To control unwanted plant growth (their not always weeds) around the 3 1/2 by 8 foot beds in our greenhouse we had a friend get a discarded pulp machine felt from the local pulp/paper mill. The felt is one piece that covers the entire 20 by 36 foot floor and was put down before building and filling the beds. Excess water from the beds can easily drain through the felt but plants can't grow through it. This material may not be available to everyone but those who have a pulp mill in their area should keep it in mind.