In act 1 scene 2, Hamlet uses the image of an unweeded garden to describe his world.
Hamlet is saying that most of the people in the world are either rank or gross.
The things that are "rank" in such gardens are the kinds of plants that do not grow tall but choke the flower beds and encroach on the walks, helping to create a picture of abandonment, failure and desolation. Lawns that are not mowed will either become dead and brown or else, if they can get enough rain water, will become thick and ragged-looking. The tangled individual plants will appear to be fighting for a foothold on the soil and a place in the sun.
In addition to the vegetation that is rank, there are some weeds that take advantage of the untended condition of the garden to grow to their full height and even develop ugly flowers. Such tall weeds are usually marvelously ugly and misshapen.
Hamlet is thinking that many humans who stand out above the masses are remarkably ugly
