I planted SAC in September. It did just fine. :)
Just keep them well watered. I would say no fertilizers either. Just the water for now. In spring you can begin fertilizing.
Make sure the hole is amended well with compost.

Would the type of clematis make a difference? I know SAC is suppose to be a vigorous grower and would size of the clematis matter, ie gallon vs small potted ones?

Julia

If you can get gallon then by all means plant that one. Otherwise, I don't really think it matters. I always planted right out in the garden without much trouble. The sooner you can get them in the ground the better too. They need time to grow roots to survive the winter.

The advantage of fall planting is that the soil is still warm, but the air is cooler, so it's a good time for growing roots and there's less water stress on a new plant. I often plant in the fall, even after frost, but usually before a hard freeze. We often have 6 to 10 weeks between the first hard freeze and when the ground freezes, and if we have early heavy snow, the ground doesn't always freeze. I do mulch areas with fall plantings particularly deeply so that the soil stays warmer longer and so plants don't heave if the roots haven't grown enough to hold to the soil well. We have good snow cover most years, so I don't worry over the winter about freeze thaw cycles, just in April for about 3 weeks. I haven't ever lost a fall-planted clematis in its first winter, though I do sometimes lose older plants over the winter due to the cursed voles.

Thanks for all the help. I feel better about letting them ship in September.

Julia