In any modern urban landscape there will be weeds. This photo shows a typical Tri-Met, contrived, landscape with its simple massing and sweeps. It also shows weeds. Maintenance staff must have a standard, a threshold for action, what do they leave, when do they act. Aesthetics is the major criteria in this type of landscape for determining action and timing. The photo shows how disruptive the color and texture of weeds can be, how they interfere with the designers intent. Of course you must be careful with this because, for example, one stem of Canada Thistle, such as the one in the foreground, may be no big deal, but leaving it, allowing it to establish can result in larger problems down the road. You have to be very careful with perennial weeds when weighing this.