In a lot of gardening books it is often mentioned that onions or most members of the Allium genus (onions, garlic, leeks, shallots, chives, etc.) are good companion plants for roses. They are known to protect the roses from pests by confusing them with their strong scent.
I have 10 hybrid tea roses growing on the sunny side of my house. Last year they were hit by some aphids and roses eaten by aphids are heart breaking. This year I decided to take some action defending them. The hired guns I am putting on guard are the left over onions and garlic from this seasons vegetable garden.