Wednesday, December 3, 2008

Sheet Mulching

I don't like grass. I really don't like grass in my garden. Unfortunately, the lot began as a grassy area. More generally, the Willamette Valley is home to the grass seed capital of the world! So, it often seems that I've got a fight to the death on my hands.

One of my best weapons in this epic struggle has been 'sheet mulching'. For the most part, it works pretty well, though it's not a panacea.

Sheet mulching is simple: you wet the grass, put down a layer of cardboard, add a few inches of soil or manure, and then top off with at least a foot of leaves. Clearly it's a thing most easily done in the fall.

Last year I sheet mulched the blueberries and artichokes in the traffic strip on the north side. It worked fantastically...even without cardboard in some cases (just used extra leaves). This fall, we busted out with a huge sheet mulching effort in what will be the largest area of cultivation in the garden. We covered about 1200 square feet by schlepping in five pickup loads of manure, lots and lots of big cardboard, and about 10 loads of leaves we scavenged from the neighborhood. I'll post a picture of this soon for those who get silly about staring at manure and leaves!

This will be somewhat of an experiment owing mainly to the presence of a particular species of grass here which has super tenacious roots. I've found that sheet mulching mostly works if I attend to the borders of the mulched area by digging all of the grass out where the mulching ends. Failure to do so usually allows the roots to re-invade over time. In all cases, some maintenance is required and mulching needs to be done each fall to keep airborne or otherwise seeded grass from encroaching.

I leave the mulch on for about four months or so and then simply apply soil over the top to create a new garden. I do not remove the leaves. They simply rot away to compost, resulting in a really nice and loose bed.

In permaculture terms, my interpretation of what's happening with my successful blueberry-artichoke mulched bed is that the leaves basically replicate what happens on a forest floor. Grasses and other annuals are supressed by leaf fall from the canopy. In my case, I just bring the leaves in since I don't have enough tree cover to provide it on site. The effect is the same.

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