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GardenSMART ::

Sheet Mulching

By Therese Ciesinski, GardenSMART

Right now my back garden looks like an explosion in a cardboard factory. Sheets of the brown stuff lay all over the small yard, topped with the winter detritus from my perennial beds. I'm in a race against time and weeds, trying to turn an overgrown, hard-to-mow mess into a tranquil shade garden before the Japanese stiltgrass germinates and swallows the yard. My solution for making planting beds and paths is to sheet mulch.

What is sheet mulching? It's the process of smothering vegetation by covering an area with flattened cardboard and/or newspapers, then topping it with compost, soil and mulch in layers thick enough that the grass or weeds are deprived of light and can't germinate or grow. Plants are planted into the layers of soil and mulch. Over time the cardboard breaks down, but all those layers keep the weed seeds below from sprouting. It's an alternative to digging up or tilling the existing ground, which encourages weed germination.

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Sheet mulching isn't difficult. It just requires plenty of cardboard and newspaper. Here's how it's done:

Prep the cardboard. Stick with ordinary brown cardboard boxes, the bigger the better. Appliance boxes are the best because they cover the greatest area. Don't use boxes that are glossy or have shiny inks. Remove all packing tape; it won't break down and it's not good for your soil. Once the cardboard gets wet, I find the tape is much easier to remove.

Gather materials. Be sure you have enough cardboard/newspaper, soil, compost, and mulch to cover the area. If you use newspaper, have enough to layer it five or six sheets thick, with overlap. Measure the space and figure out how many cubic yards of soil, etc., you'll need. There are feet to cubic yards converters online.

I'm adding organic material over the cardboard and before the soil. The leaves, twigs, clippings, old mulch, etc. that came up when I cleaned my garden beds goes on top of the cardboard, as does the potting soil from last year's container garden. I'm not in a rush to plant, so it has time to break down. A chipper shredder would be handy in this instance, as smaller pieces disintegrate faster.

Be sure the ground is wet. For the cardboard to disintegrate, the soil beneath it should be wet. Either hit it with a hose or wait for a good, soaking rain.

Start layering. Lay the flattened cardboard right over the grass/weeds. Be sure each piece overlaps by at least six inches, or light will get in and weeds will squeeze up through the cracks.

Top with soil and rake smooth. I'll be planting a lot of perennials that require rich, moist soil, so I'm going with a soil and compost mix six inches deep.

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This is my backyard renovation project. I'm turning a scraggly lawn and a weed- and ivy-covered hillside into a shade garden. The sheet mulching project isn't finished. No, it's not pretty, but it will do the trick.

Mulch. It's important to top the bare soil with mulch ASAP, so weed seeds don't blow in and germinate in the new soil. Make it at least two inches thick. Shredded bark mulch, pine straw, and other materials that break down and nourish the soil are best. Mulch should be added every year thereafter.

Plant. Small plants can be planted right into the new soil/mulch mixture, on top of the cardboard. For larger plants, such as trees and shrubs or large perennials, punch a hole in the cardboard and plant into the ground below. The idea is to expose as little of the original soil as possible.

I still have to outline where I want the pathways to go. Instead of spreading soil over those areas, I'll top them with four inches of mulch and pine needles, but I could also go with pea gravel or another non-biodegradable material, which requires less maintenance.


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