Ask Mr. Smarty Plants

Like kissing a porcupine, very carefully. Okay, sorry, we'll get serious. First rule, NO SPRAYS. Whatever you read on the label about how safe an herbicide is, it is not safe to spray it. The spray can drift or simply fall out of the air somewhere you did not want it. If, indeed, what you have is grassy weeds, that is, monocots, with long slender leaves that have parallel veins in them, there are specific herbicides for monocots. But you still don't spray it. It probably wouldn't kill the cactus if it drifted over onto it, but it wouldn't do the cactus any good, either. Try to find a bottle of liquid monocot herbicide. And remember your lawn is probably a monocot grass, so don't get careless with the bottle, either, Get a long-handled artist's brush, a cheap one, because you will have to throw it away. Dip the brush into the liquid monocot killer, and then paint the grasses. The nearer you can get down into the root area of each grass, the better, because it is the root you are trying to kill.

Alternative, or perhaps supplemental, method. Get what we used to call a sharp-toed hoe. This was a regular, long-handled hoe, but the blade was triangular with a sharp point. Surely, this is still around in hardware and garden supply stores. Remembering to protect your hands with leather gloves, and your body with heavy clothes, dig out as much root from each weed as you can and remove it, with the hoe. Don't leave it there, because many grasses have stolons, or underground stems, from which new plants can grow. After that, keep a close eye on the patch of weeds, treating anything that pops up with the herbicide or hauling it out with the hoe.

And we think the job should be given to whoever had the idea for a cactus garden.