I didn't: I let the grass grow on top of my boots.
After a whole summer of seeds apparently collecting in amongst the laces of my trusty Timberlands, it only took one rain event, followed by sunshine, to bring forth a small crop of miscellaneous vegetation. These old vineyard boots were destined to be retired anyway (I don't normally leave my boots outside), so there is no pressing need for me to mow my impromptu, mobile cover crop.
The same opportunistic weeds take advantage of the first available moisture every year. It's just that this is the first time I have seen it happen on an article of footwear.