I have a bed of Improved Golden Sedum that is healthy in every way, but wants to go back to lawn. This is difficult to weed, because the grass has a very dense shallow root system, while the Sedum has soft thin roots. Pulling the grass would take out a large part of the Sedum, and leave holes in the ground. How can I successfully remove this grass while maintaining the Sedum's health?
Here is a picture of how it looks after weeding. It is normally dense and tall.
Mulch helps a lot in this kind of situation. I'm thinking of ordinary pine/cedar/hemlock bark mulch. Before mulching, cut the grass as low as you can, or pull the tops off if it's too intermingled in the sedum to cut. When the grass grows through the mulch the roots are a lot shallower, and there's less of it. Because the roots are shallower, and because the soil underneath is moister, pulling grass without harming the plants around it becomes a lot easier. But resign yourself to losing some of the sedum when you do weed it. It will grow back!
Put on a pair of thin vinyl or latex gloves. Wet your fingers with gloves on in a small bucket of Roundup weed killer. Gently wipe your fingertips over the grass blades. Of course try to avoid touching the sedum. It won't require much, just wet the grass blades and the Roundup will kill the grass and leave the sedum alone.
I maintain a sedum green roof and I use Fusilade II to kill grassy weeds such as crabgrass and annual bluegrass and any ornamental grasses that blow into the sedum. I use .75 oz per gallon along with 1/2 oz of non ionic surfacent per gallon of water. It takes about two weeks to see results.
