Yesterday I happened to see a garden calendar encouraging people to pick up their leaves so that they don’t pollute streams and lakes by encouraging algae to grow. This was a good idea, I thought, but then I started to wonder whether leaves on the lawn might not be a better idea? After all, the reason that leaves cause algal growth in water is because of the nutrients they have. And if they have nutrients couldn’t those be used for fertilizer instead of the regular fertilizers which we use? What if we raked all of our leaves onto our yards?
There’s no denying that leaves which drop in the fall can make great compost, but how well would they work as a fertilizer? So I did a little bit of preliminary research — reading old papers and such — and here’s what I’ve come up with:
Fallen leaves are very variable in nutrient content. Some leaves have 1% nitrogen, and some can have almost 3% (these are mostly from leguminous trees). In terms of phosphorus, fallen leaves tend to have around 0.1%, though once again, it’s very variable. For the purposes of this post I’m going to stick with nitrogen.
For 1,000 square feet of grass yard it takes about a pound of nitrogen per year to fertilize, even with a low input variety.
In a heavily wooded lot it wouldn’t be odd to have around 100 pounds of leaves fall in a 1,000 square foot area. At 1% nitrogen, the leaves would provide enough nitrogen for the grass, but that would probably end up being a moot point because the leaves would have a good chance of smothering the grass.
So what I’m wondering is, if we planted trees which were legumes, and had higher levels of nitrogen, and if we chopped up the leaves so they weren’t as likely to smother the grass (using a lawnmower or whatever) could we provide enough nitrogen per year for a healthy low input lawn? Personally, I think so. We would need to keep these leaves off of driveways and sidewalks because this is where they would do their worst in terms of contaminating water, but if they were just in yards — I think it might work.
Jeff, that’s kind of what we did in Buffalo with all of our maple and oak leaves. We had a leaf shredder that was a giant funnel with a string trimmer mechanism at the bottom that sat on top of a wheelbarrow or garbage can. But we put the shredded leaves on the garden beds to protect the plants – about 4″ thick. Shredding kept them from matting, which is a problem for water and gas movement, and they broke down quickly in the spring. We never fertized our beds. Turf of course is more nutrient-hungry, but I don’t think we fertilized it either. It was well-colonized with violets, thyme, primroses, etc. The only lawn that I truly loved and enjoyed and rarely had to do anything to it but mow.
I went to a talk by an Epimedium grower a few months ago and they blow the leaves off the beds, mow them, and then blow them back into the beds.
I’m so glad to see this, and I hope you might talk, er, write about this some more in the future. I was talking to a fellow newbie Master Gardener yesterday evening. She was saying she needed to get her (rather few) leaves raked up before the snow hit later on this week. I told her I used my mulching mower earlier this week to finely chop the leaves (lots and lots) on my lawn. I figure the more organic material I can get into my poor soil, the happier my plants and grass will be.
She was concerned about thatch accumulating from this “lazy habit” of mine. Thatch is one of her greatest fears in live, but I’ve never had a problem
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with thatch, at least that I know of, so I kind of shrugged it off. We didn’t care so much about not agreeing with each other, but we were wondering what we’d tell a client who comes into the plant clinic.
Any thoughts?
A comment on thatch:
Thatch is a sign of sick soil where microbial numbers have been decreased by using soil amendments that set back these soil building armies. healthy soil will break down matter such as thatch and chopped leaves. If you have the signs of low microbial numbers such as thatch build up it might be good to clean out the build up and compost it. however, the most valuable action would be to build up the numbers through such methods as compost applications, compost tea, or if you what to just purchase it “Turf Pro”
A gallon of this is not cheap but it will go a very long way in making your lawn soil healthy. the result of healthy soil affects disease pressure, weed pressure, and thatch build up.
Actually, thatch is a pretty normal occurrence when you let the grass grow a little too tall before cutting it. Natural microbial activity breaks it down over time, but it is a great idea to remove and compost it. The idea that compost tea will be useful to get rid of thatch isn’t realistic — if the ground can handle the proper microbes then they’ll be there. If it can’t then they won’t. To make your ground more welcoming to microbes adding compost is a great idea.
There is some science on this, from Michigan State I believe. Mulching equipment certainly shreds leaves sufficiently to leave them on the lawn with no danger of smothering the lawn. Advocates for leaf mulching mulch leaves on hard surfaces and blow them onto flower beds, or blow leaves off hard surface onto lawns and mulch them there. It is a fast, efficient, way to deal with leaves while reducing noise pollution from leaf blowers and restoring organics to the soil. It also greatly improves soil sttructure, which helps with turf grass growth. Check out http://www.leaveleavesalone.org
Fiona~ Thanks very much! I shared the link with my fellow newbie, so now we have a united response to share with others. I especially like the fact we can tell them that it’s perfectly okay to use a regular mower, and that they only need to get a special blade if they are green grass perfectionists.
Also thanks to whoever removed my double post for me–how embarrassing!
I wish more people dealt with their fallen leaves in a more environmentally sound way. I think the worst you can do is pile them into plastic trash bags and dump them in the landfill, yet that’s what most people seem to be doing. What a terrible waste of both leaves & plastic. Personally I just run over my fallen leaves with a mulching lawn mower which makes them nicely disappear into the grass/soil and it recycles the nutrients. I do the same with my grass clippings and I’ve never had any thatch problems.
At our Community Garden we beg our gardeners, if you MUST bag your leaves – bring them to us! We use these leaves in our compost bins, we scatter them on eroding hillsides and we use them as mulch around trees and in some of our garden beds. Leaves are awesome!
Likewise, on the local Patch blog I write, I have let it be known that I WILL be skulking around curbside on trash pick-up morning for the sake of stealing bags of leaves. And truth is, I do “steal” as much as my Volvo station wagon (affectionally known as the Volvo truck) will hold. Our town does not have a recycling program for leaves, so I’m just saving them from the landfill and giving myself lots of free goodies for the lawn and garden.
My evil plan is to appeal to people subliminally to get them to re-think the value of their leaves. (Hey – if she is going to all this trouble just to have leaves, maybe I should keep them)
This has been a rant of mine for years – I even wrote an article on the topic for Fine Gardening magazine in the fall of 2007 (http://www.finegardening.com/how-to/articles/improve-soil-rake-less.aspx?nterms=74874).
For more information on autumn leaf management options, go to the following section of my website, http://www.tlehcs.com/Special%20Topics/Leaves%20Arent%20Trash/lat%20introduction.htm.
I posted about this tangentially last November – check out VT turf guy Mike Goatley’s publication “Leave Them Alone”
http://pubs.ext.vt.edu/430/430-521/430-521_pdf.pdf
and there’s a podcast also…
I would love to see the research sited in above-mentioned articles. It is always fun to have some quantitative information to back up practices you’ve already been doing. Where I work as a groundskeeper, I also mulch mow and leave the chopped up leaves on the lawn. Where it is unacceptable to have leaves I put the bagger on the mower, drop the mower height if needed, and can mow leaves right up off paved surfaces. These chopped up bits go either in the compost piles, or directly to beds that need a little extra mulch for winter. It would be interesting to see some soil analysis of the nutrient difference (if any) between leaf mulched and non-leaf mulched areas. But nutrients aside, I’m all for making my job easier and not raking and blowing constantly all fall long! The only reason I would consider not doing this is if I had a diseased tree that might spread disease through fallen leaves.
I’d like to understand more about the science behind the polluting aspects of the leaves lying in curbs before pickup. IIRC, phosphorus is culprit here. There also is something different between fresh water lakes and salt water estuaries, like the Chesapeake Bay, in terms of natural nutrient deficiency that keeps algae blooms in check. Nutrient runoff changes that. Jeff has touched on it with his phosphorus and fertilizer posts in the past, but I’d like to understand better from the algae’s growth point of view.
I have to admit that I am a very lazy gardener. I do rake my leaves, but I immediately pile them up around shrubs for mulch — no chopping, shredding, or composting needed. I figure if it’s good for the forest, it should be good for the garden.
In the spring, however, I do scrape up any large piles of leaf mulch and put it in the compost, so the sun can warm up the ground that much quicker.
I find it funny that this calendar implies that leaves are pollutants.
I would love to read about the research on putting black walnut (or other allelopathic) leaves in compost piles.
I use a much more efficient system for my lawn. Here in Z6 southeastern NY I stop mowing my lawn towards the end of Sept so it is tall and strong enough not to be smothered by leaves, then I just let the leaves fall where they will and rot in place. Those on the driveway get crushed by vehicles and become tree mulch but the grass catches most of the leaves. I never rake, or blow over the lawn.
I’m in a sheltered area though, so the wind doesn’t clear off my lawn. The problem with shredding leaves is that it is another petro powered activity. If you are using a leaf blower to gather them it not only pollutes with exhaust but also with extremely annoying sound. In the toney neighborhoods where I make my living it is an endless cacophony. I would not want to live in a wealthy neighborhood- trying to maintain a pristine lawn is a horrendously loud and obnoxious pursuit in these places. Mow and blow, mow and blow at least once a week during growing season and then blow the leaves off the lawn once or twice a week with the most powerful blowers available when it stops growing until first snow.
Ray, in terms of the effects of the leaves it has to do with additional nitrogen and phosphorus getting into the water. Algae is usually limited by one or the other of these nutrients. When you add more the algal blooms become worse. More leaves on hard surfaces = more nutrients going into the gutter and eventually the water. Val — I haven’t actually seen much research on black walnut in compost, but from reports I believe that black walnut would need to be composted for quite a while before it could be used for anything.
Alan, I don’t like gas-powered lawn equipment either. So I use an electric lawn mower to both cut my grass and shred the leaves. No need for a leaf blower.
I just mowed my lawn – Nov 10 – to take care of the last of the aspen leaves from the weed tree behind me. I always figured that if a tree didn’t like leaves on its feet, it wouldn’t put them there. At least the larch needles are small (the next tree to lose leaves)
I am visiting in the N virginia area and talk about leaves!! Of course there aren’t a lot of evergreens and so many oaks whose leaves are so tough. They seem to be ankle deep in my son’s yard and think there are just too many and too slow to break down to make it feasible to leave on the grass.
Leaves causing pollution? Leaves are a resource. I’d be more concerned with the lawn care companies spraying chemical fertilizers, pesticides, and herbicides. How much pollution results from runoff of this activity?