A reader said he had heard of the practice of shredding leaves prior to using them as mulch but wondered about the reason behind it. Was it just to make it easier to dispose of the leaves, since, once shredded, the load would be more compact? Or was there some other benefit? The answer follows:
One Reason for Shredding Leaves: More Efficient Disposal
After raking leaves in the fall (the reason for which is explained here), you take the additional step of shredding them with a leaf shredder, lawn mower, or other device.
Most people who go through the trouble of shredding leaves do so for the purpose of using them in the landscape, rather than disposing of them. This is smart, because leaves are biodegradable and a wonderful source of organic matter with which to enrich your garden beds and/or suppress weeds. Why pay for compost and mulch when you can make your own?
But if you do decide to dispose of the leaves that you rake up in fall, shredding them first means there will be fewer air spaces when you stuff them into the disposal bags. Having less air spaces means, in turn, being able to cram more leaves into each bag. The result is that you will use fewer bags.
A Second Reason: Superior Mulch, Quicker Compost
The best mulches are porous enough to permit the penetration of air and water to the soil, thus promoting plant health.
While not a consideration in the winter for vegetable gardens and annual beds (in case you need to mulch these areas in winter just to prevent erosion), this becomes a factor if the mulch is to be used once spring rolls around again. Thus the reason for shredding leaves for use as mulch: An application of unshredded leaves would mat down, forming an imperious layer that would not "breathe" and that water would run off.
This state of affairs would not be good for the plants in the garden beds in question.
If you garden organically, you will probably applaud the fact that leaf mulch will not remain leaf mulch forever. Leaf mulch is just compost waiting to happen. That is right: as the leaf matter decomposes, valuable nutrients will be released into the soil and made available to your plants. While you lose your mulch as a result of this process, you more than make up for the loss by gaining compost. You can hasten this natural process by shredding leaves before applying them as a mulch.
What has just been described is compost production that does not involve a structure set aside to house decomposing matter (termed a "compost bin"). That is, you set out primarily to make mulch, but you end up with compost as a bonus. Of course, some gardeners skip the mulch phase altogether and just place the shredded leaves directly into a compost bin, for the purpose of breaking them down into organic matter as quickly as possible. Here, too, shredded leaves work better. The reason? The typical compost pile works best when aerobic organisms are allowed to flourish. As that word implies, it is essential that the pile breathe.
Unshredded leaves would mat down and discourage the aerobic organisms you need for efficient decomposition.
Tools of the Trade
Some people use a machine called a "leaf shredder" to do their shredding. Some types vacuum up the leaves, shred them, then gather them into a bag. But this convenience will cost you.
Most wood chippers also shred leaves just fine. The wood chipper is typically more of a heavy-duty device, and you will pay for that extra quality. If you do not need to chip wood, you generally can get by more inexpensively buying a leaf shredder.
If you do not have a wood chipper or leaf shredder and do not wish to buy either one, just run your lawn mower over your leaves to shred them. Not only is this a cheaper alternative (since you already own the mower), but, if you have a bag on your mower that collects grass clippings, you do not sacrifice any convenience.
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