Answer: It's amazing how annoyingly tenacious weeds can be! If the weeds you're dealing with are perennials that spread from runners or stolons along or below the ground (e.g., Bermuda grass or nut grass), you'll need to pull them out and mulch heavily under the ground cover with organic matter such as wood chips. You can keep cutting them off to keep them under control, but they usually pop up elsewhere. Herbicides probably won't work in your situation, because the weeds are intermixed with your plants. The herbicide won't distinguish between the plants you want vs. the plants you don't!
If the weeds in your groundcovers are coming up from seed, then you might want to try corn gluten. Corn gluten produces
an enzyme that inhibits seed germination, and can be used as a preemergent herbicide. You can get it from Gardener's Supply Co.(www.gardeners.com; ph# 800/863-1700); they call it WeedzStop. However, if your groundcover is something that reseeds itself annually, this product would inhibit that also.
You might want to try giving the area a slow soaking of water to soften the soil. Then the weeds will pull more easily. Of course, the water will germinate more weed seeds, but then you pull them ASAP. If you keep at it steadily for several waterings and several heavy-duty weeding sessions, you may be surprised at your success. Regardless, always pull weeds before they go to seed. One of the reasons they survive so well is that they produce jillions of seeds! (You might have a "contest" for neighborhood kids after soaking the area. Grand prize for the one who pulls the most buckets of weeds, pizza for everybody, etc.) Good luck!
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