As Franz says, lots of interesting info in this BL. I am very interested in the comments about crocus corms. As you might expect I get to see quite a few of them at this time of year. I have experienced all the phenomena that Ian shows. I am of much the same opinion on most counts. However I would not be happy planting my corms so close to the bottom of the pot. I want them to have a bit of compost under them to feed the new corms for next year. Do your roots grow upwards Ian?
The downward migration of corms occurs mostly in the species from habitats with severe summer drought, I have seen corms with a similar 'string of old tunics' myself. Perhaps this is more a natural feature of these plants than a 'need'. I think they will grow just as well if planted at a conventional depth.
The idea that virus may be responsible for the poor condition of some corms has occurred to me also. I don't think it is the only factor that can cause the problem. What taxa is the picture of? I have had a problem with virus in C serotinus which has had similar effect, this species seems especially prone and I have discarded all the suspect material this year.
Watering issues are varied. Does insufficient/erratic watering at the start of the growing season result in less extensive rooting? If so this would have a serious negative impact on the development of a strong and healthy corm for the next season. This spring temperatures rocketed very early with pots drying out quickly, failure to keep up the watering at the end of the season can result in premature dormancy although the high temperatures alone can be a sufficient trigger. Premature dormancy will seriously effect the size of new corms and the amount of resorbtion of the old corm. This has been a significant problem here this year but not as serious as I feared at the time.
