When grass is left to grow around freshly planted seedlings, the grass will compete with the seedlings for vital resources, such as the nutrients in the soil and sunlight. Due to the fact that the grass will be more established and more abundant in the area than the seedling, the grass will often manage to steal enough of those resources to inhibit the seedling's growth. If you would like to kill the grass in the area around a seedling until the seedling becomes established, there are a few natural ways to do it.
Mow or till the area where you would like to kill the grass. This provides better access to the roots, which makes the grass die more quickly.
Smother the grass with plastic bags or a waterproof tarp. Colored material that no light can pass through will prevent both moisture and sunlight from reaching the grass, and the grass roots will die within a week or two.
Layer pieces of newspaper over the grass that you want to kill. Wet the grass before layering and use at least eight pieces of newspaper stacked on top of each other to thoroughly block out light and moisture. Cover the newspaper with mulch. The mulch will keep the newspaper weighed down as well as hidden. Newspaper will not need to be removed after the death of the grass, as it will decompose into the soil, adding nutrients to the soil, making it a prime location for future planting.
Spray the grass around the seedling with white vinegar. White vinegar works better in warmer temperatures, so this technique should be utilized on summer days.
Allow leaves that have fallen in the autumn to remain on the ground in the area where you would like to kill the grass. Water the leaves to weigh them down and make them denser. Like newspaper, fallen leaves will smother the grass roots and decompose, enriching the soil beneath.