Sheet Mulching Assessment

(Originally published on Blue Boat Home, 4/27/2009)

The most common question that Jessie and I got about our house during the winter was, "What exactly are you doing in the front yard?"  They'd never seen anyone intentionally bury the yard in 6-12 inches of leaves before.  Here's what we were doing, and why, and what worked and what didn't.

As I described in "The Best Laid Plots," we first built a sheet mulch in the back yard (right) before learning that the entire back yard would have to be excavated for a new sewer line.  Curiously, although we're now rebuilding the plot in more or less the same spot as before (left), it's actually more work the second time because we have to move all the clay subsoil out of the way.  It's not nearly so picturesque right now as it was last fall, let me tell you.

Anyway, when we dismantled the sheet mulch in the back yard, we rebuilt it in the only place we could, which was the front yard, much to neighbors' consternation.  My father was very sad that I planned to kill some 200 square feet of zoysia grass since he's worked so hard to establish it in his own lawn, so I tried to find someone to take it away and transplant it, but got no takers.  Oddly I didn't get any pictures of the way it looked all winter, so I can't share that with you.  It looked a lot like the picture above right, only wedge shaped instead of rectangular. 

For those who aren't familiar with sheet mulching, my goals in using the technique were

• to loosen and fertilize the soil without tilling it, enlisting the labor of earthworms.  Tilling is arguably bad for anyone's soil structure, but particularly in clay soil like ours it can lead to clumps that plants find hard to work with, while worms break the clumps up.
• to smother and compost the grass and lawn weeds that were previously on the spot and would compete with the garden plants
• to keep the soil life warm during the winter so they could keep tilling year round
• to use local yard waste (grass and leaves) as fertilizer and herbicide rather than bringing in inputs from off-site

An arc of plastic edging separates the front garden bed from what remains of the front lawn.  We only dug up and overturned the grass around the edges; all the rest of the grass had a thick layer of (wet) cardboard and newspaper covered by grass clippings and as much as 12 inches of dead leaves which neighbor kids helped us collect.  We went ahead and planted a pear tree, three raspberries, three strawberries, garlic and potatoes and some herbs and comfrey by punching holes through the cardboard.  (Interestingly, all of these plants survived the winter, with the exception of rosemary.)  A border of poultry netting (chicken wire) held the leaves in nicely and kept us in compliance with local ordinance.

By February, the layer of cardboard was gone.  Completely gone, no traces left except a few odd edges.  Big fat worms were busily tilling the soil, which had become soft and measurably more fertile than the back yard (right).  We tried planting a few seeds but couldn't get them to germinate because the ground was still so cold.  Because of that, and because the dead leaves were looking a little tacky and we were tired of the poultry netting bulging out into the sidewalk, we removed what was left of the leaves.  When a late frost threatened, we used straw and a rowcover to protect the plants.  The photo at left shows an intermediate step -- part of the leaves and poultry netting are gone, and some straw has been added.  The rowcover helps to keep the wind off, so it's useful in frosty weather, and in warmer weather it helps keep the rabbits and bugs off.  We bought it for the back yard -- it looks tacky in the front, but extreme measures were called for on that day!

Now, when I worked on a permaculture-inspired farm in Iowa, moving the excess mulch aside in the spring was a trivial matter -- we just raked it off the rows onto the paths, because we had at least as much path as row, and traffic in the paths trampled it down to nothing.  But i cleverly designed this bed on a keyhole design to have the minimum amount of path, which meant that there was noplace nearby to put the mulch.  So all 150+ cubic feet of leaves had to be moved to the back yard, which as you might imagine took a few hours.  So much for no-work gardening, huh?  But at least the rings of fencing we made last fall (left) came to the rescue again: when filled more than halfway, the leaves compress under their own weight, so the large volume of leaves only filled two of these rings halfway, and we still have plenty of leaves to use in the backyard bed.

Uncovering the ground let the ground warm up, all right, and all the seeds germinated in short order, and the front-yard garden is off to a good start.  But the grass was not entirely dead yet, and removing the mulch revived some of it.  Since I had assumed it was dead, I planted right through it, so now I have my work cut out for me untangling the fragile young vegetables from a mat of zoyzia thatch.  We'll see how that goes!

So in review: The mulch was a success in that it encouraged the soil life to loosen and fertilize the soil all winter.  It smothered most of the grass and used local yard waste as a resource.  But there are a few things I would counsel others to do differently:

• If you are starting from lawn, leave the mulch in place 6 months or longer to ensure the grass is good and dead before you plant seeds.
• If aesthetics are likely to be a concern (e.g. in the front yard), seriously consider what you will want to use for mulch in the long run before beginning your sheet mulch in the short run.  (Straw does not look as good as we had anticipated.)  Consider where you will take the initial mulch when it's time to warm up the soil.

Aside from those two caveats, we're very satisfied with our little experiment, and now the neighbors are asking what we're growing instead of, as one boy asked at Halloween, "Is there somebody buried in all those leaves?"  That's gratifying.