I cut them back to just above ground level in the spring. They grow very tall, 4 to 5 ft. and they flop in late summer. Staking is not attractive. Full sun. I have not able to confirm this on any website, although I believe that the growth can be controlled by cutting back in June without affecting the flowering. Any thoughts?
Thanks for contacting the Toronto Master Gardeners. Your question asks about pruning your Russian Sage (Perovskia atriplicifolia) in June to control the growth of it.
As recommended for this plant, you are aware that it should be cut back to just above the lowest set of leaves in the spring. An additional pruning in June would also help to keep the plant somewhat tidier and prevent it from flopping. Taking off the top one-third of the stems will encourage upright growth; make sure that you cut back to a flower or leaf bud on each stem–the stems will continue to grow from there. You shouldn’t need to cut them all–having various heights would provide a thicker plant overall. Furthermore, if the plant stops blooming later in the summer, new growth can be encouraged by removing the top portion of the stems.
As you are aware, Perovskia atriplicifolia needs full sun. In what type of soil is it planted? It prefers a dryer soil with good drainage. Once it is established, it is drought-tolerant. Nevertheless, if the soil is too rich, it will grow taller and tend to flop over.
Yes, staking can be unattractive; however, you might also consider planting other plants such as Coreopsis or Rudbeckia (black-eyed Susan) or even some ornamental grasses (Panicum virgatum–switch grass or (Eragrostis spectabile)–purple love grass. These plants would be able to support the Russian Sage branches and provide an attractive colour contrast.
We trust that these suggestions may be helpful to you.
Please refer to the following question for additional insights: Pruning Russian Sage