This time of year you see a lot of “eco-friendly” gardening advice about dead leaves and I wholeheartedly endorse the bottom line - that it’s crazy 
to send them off to the local landfill, where they take up space and waste all that organic matter. But the next part of the advice - what to do with them instead - well, that’s where it starts to get complicated but hey, that’s gardening! Let’s dig in.
On the lawn
Nobody seems to think that whole leaves should be allowed to remain on lawn because they can smother turfgrass. Many experts suggest instead that we run over them with a lawn mower and let the chopped-up leaves stay there as a source of organic matter and some nutrients for the turfgrass. That’s great advice and don’t worry - it won’t cause or contribute to a thatch problem. (Thatch is usually caused by overfertilization with synthetic fertilizers). Some brand new research proves that chopped leaves not only add organic matter and nutrients – they even suppress weeds! Here’s the story.
However, some folks consider any use of a gas- or electric-powered lawn mowers to be an unsustainable gardening practice for obvious reasons - the fossil fuels involved (either gas or the coal required to produce electricity). But lawn mowers are a topic for another time - a very hot topic these days. So moving on, if you do remove leaves from your lawn or anywhere else, what do you do with them? See composting below.
In the vegetable garden
This situation is a simple one. Leaves that fall on an emptied vegetable garden can be left in place and then turned under in the spring, after which they’ll decompose quickly, adding organic matter and some nutrients to the soil.
On hard surfaces
For obvious safety purposes, dead leaves should be removed early and often from surfaces people walk on. And certainly all wood surfaces benefit from having the leaves removed to prevent rotting.
In the flower and shrub beds
What to do about leaves on and around our ornamental beds and borders is where the hot-under-the-collar arguments really take place. (Yes, gardeners are an opinionated bunch.) Though everyone does agree that chopped leaves are great in the beds and borders as an organic mulch, and for more about chopped-leaf mulch, check the Illinois Extension Service.)
But whole leaves? Well, it depends - on how many leaves, what type of leaf, and which groundcovers those leaves are covering. To get personal, about 50 trees drop their leaves on my garden, most of them large oaks, and these masses of large, whole leaves can mat down and smother my groundcovers, or at least create a barrier that would prevent rainwater from seeping through to the soil. And oak leaves simply don’t decompose over the course of the winter, so I’d have to collect them in the spring anyway, so why not do it now? I rake up about 80-90 percent of them in December when they’ve all fallen, and I do the fine-raking and hand-picking in the spring when I’m cleaning up, mulching and generally prettying up for the new season.
But not everyone agrees about this. Syndicated columnist and Maine gardener Barbara Damrosch writes that “Most ground covers…benefit from a weed-smothering leaf mulch - once winter has matted it down a bit - and will come up happily in spring. I let leaves collect in perennial flower beds, too, removing them carefully with a narrow, springy metal rake just before spring bulbs poke up. They can be gathered for the compost pile.” But Barbara, how come they smother just the weeds and not the desirable plants, your groundcovers? Could be that your groundcovers are unkillable, like English ivy and Pachysandra, while I’m talking about more delicate ones like Pulmonaria and Ajuga?
So here’s where I come down: If you have just a few leaves, or if they’re thin like elm leaves, then they probably won’t do any harm and will decompose by spring, so go for it - if you like the look. Yes, appearance, pure aesthetics and nothing more - is another reason I remove most leaves in the fall - because I’d rather see even semi-evergreen groundcovers than brown, dead leaves. Gardeners in colder climates may be looking at snow cover from Thanksgiving until May, so they laugh at the very notion of seeing their groundcovers over the winter.
See how many variables are at play here? And why it drives me crazy to see gardening advice that assumes all gardens are the same!?
Composting dead leaves
Now if you DO remove any or all of your leaves, what should you do with them? Everyone agrees that they make for some mighty fine homemade compost, especially if you combine them with some green matter like lawn clippings for a nutritionally complete result. But there’s disagreement about whether whole leaves compost well and here I’ll weigh in. My compost method (such as it is) is to simply pile the leaves up and wait a year or more for them to decompose. The problem is they never DO decompose completely because I never water or turn the pile. (Breaking all rules, I know, but turning is hard work.) But no matter – I use the resulting so-so “compost”, containing some noticeably uncomposted chunks, in out-of-the-way spots as mulch, or to amend the soil.
But if you want to turn dead leaves into quality compost it’s much better to chop the leaves first, and I did that for a whole season a few years back. I bought a cheap filiment-style shredder for about 100 bucks and ran all my leaves through it. But because it was a cheap, flimsy machine, the Weedwacker-type filament broke with every twig and acorn it encountered, so every five minutes or so I had to stop and replace the filament, and the chopping process became a super headache. If I’d spent more on a chipper-shredder the work would have gone quickly, but I judged $1,000+ to be too steep a price for faster, more uniform compost. Of course I could have spread all the leaves on the lawn, then mowed them with a mulching mower (one with a bag to catch the cuttings) but that sounds to me like a whole lot of work to me.
The Rutgers Extension Service has good information about composting with dead leaves - check that link. They offer a tip I hadn’t seen before - adding Nitrogen to the compost bin to speed up the process.
If you don’t have space for a composting operation, your city or county may have the answer - or will soon if enough residents ask for it. About 20 years ago local governments across the U.S. began prohibiting the dumping of green waste like leaves and creating programs to collect and compost yard waste for their residents. As a result, they make good use of all that organic matter, save the money they used to spend on landfill fees, and save even more money because they’re using their own homemade compost on public land instead of buying compost and fertilizer products.
Below you see the city crew picking up leaves on my street, and the resulting mulch pile delivered to my driveway the following spring. 
Top photo credit.
