Out out d... (allelopathic) couch grass

All the excitements of Chelsea Flower Show and our own Open Day now over, it's back to earth. All allotmenteers battle with our old enemy, couch grass, but only recently did I learn that it had negative allelopathic qualities and can actively inhibit other plants from growing. Having just digested that bit of information, I hear on Gardeners Question Time that climbing beans don't have a hope if they are beside onions and heaven forfend that we should sow radishes near our red peppers. On the other hand, I believe growing mint near your roses helps keep aphids away so I thought I'd take it a step further and spray my rose with mint tea!