Rake Leaves and Make Compost, Mulch

Sorting the Leaves You Rake Into Compost Bins, Mulch Bins

Image showing maple leaves that have fallen on a lawn.
The fallen maple leaves on this lawn looked great when they were still on their trees but must now be removed. David Beaulieu

The landscape maintenance task that is practically synonymous with fall is raking leaves off the lawn. Aesthetics aside, this chore can be necessary, since a thick layer of unshredded leaves left on top of your lawn over the winter could smother the grass below. If you will be saving the leaves you rake to be used in some capacity in next year's landscaping, it is important to be clear in your mind about that capacity before you rake your leaves. Will you make compost with them to be used as a soil amendment, or will you make mulch with them? What's the difference, you ask? Please read on.

To make compost with leaves is a lot of work. You can't just throw them into a pile and expect them to transform into a wondrous black humus ripe for next year's landscaping needs. The ingredients in a compost bin should be properly mixed and watered, and the layers of the pile need to be swapped around in a process called "turning over" the pile.

Leaves will decompose into compost more quickly if they are shredded before being placed in a compost bin. Leaves can be shredded simply by running a mulching lawn mower over them. Once thorough decomposition is achieved, the compost still needs to be housed in a bin of some sort, to protect it from the elements that would rob it of its hard-won nutrients.

Beginners often confuse compost and mulch. The confusion is understandable since mulch eventually breaks down and becomes compost in its own right. But although compost and mulch are related, they are nonetheless distinct and serve two different functions.

Organic matter can function as "compost" only after it has thoroughly decomposed, enabling it to release nutrients into the soil. But when leaves are to be used as a mulch, they should not be thoroughly decomposed. A mulch serves not only as a weed suppressor but also as a barrier between your soil and the heat, cold and wind from which you want to protect it. The mulch barrier lies exposed on the soil surface so that your soil doesn't have to. When leaves have thoroughly decomposed, they're less effective as such a barrier. It is somewhat wasteful to employ decomposed leaves in such a manner since the nutrients they harbor should be protected for use underground (by plant roots), not exposed to the elements. It simply makes more sense to let non-decomposed materials do the rough-and-tumble work of serving as barriers.

Consequently, leaves that you'll be using for mulch should not be tossed into a compost bin, but kept in a separate "mulch bin" of their own. Like their compost bin comrades, however, it is best to shred the leaves destined for the mulch bin. Unshredded leaves pack down and prevent air and moisture from reaching your soil (see "anaerobic composting"). Shredded leaf mulch has less of a tendency to pack down. It takes a while to turn leaves into compost, but leaf mulch is ready to be used as soon as you shred it.

Leaves in a mulch bin will be treated differently from leaves in a compost bin. For mulch, a bin is merely a holding tank. Unlike the contents of a compost bin, you are not trying to hasten the decomposition of the leaves in a mulch bin. On the contrary, you'd prefer them not to decompose. For, once they decompose, they're no longer mulch -- they're compost. And as compost, they can no longer carry out one of the main functions of mulch, which is to suppress weeds. In fact, weeds will grow...well, like weeds, if given a layer of compost in which to reside. Perhaps no other point so clearly highlights the difference between compost and mulch. To learn more about mulching options and considerations, see Selecting the Proper Garden Mulch.

To Rake Leaves or To Blow Them?

The question of whether you should rake leaves or use a leaf blower/vac is answered in my article, How to Use Leaf Blower/Vacs. Since many people will end up using both a rake and power equipment, the question often comes down to when it makes sense to use the one, rather than the other.

Compost Bins, Mulch Bins: Eyesores?

Finally, a word about the appearance of your compost bins and mulch bins. After all, the bins themselves become a part of your landscape and, as such, surely cannot be said to fall outside the scope of aesthetic considerations. But since you need access to the organic matter of a compost bin in order to turn it over, there is less leeway for aesthetically pleasing designs here than in the case of mulch bins (practicality ultimately trumps aesthetics). But the latter certainly can be constructed with an eye to aesthetics. You have fewer restrictions with mulch bins since all they have to do is sit there and hold next year's mulching material in place. So be creative.