I have to agree with Pam and Bob Flowerdew. When the roots have gone into my compost heat, which was on the dry side admitibly, they took hold.
For all my perennial roots I stick in a large tub of water. It does make for a smelly bucket - but can use the liquid as liquid feed - once diluted and come the autumn when it is all rotten the sluge gets put on the soil.

Regards
Cliff
Bawtry, Doncaster, South Yorkshire