There is also an event
Click to reveal..
where someone fertilizes your yard and weeds pop up everywhere.


But if you really want to generate socks/wrappers/dirt smudges/weeds...
Click to reveal..
Let them sit around for a day or two. It seems the more there are the faster they multiply. I went away for the weekend and had the house clean for one family and didn't for the other. When I got back, the house that was a little messy was a whole lot messier than the house that was clean to start with.