Make a new garden bed on a grass lawn.

Garden bed (raised) made over grass lawn.
A grass lawn can become a fertile vegetable garden bed without removing the grass sod or tilling the soil. This is achieved by smothering the lawn with cardboard layers to deny light and kill grass and weeds, but still allow the moisture required to decompose the grass into fertile compost.

This method takes time. The longer the bed rests under the cardboard, the better. The cardboard should not be removed until the grass is fully dead and composted, and weed and grass seeds have germinated and then died from lack of light.

In a northern climate, where composting is slow, this process can take a full growing season to ensure the grass and weeds are dead and composted. Be prepared to wait a year.

Once the snow has melted, before grasses and weeds have started growing, select the site. The new vegetable garden bed is best located in a sunny spot, without tree roots that clog the soil and steal moisture and nutrients. While the bed dimensions can be any length, the width is best kept to no more than 4 feet, for ease of access without stepping on the bed.

Mark out a border pathway around the new garden bed of about 18 inches on all sides. This is to protect the garden bed from creeping quack grass. This border will be covered with cardboard too and later become the path around the bed.

Prepare the bed by picking off by hand obvious weed seed pods. Mow the grass and mow down any weeds. The plot should be mowed flat. No need to rake. If dry, water the soil to get weed and grass seeds to germinate and force perennial weeds out of dormancy.

Collect plain cardboard boxes. Flatten them to single layers. Collect enough to cover your plot (plus the 18 inch borders) in a double layer, triple is better.

Place the first layer of cardboard over the plot and over the borders around it. Lay another layer or two of cardboard on top and cover any openings. Hold the cardboard down securely with heavy rocks, bricks or boards. No light should pass through. The layers of cardboard need to last in place a full year.

Leave the cardboard on all summer and winter, until the following spring. At next seasons planting time – after the last frost - remove the cardboard. 

The grass will have composted into black humus. If the grass was growing in clay soil, the soil can be lightened with more compost and leaves.

This methods works well if building a raised bed on the new plot. Fill the raised bed with good garden soil on top of the new bed.   

We place bark mulch on the paths around raised beds that are not tilled. Wet cardboard is too slippery for pathways. You can put the cardboard under the bark mulch and the paths will be weed free- for a while anyways.

Garden bed previously grass.