We have quite a large garden in our backyard. What we learned over the years is that it is difficult to control the growth of plants and vegetation without having to micro manage them (trim leaves or remove unwanted growth). We just recently started this neat little trick of using toilet paper rolls to control the flowers before we move them to our garden area or just control the growth all together. Also I figure you can use this same technique with vegetation like lettuce where you do not want all the seeds in one location of the lettuce blocks more lettuce from growing and slowing growth. Give this idea a try and let us know how it goes.
Credit for Image(s): permacultureideas.blogspot.ca