Answer
Round up does the trick and you can plant as soon as the weeds, etc are dead. It doesn't affect the soil, so you can feel safe in using it. Once it is clear, prepare the soil correctly, not hurrying the process. You then will be rewarded with lovely flowers and vegetables. We just re- landscaped our back yard, turning it over, and even sifting the dirt to get rid of all stones, etc. We then built 3 enclosed beds of soil, and have planted tomatoes. Herbs go in tomorrow and soon lettuce. We already have beans growing, and plan to have the entire back yard growing things to eat, or in between the raised beds, lovely flowers. We simply got tired of weeds, etc. and will have less work to do. We tried the black plastic but got impatient and wanted to start long before the grass would have been dead. When I say we, I mean my husband. He immigrated from Holland this year to live in the house I own, and so he brought all of his lovely skills from Holland. They sure know how to grow flowers and veggies over there. Good luck. It is all worth it. No shortcuts.