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My backyard has far too much grass. I'd like to turn a fairly large portion of the lawn into waterwise beds and also expand my backyard vegetable garden. Two years ago, I made some beds by removing the turf. However, it is not only very hard work but it also results in a large amount of excess sod, and takes a good amount of topsoil with it. It also seems wasteful to send it to a landfill. Is there a way to kill the grass without herbicides? For example, will covering it with black plastic be an effective way to kill the grass? If so, how long will it be before I can plant in the new beds?

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A

Solarization is an option, but clear plastic works better, temperature under clear plastic actually gets hotter and works better to kill grass - this works best in early summer when grass is actively growing and temperatures are warm enough.  It's important the lawn is well watered prior to covering with plastic. It will take 8-10 weeks to kill grass this way.  Then the dead grass will take time to decompose - so as it decomposes, any nitrogen in the soil will be first used by microbes decomposing the dead grass.

Here is a link to article from Oregon State on Solarizing, click on http://extension.oregonstate.edu/news/story.php?S_No=172&storyType=garde


Another option is to build up layers of cardboard and compost- a minimum of six to eight inches over the existing grass.  This is best done in fall, and by next spring, with snowload, you can plant directly into these top layers of compost. The following is an excerpt from University of Illinois article on layers or lasagna gardening.

In a nutshell, you layer organic materials, starting with a 1-inch thick stratum of WET newspaper or cardboard laid directly onto established grass, overlapped slightly. Or in my case, a weedy flower bed. This smothers grass and weed growth and encourages our friends the earthworms to move in. On top of this layer, add 1-2 inches of peat moss. Then choose from the smorgasbord below, alternating strata of carbon and nitrogen products with peat moss between each layer, adding a sprinkle of wood ashes or bonemeal.

Carbon

Fallen leaves (except for oak), peat moss, straw, newspapers, cardboard or shredded paper, chopped stalks or chopped corn cobs, old straw

Nitrogen

manure ,blood meal, grass clippings (2 inches or less), kitchen waste such as leftover vegetables, fruits, eggshells, coffee grounds. NOTE: Avoid meats, oils or dairy products.

Your goal is to create 24 inches of material. This will eventually settle down to 6
inches of easily workable soil. If you like, you can outline the bed with landscape timbers, but that's not a necessity. Fall is the ideal time to begin this, so it can steep over the winter, but you can create your lasagna any time during the year. To speed up the cooking process, cover with a sheet of black plastic weighted down with bricks or logs. In about 6 weeks most of the layers will have broken down into a dark, crumbly material that's a joy to plant in.

The great thing about lasagna gardening is that you don't have to wait to plant – you can build the garden and plant it all in the same day (assuming the weather is warm enough). To make a planting hole in a new bed, simply pull the layers apart with your hands. Set the plant in the hole, pull the mulch back around the roots, and water it thoroughly.

To sow seeds in a newly-built lasagna garden, spread fine compost or damp peat moss where the seeds are to go, then set the seeds on the surface. Sift more fine material to cover the seeds and press down.

Posted on 14 May 2009

Maggie Shao
Horticulture Agent, Salt Lake County

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