I'm planting my parking strip and thought heathers would be a good idea since they are, once established, low water use plants and also are evergreen.

My question: Heathers will be making up the bulk of my parking strip, but I have three sections where I have Betty Prior roses underplanted with geranium Rozanne. I'm wondering if the chemical the heather sends out to prevent other plants from growing near it will harm my roses. How far away from the roses does the heather need to be?

I do understand that the roses and heather have different water requirements but I didn't think that would be a problem since the strip will be watered by hand, and the roses will just get more water.