The soil in the backyard (where the roses are planted), and just about everywhere else, is basically sand on top of the clay. Because of the woods in the back, there is a little top soil, but not much. I've done my best improving the area, but I'm still concerned the soil isn't good enough.

I was thinking that plants commonly grown as green manure (clovers, rye, buckwheat, etc...) could be sown in the places between the roses, and then cut down/mulched over.

Would this work, or would the would the roots of the green manure interfere with the roses?