cattleyas, dividing up big plants

[headbanger333]

Greetings from New Zealand! have tried splitting up two quite large cattleyas. I have cut the rhizome in two places, giving me my lead group of 3 pseudobulbs and two other groups of 3 bulbs. I have tried this before with no success. I pot up the lead group, putting the other two groups in a moist sphag bag. After 6 weeks, they are extremely wizened with no sign of any root growth whatsoever. Is there something else that I am not aware of that I should have put in the bag, or is regrowth just a matter of luck? Has anyone had much success with divided cattleyas becoming vibrant new growths? Thanks in advance.