Last year I took several cuttings from a Penstemon. They rooted successfully and over-wintered well in the greenhouse, together with the parent plant. During the warm spell in early March I brought them all out and put them in a sheltered spot to harden off. The result is there's a bit of die back on the parent plant and its stems look healthy, but the leaves on all the cuttings turned brown and the stems look to be dying back. They all have a good root system, though. Have I lost them?