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Sheet Mulching

Sheet mulching is a handy way to prepare a garden on an area where lawn is growing. It also works for dealing with weedy patches. It is less work than digging the lawn out but does take a bit of time, planning and gathering of materials.

In brief, what you do is cover the new garden area with newspaper to smother and kill the grass, and cover the paper with organic mulch materials to hold it down and to improve your soil. It sounds simple but you need to do it properly to make it work. Many lawn grasses are great survivors and you don't want them growing back up through your new garden.

Sheetmulching does not work with nut grass which can push its way up through almost anything.

Here is a step by step guide based on experience, observation and sharing ideas.

Prevent escape
Start by removing grass from places where it might escape from under the newspaper. Dig a shallow trench around the area where you want to put the garden. A spade's width and half a spade's depth will do the trick. This clearly defines the area and makes sure that there will not be any lawn creeping straight back into the garden, or any surviving lawn escaping out from under the newspaper around the edges of the patch and spreading through the garden. Take care of the entire outside edge, including where the garden will be alongside a fence, wall or path. Also remove lawn from around objects within the garden area, such as the trunks of trees, the stems of existing plants, (don't go too deep or you will damage these plants' roots) clotheslines, or anything else that creates an 'edge' for grass to escape.

This preparation is the hardest part of the job, but saves a lot of time and effort if it is done properly.

Weaken the Grass
Damage the grass. Cut and bruise stems and leaves. Chop down into it with a sharp spade. Flatten any weeds completely - you don't want any cut stalks left to break holes in the newspaper that you lay down later.

Sprinkle a nitrogen-rich organic fertiliser over the damaged grass. Bird manure (pigeon or chicken are easily come by) or blood-and-bone are good here. This encourages rapid soft growth of the smothered grass which dies quickly. These materials also promote the growth of bacteria which will help to kill the broken, bruised and over-fed grass.

You can also sprinkle soil-improving minerals over the area if you feel it is needed. Note - many chemical fertilisers are sold as 'mineral' mixes so read the information on the bag carefully before buying. Good organic gardeners are smart enough to avoid chemical fertilisers.

Water the area.

Smothering
Lay 'sections' of newspaper, eight to twelve (or more) sheets thick, over the grass. Be sure that all sections overlap each other on all edges by at least 10 cm. This is very important - you don't want grass escaping between the sections. Be methodical and cover the whole area evenly and with good overlap. This job can be tricky on a windy day. Wet paper will not blow away so if an extra pair of hands is available, take turns to hold a hose and lightly spray the paper as it is laid down. Doing the job alone? Sit your pile of newspaper in a wheelbarrow full of water before starting.

Do not use glossy paper, it may be toxic.

As a (very) rough estimate, a 30cm stack of tabloid newspaper should cover about 10m2 of garden.

Mulching
Cover the paper with mulch such as straw, seagrass, lawn clippings, weeds (without seeds), leaves (light sprinkle only), wool waste and manure (the two latter materials to go under other materials). Do not leave mulch up against the trunks of trees or the stems of plants, it can cause them to rot. A few well placed bricks can keep mulch away from tree trunks.

How much mulch do you put on? There are two strategies.

Strategy 1 - Shallow Mulch.  This is a long term strategy for the patient gardener, or for those who are unable to get more mulch. The mulch only needs to be deep enough to cover the paper and to prevent it from blowing away. No less than 10cm because the mulch can settle and with too thin a layer the newspaper can be exposed.

Now you need to wait until the grass underneath has died off, usually 1 to 4 months. Couch grass will go dormant during Winter then grow back in Spring, so you might have to wait longer.

When the grass under the paper is dead you have a garden ready to plant. Make holes about 10cm wide in the mulch and paper. Top up (don't fill) the holes with soil, compost, or ideally a mixture of both. Plant seedlings in those holes, then water and tend. Seeds can be planted in a similar way, with a long narrow trench for seeds, instead of individual holes for seedlings.

Strategy 2 - Deep Mulch.  If the mulch is 15cm or deeper, you can plant immediately. Make a holes (for seedlings) or trenches (for seeds) in the mulch 10 cm wide and 10cm deep. Do not break the paper. Fill with compost and/or soil, and plant seedlings or seeds in the soil/compost. Eventually the plants' roots will get through the newspaper. By this time the grass beneath will be dead and the garden flourishing.
If you have any questions to ask or comments to make about this guide, please do so in the forum