4

The city where I live is running a campaign to keep leaves out of the streets, where they contribute to phosphorous in storm water run-off causing lake pollution.

I'd like to avoid the need to send/take my leaves anywhere, which invariably would require some or all of:

  • bags (possibly plastic)
  • fossil-fuel burning vehicles
  • dead patches of grass where leaves are piled while waiting for transport
  • extra work

I already have a compost bin in my yard where I dispose of food scraps and the occasional scoop of grass clippings.

Will adding a large volume of fallen leaves to my food waste compost bin cause any problems? Should I have a second bin only for leaves?

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In a temperate climate where deciduous trees drop their leaves for the winter such leaves are nearly the perfect compostable material. Trees drop them to mulch the ground for one season and then decompose to return useful nutrients to the soil where those same trees can use them again.

A reasonable generalization for the carbon to nitrogen ratio of recently fallen tree leaves is 30 to 1. The ideal carbon to nitrogen ratio for a home compost pile is 30 to 1.

The nitrogen level in tree leaves does begin to drop soon after they fall so the more quickly you can get the leaves into the compost pile (where the nitrogen can be captured by your composting bacteria) the better.

Thus, recently fallen tree leaves are probably a better composting material than the average household food waste. Adding tree leaves to your household food waste compost pile will buffer the carbon to nitrogen ratio and let you successfully compost material that is further from the ideal ratio.

One issue to watch out for, though, is that mulch goal. A thick, matted layer of leaves will create a layer in your compost pile that is difficult for water and air to penetrate. Starving your pile of air will turn it anaerobic and nasty. The stink of an anaerobic compost pile is the smell of volatile organic compounds escaping - likely including methane. To avoid this, mix leaves thoroughly into the pile or shred them before adding.

If your compost pile ever goes anaerobic (because of tree leaves or any other reason), promptly turn and aerate the whole thing and correct whatever management practice caused the problem.

2

Leaf mould is one of the best composts but leaves should never be removed from under the trees, because the fungi that support the trees feed on them. However leaves in the street are a nuisance and they should be swept up and composted, adding nutrients to the kitchen waste. However waxy broad evergreen leaves can stifle a compost and I think some produce toxins. Not sure how you'd dispose of them. Compost separately with a little slaked lime perhaps.

2

Letting the leaves be taken away from the garden is like throwing out valuable nutrients. As a general practice I put the leaves in the compost bin, and I try to mix them from time to time, or to break them with a shovel once in a while. Two types of leaves I do not put in the compost: evergreens (as mentioned by Janet) and walnut leaves. In our area the general perception is that the walnut leaves contain substances which are causing them to decompose much more slower, but my other reason is that the walnut trees are infected by leaf miner. I let these leaves to be taken away with the trash. It is a bit of an extra work, but if consistently cleaned, the larvae will not hatch from the fallen leaves any more, thus allowing the walnut trees to recover.

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