I can't tell you much about darcyi because I seem to kill it and for me it never grew particularly big the first year. Van Remsen is another story - how does 7 or 8 feet sound and unable to stand on its own. You will need to ring it with stakes and wire. Last year I tried interplanting it with Mexican Sunflower and that kept them up for awhile. The best result was next to a trellis covered with Cardinal Climber vine. It grabbed a hold of the Van Remsen stems and kept it upright. One out of 4 plants wintered successfully in the garden - 4 for 6 the winter before. Once the last one passes I don't think I will grow it again. All that said it has a very beautiful flower, the biggest I have seen on a guaranitica. Don't expect flowers until August.

what zone are you in?

Salvia darcyi is very frost hardy once established, but younger plants may not survive a cold winter. But older plants grow to 4 ft tall with a 6 ft. spread after a couple of years, it does spread around! Stunning Salvia!

I cannot address you cold tolerance. If you don't want runners forming plant it w/Rock (underground as well).
We have Rocky limestone out croppings plants there do not
form runners. Plants in Garden soil will.I need to grow
Van Remsen have had no experiemce with that one.
Art

I don't grow 'Van Remsen' (it's on the wish list), but I do grow one of its parents (S. 'Brazil') and to prevent flopping, I cut it back by half in May/June of every year. Makes for a much sturdier, less floppy plant. I bet you could do the same with 'Van Remsen'.

I am on the 7a/6b border, temperatures rarely fall to subzero F. Friends grow Darcyi successfully in this zone. Brazil has never gotten top-heavy here nor has Blue Ensign or Argentina Skies. I guess I could try cutting VR back in June and see what that does.