How can I keep grass from growing up through my false boxwood hedge?

No matter how much I edge around my germander, I still get grass growing up through it and taking over.How can I keep grass from growing up through my false boxwood hedge?
That is because germander has many, many stems, producing areas of contact with the soil that airborn grass seeds can plant themselves in between. If it is really driving you crazy, you can remove it and add a one-stem hedge, such as boxwood, yew, azalea, rhododendron or even oak leaf hydrangea, that you can mulch around. The only other alternative is to pulverize some mulch and drop it down in and around your germander. It won's completely eradicate the grass problem but it will reduce it and also make the grass that does get through easier to pull out.