Lawn into garden

If you want to convert some of your lawn to a garden, the obvious first step is to get rid of the grass. This is easier said than done with Couch and Kikuyu. Any pieces of runner left in the soil will re-shoot and become a pest in your garden beds. Lawn grasses are perennial, which means they are long-lived and able to regrow from stored nutrients after a period of dormancy.
All green plants require sunlight, carbon dioxide and water to manufacture glucose that they use for energy, and we have to deprive them of these in order to kill the grass without using poisons. You can exclude light with pieces of thick cardboard, a very thick layer of mulch, or a sheet of black plastic. I’ve found black plastic works best because it absorbs heat and speeds the process. Clear or white plastic won’t exclude light, and can actually increase growth in some conditions. The light-excluding cover will have to be weighted around the edges with some stones or scraps of timber.
Now comes the most important step. Go around the outer edge of the plastic with a sharp spade and cut through the grass runners. If you don’t do this, the runners outside the plastic can keep supplying water and glucose to the covered grass, and it won’t die off.
The time taken to kill the grass will vary according to the climate. In warm, dry conditions it can be completely killed off in 4–6 weeks. The dead grass and roots will break down to provide valuable organic matter to soil.
Avoid using herbicides to kill the grass. Recent research published by the US Department of Agriculture has shown that glyphosate can stimulate the growth of Fusarium Wilt pathogens in soil. This disease can affect many food crops, and is difficult to eliminate once established.