Limiting aphids on rose buds alternatives to ladybugs

Hi, a place I work grows approx 200m of roses. I was questioned by the owner on how limit aphid damage besides using ladybugs. Obviously no pesticides.

He has access to a wide range of essential oils, has anyone any experience with these as a deterrent.

The only other idea I had was using equisetum (horsetail) which is said to have a high silica content and may help strengthen cell walls against penetration

Any other natural remedies would be most greatful

I find soil PH and chemistry has more long-term effects on limiting aphids than topical treatments.  As our soil here is quite acidic, an application of wood ash before the spring rains stop helps tremendously.  If they come back in the summer, I'll put some borax (from the laundry aisle) on the soil as that's another trace mineral we are deficient in here.  Borax also limits the ants that can plant aphids on the plants.

It's very much about customizing the soil treatment to your local soil.  

My great-grandmother was famous for her roses.  But she was living in a time before we had detergents and she washed her dishes with a soap made from tallow and wood ash.  After she finished washing the dishes, she would pour the water over the roses (from the second-story window) and the oils from the cooking, as well as the soap, would prevent aphids from coming on the roses.