Just in the prep room. the window ledge is right above the radiator so should have been warm enough. I've done it before in exactly the same way and its worked fine, just not this year for some reason!Did you grow them at 20 degrees? Only saying that because i grow them in my incubator at cold times of the year. I also sometimes buy a bulb a long time ahead and wait for it to start sending up the green shoot while in the fridge. I find that then it is ready to root.
other than that i buy loads of bulbs and set them all going in the vain hope i will get enough roots. Such a pain though!