Kyler; you want two things for a good kill-off with herbicides:
- good leaf surface to affect the spray (usually a minimum of 5" tall for weeds)
- actively growing plant (usually spring or fall)

This combination will give you the most for your money. Roundup will work at other times but you may need higher rates etc. The instructions with the Roundup will tell you what the proper growth stage is to spray different plants.

Dan O.