
Autumn is the best time to plant as the plants roots get established before the hot weather comes so the need for watering in the summer is grately reduced.
you can plant even when it is frosty, as long as the gound isnt frozen past the top few milimeters, and the plants havnt been kept sheltered.
We get bare rooted trees in december and have been known to plant in the frosts!!!!!
We do try to leave planting untill this time of year.
So GO FOR IT :D
SOmething I will say, Dwarf conifers do not stay dwarf. You really do need to keep them trimmed.
TYhe amount of gardens where we go and the customer says they were bought as dwarf 10 years ago as we are looking at a 15' tree!!!!!!!
So keep that in mind!!!!!
And Buxus common name Box, needs trimming several times a year to keep them looking the same as when you bought them.
Oh and cordelines, IF there is a really bad winter, the type we havnt seen in this country for about 15 years, it can kill the cordelines.
Sorry you may already know all of this ;)
Cant say wether it will look ok though as dont know what your garden looks like, but cordelines and slate look good together (Done that a few times in gardens) and as long as they are not all packed together it should look fin :D
Have fun :)
Lea :)