Cracked it!
I would love to say that the title of this post was an exclamation of pure joy as I achieved some solution to a problem that had been tormenting me for years. But no, it is the bad behaviour of my zantedeschia.
This is my second year with ‘White Giant’ and the original plant was split in three in spring and each section potted. Next spring I will plant at least one clump out to see how it does with a bigger root run and colder winters (it should be OK). The mild autumn has suited the plants well and after a summer of growth they are all flowering again. It was a job keeping them moist in the dry summer, but they are all the better now for some TLC.
Perhaps the biggest clump is in the pot it shares with a canna and Begonia luxurians, that I have shown before. Every day I think I must remove the plants from the pot, but the production of new flowers has put me off hacking the plant to bits to get it out. And I was worried that I would not be able to remove the plants without damaging the fibreglass pot. Well, I don’t need to worry any more.
The plant has increased so much that it has completely split the pot down one corner. I don’t think the pot will be much use once the plants are extracted but I will see if I can do something ‘creative’ with it.
The plants out the front are in ceramic pots but I lined them with bubble plastic so I hope that will have absorbed some of the expansion in the roots. But getting them out is now urgent, not just because the tulips need planting but because I don’t want more broken pots.
The Biking Gardener 
It’s a fine plant and should do well in the ground. Pity about the pot!
Looking very good. I didn’t realise they were hardy. Do they need full sun or would semi shade suit? I hope you can repair that very large pot.
The white zantedeschias are hardy. There are some with a pink flush that are hardy too, but not the coloured ones – though they may make it through winter in sheltered places. THis is the only one with spotted leaves that I am aware is hardy, though most people think the white spots are disease! At least in my garden. BTW the diascia cuttings rooted well and I have ten plants – thank you.