place.
Where possible, you need to try to achieve the same result as the forest-floor, in your garden. When you have access to any quantities of leaves, you can manage their use in the garden without doing any tilling.
To get the best results from leaves, you need to spread them over the ground where you intend to grow your preferred plants. This needs to be done in the autumn/fall time when the garden is going into the winter dormant period.
So, just spread out your leaves and walk away and leave it. Don’t go poking at them or doing anything that approaches tilling.
There is an advantage in doing this. During the winter months, your garden will probably be subjected to several inches of rainfall. Soil that’s been tilled in any way will be open to the sky. Every drop of rain-water will hit this tilled soil. The result of this is that some of the soil will become mobile.
Constant rain on tilled soil will eventually become washed away. This would be a disaster for any garden. If you have a layer of leaves on top of any tilled or loose soil, the leaves will act as a roof, stopping the rain.
This natural roof will rot down eventually but it will still have a partial effect of protecting the soil. The rotting leaf material will be taken into the soil surface by worms. If anything should be allowed to do any tilling of soil, it should be left to the worms. They won’t inflict the level of disturbance to garden soil as you would do when tilling with garden tools.
There is a down-side to allowing leaves to build-up on the soil surface that many, quite rightly, point out. When leaves break down, when in direct contact with soil, tilled or otherwise, any available nitrates in the soil, will be released and lost.
This is considered to be a small price to pay. Maintaining sufficient nitrate levels in garden-soil is almost impossible. Most gardeners resort to adding bagged artificial nitrogen fertilizer to make up the shortfall.
If you’re not keen on the idea of artificial fertilizer there is another option that will bring nitrates into the garden. Grow a cover crop of a legume variety. Legumes will take nitrogen from the atmosphere and fix it in the soil. The type of plants you can try for this would be clover, peas or vetches.
This may involve allowing a full growing season for a patch of ground in a garden to build up nitrates. It may be possible to establish the crop over the winter months but this will depend on the winter weather.
The cover crop plants can be cut away and collected. This can be used for making compost as you would with grass clippings. The compost from the cover crop can be added to the soil knowing that no more nitrates will be lost from the rotting of the crop itself.
Where there is a layer of rotten leaves that have been there over the winter, seeds can be sown into this. You now have to consider the tilling process. The minimum of tilling is what you’re aiming for. It’s possible to till the surface that includes the recently rotten organic material of the leaves.
The leaves, by this stage are now compost. Some of it will have been taken down by worms. It shouldn’t be necessary to till the soil beneath the compost line but slight tilling will help the seeds to become rooted.
Treating your garden like the forest-floor will allow for the gradual build up of organic material on the surface of the soil. This is exactly where you want both the structure and nutrients that any organic material provides.
Image sources: Gum tree leaves