I have a ~16 ft planter box that becomes filled with what I believe to be sudangrass. I have tried Roundup, I have tried boiling water. I would like to eventually plant vegetables, but want to rid the box of this first. Any suggestions?
Sudan grass/Johnson grass are in the Sorghum genus. They are difficult to control. For your planter size, Extension publication suggest hand pulling including removing as much of the root system (rhizomes) as possible. These plants will produce new shoots from the root system.
Another suggestion is, what you have tried, using a Roundup. This may require multiple applications. As with any chemical, read and follow directions carefully.
You may contact me directly at the Jefferson County Extension Office 502-569-2344.
ANR Agent/County Coordinator.
Jefferson Co Extension Service
810 Barret Ave.