You can start now! Proper site preparation gives your plants a great head start. Removal of competitive weeds and grasses must be accomplished before planting begins. One option: cover the area with 4-6 layers of newspaper or cardboard to block out sunlight. Saturate the newspaper or cardboard with water to prevent it from blowing away, then apply clean shredded mulch. A few weeks later, after the newspaper or cardboard has softened, punch holes in it and insert your new plants.