Will Russian sage grow if planted with pachysandra and vinca?
Russian sage likes sun, more sun than pachysandra and vinca. If in enough sun for good bloom on the russian sage, you may have sun burn, browning of the edges, on pachy leaves. In time, vinca will climb the russian sage which will affect that plants photosynthesis unless you prune it away. All three are well known for enlarging and not staying put. Vinca, in particular, is hard to get rid of once it is established
What evergreen should be planted in a small space with Russian Sage? The space gets full afternoon sun. There is an Oak leaf hydrangea in the space, that I would like to remove.
Evergreens make lovely additions to the garden and companion plants to perennials.
You should consider the soil type, sunlight, and the space that you have available for the planting.
Visit local garden centers to see the type of plants available in your area.
Even driving around the neighborhood to see what is growing and what might appeal to you is a great idea.
Here are some links to help you make a planting decision.
https://www.gardeningknowhow.com/ornamental/trees/tgen/evergreen-tree-varieties.htm
https://www.gardeningknowhow.com/ornamental/shrubs/shgen/evergreen-shrubs-for-privacy.htm
https://www.gardeningknowhow.com/special/shade/evergreens-for-shade.htm
https://www.gardeningknowhow.com/edible/herbs/hgen/growing-evergreen-herbs.htm
https://www.gardeningknowhow.com/ornamental/trees/arborvitae/growing-arborvitae-trees.htm
https://www.gardeningknowhow.com/ornamental/shrubs/boxwood/boxwood-care.htm
Should I cut this back after the summer? How far?
Russian sage should be cut back just before leafing out next spring. You will be able to see buds starting to swell. Cut back to 6 inches, making sure there are several live buds left on the stem. Large, budless stems should be cut to the ground. Since it can get tall and a bit floppy, some recommend cutting again to 6 inches when the plant is 12 inches tall. The trimmings are good deer/rabbit repellant. I place them over emerging tulips.
When is the best time to transplant Russian sage plants?
It seems like the best time to plant is in spring, however this hardy perennial can safely be planted now if you needed to. Here is an article on their care: https://wimastergardener.org/article/russian-sage-perovskia-atriplicifolia/
Received some russian sage. Can I plant it now(late fall)?
I would wait until early spring, if possible. If you plant them now, they may live, but they may also not have enough time to get established before any cold weather hits. Here is an article that will help: https://www.gardeningknowhow.com/ornamental/flowers/russian-sage-flowers/russian-sage-care.htm
You are asking because you know it is an iffy situation. December is fine for planting spring bulbs but awfully late to allow a transplant the time it needs to get roots established. Even in winter, the roots must take up water or dry out and die. Two suggestions: cut it down to 6-12 inches now and water the ground when it gets dry, even in winter.
In the New River area, how often should you water Russian blue sage and when should you prune them back? It is now the beginning of January and the blooms on most are done. Also should Mexican bird or paradise be pruned back now and to how far above ground?
Pruning can take place after the flowers have faded.
Watering is minimal with established plants. If your plants are new, they will need regular irrigation.
https://www.gardeningknowhow.com/ornamental/flowers/russian-sage-flowers/russian-sage-care.htm
Pruning your Mexican Bird of Paradise can take place after blooming, generally during winter.
https://www.gardeningknowhow.com/ornamental/flowers/bop/mexican-red-bird-of-paradise.htm