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.