Groundcover plants are typically low-growing plants with a spreading, trailing or mat-forming growth habit. Over time, depending on how far the plants are spaced at planting time, groundcovers will grow completely together to form a carpet or dense cover above the ground. Many grow dense enough so as to prevent weed growth. However, as groundcovers are growing and filling in, weed control might be necessary.
Start By Identifying the Weed
If you are unsure as to the type of weed(s), the best way to have your weed(s) identified is to take fresh samples or a clear photo of the weed to your local nursery and garden center.WeedAlert.com is a good website that has a massive listing of weeds you can search by name, appearance and region.
Methods of Weed Control in Groundcover Plantings
How you will control a weed depends on whether it's an annual, biennial, or perennial. Annual weeds complete their growth in a single season and have shallow roots. Annual weeds should be pulled or eradicated before they flower and make seeds. Perennial weeds are harder to remove since they may have large taproots, rhizomes, or runners that are hard to get rid of completely. The tiniest piece of root remaining after pulling a perennial weed can produce a new plant.
Weed Prevention in Groundcover Plantings
Weed prevention involves killing weed seeds before they sprout. There are several effective weed prevention products available on the market, which are available at most local nursery and garden centers. You want to avoid using weed preventer products, such as Preen & Green, which also contain fertilizer. The problem with these combination products is that they fertilize indiscriminately regardless of the nutritional needs of specific types of plants.
In my landscape and flower beds I use a granular weed preventer that contains Treflan. If you can't find it at your local nursery and garden center you can buy a landscape weed preventer online here. Treflan is a granular product you can spread with a hand-held or walk-behind rotary spreader. Keep in mind that weed preventers will not kill perennial grassy or broadleaf weeds that return from their roots or spread from runners. So, yes, this means its a good idea to keep the lawn edged on a regular basis during the warm season to prevent runners from spreading into your groundcover beds!
Postemergence Weed Control in Groundcover Plantings
The term "postemergence" refers to actually killing weeds after they have sprouted. Depending on the weed killer, and whether or not it is selective or broad spectrum, using these products can be a little tricky.
Broad Spectrum Weed Killers - These weed killers, such as glyphosate-based Killzall or Roundup, will kill just about any plant they are sprayed on - including your desirable plants if you're not careful! This can be difficult to do on windy days or if your groundcover plants are growing close together. Pulling weeds by hand is the safest way to eradicate them without harming your groundcover plants. If you do decide to spray a glyphosphate-based product make sure to adjust the nozzle on your sprayer so that it sprays a jet rather than a mist or fog, and don't pump the sprayer up too much. To avoid drift, spray on a calm day. When using chemicals, always follow mixing and application instructions on the product label.
Most local nursery and garden centers carry a brand of glyphostae weed killer. Or, you can buy a broad spectrum weed killer for us in landscape beds here.
"Over-The-Top" Grassy Weed Control in Groundcover Plantings
If you "forgot" to edge your Bermuda lawn for a few months, and your Bermuda grass lawn has sent runners into your groundcover planting of juniper, liriope, cotoneaster or other groundcover plants, never fear - there are "over-the-top" herbicide sprays that can be used to effectively kill weedy grasses without killing your desirable groundcover plants. That being said, always check the product label to make sure your type of groundcover plant is on the "safe list." Most local nursery and garden centers carry over-the-top weed killers. If you can't find one there, you can buy over-the-top selective weed killers online here. When using any chemical, always refer to product labels for mixing and application instructions.