Weeding beds will always be a continuing, ongoing, constantly repeated part of landscape maintenance – even when effective control methods are being utilized.
Glyphosate is generally effective in killing actively growing weeds. Where it can be used without affecting desirable plants is better than hand weeding in the case of perennial weeds as it kills the roots. If you see a week after spraying that the weed still shows some life, spray it again.
But, this will have to be done as needed. Even if you successfully kill every grassy weed in the bed – it will come back at some point. If it found its way into your beds before, it will certainly do so again. And, when it does, you have to spray again as needed.
1) Keep the beds well mulched 2 to 4 inches thick. A thick mulch is the best defense against germinating weed seeds. In some situations, depending on the weed, putting down a weed barrier/landscape fabric under the mulch enhances weed control. Do you know the identity of the weed you are dealing with?
2) Roundup is the premier brand of glyphosate. You pay dearly for that brand name. Your weeds, however, are not at all impressed by the name Roundup on the label. There are much less expensive formulations of glyphosate that are just as effective. Be an aware consumer and comparison shop at the nursery. Check out the other brands like Killzall, Kleenup, Grass and Weed Killer and others. As long as they contain glyphosate, they are the same thing. This will save you some of that money.
Consumer Horticulture Specialist
The LSU AgCenter and the LSU College of Agriculture