Companion plants are grown for various reasons – they can provide year-round interest in their own right, flower at the same time as the roses, or fill in-between rose flushes. These plants need to be well behaved, have a non-invasive root system, and not ‘flop’ on their neighbours.
Sage, lavender, scented geranium, santolina, catmint and lamb’s ear that are grown for their foliage rather than their flowers and make good companions.
Tall growing plants with a see-through effect: cosmos, campanula, gypsophila, gaura and fennel can also be grown among roses.
There are several companion plants that can be planted in between roses – in general one would like a plant with a not too deep root system that will absorb the fertiliser and water that is meant for the roses.
Ground covers are good companion plants, such as alyssum, ajuga, campunula, Diascia, mazus, strawberry and Verbena.
With larger shrubs one would like to avoid a plant that is going to create shade on the rose – either plant them a good distance away or choose plants that grow upright rather than sideways; Phormiums, Acorus, Hebe, Cordylines, Coprosma, Kniphofia and Trachelospermum are good examples. Delphiniums look exceptionally good with roses.
Herbs like Rosemary and lavender can also be used and will aid in deterring insect from your roses yet these should be kept a 1.5m away.
Off course, roses can be used to under-plant larger roses.