Posted: 02/07/2015 at 23:05
You will get better results if you get the manure down now and delay planting until next spring. Doing that will give the worms (and the frosts) time to do their work. If you have room you can still buy the perennials now and grow them on in pots (re-potting into larger ones if necessary) then plant them out next spring. Planting larger, well-grown plants tends to give better results than planting small ones as some may not survive their first winter in the soil. Larger specimens are usually considerably more expensive so that is also a good way of saving money.
Having said that I have sometimes been a bit impatient and have dug-in (very well rotted) manure and planted straight into it and most things survived.