Annual flower beds add a pop of ever-changing color to your home's landscape, but they can look unkempt if weedy grasses invade. The following steps can help you prevent grass issues in flower beds.
1. Apply a Full-Spectrum Grass Killer
A full-spectrum grass killer will kill all types of grass, from invading lawn grasses to tenacious crabgrass. "Full-spectrum" means that it will target both the leaf blades of actively growing grass, as well as the roots and any exposed seeds. Make the first application 4 to 6 weeks before planting the annual flowers, as it can take up to a week for the herbicide to complete its job and you need time for the rest of the steps.
2. Till and Wait
After about a week, fully till the bed in preparation for planting. This will bring up any remaining grass seeds or roots that escaped the first herbicide application, as well. After tilling, let the bed rest for about a week. During this time, weedy grasses may begin to sprout in the bed.
3. Make a Second Herbicide Application
Now it's time to do the second full-spectrum grass herbicide application so that you can destroy those grasses that survived the first application. Repeat the same procedure as the first time, tilling the entire bed about a week after application so that the herbicide has time to work.
4. Lay Down Mulch
There are two types of mulch to use in an annual flower bed. The first is plastic mulch. After you have fully prepared the soil, lay down a sheet of black plastic mulch to cover the area of the bed. Cut planting holes through the mulch for each plant you are putting in. After planting, cover the plastic mulch with a 2-inch layer of attractive mulch, like wood chips. Plastic suppresses most grasses from spreading into the bed while also preventing seeds from blowing in.
5. Install Edging
The last step is to edge the bed. Lawn grasses often get into neighboring flower beds by sending out rhizomatous roots. Mulch helps slow this, but may not prevent it completely. Installing landscape stripping that extends several inches into the soil can prevent the grass from spreading, though.
Once the majority of the grass problem is handled, you may only need to perform a single non-selective systemic grass killer treatment each year right before planting. If any grass does pop up throughout the growing season, apply the grass killer with a targeted sprayer.
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