West Sussex,
United Kingdom 
Hardy arum lilies.
I have a lot of the tall white old fashioned arum lilies which I planted in pots about 3 years ago. it was supposed to be a temporary measure but the poor things are still there.They haven't flowered much but they look very healthy and have multiplied. The foliage is usually decimated by frosts but the plants pop up happily again in spring. When would it be best to split them up and plant them in the ground and do you have any tips to encourage them to flower more, please?
26 Nov, 2020
Answers
In a pot, they will also need regular feeding while the plant is growing, though maybe not for the first month or two after repotting. Tomato food is close to the perfect formula for them.
27 Nov, 2020
I don't think I have any space where I could keep them frost free but I will find a sheltered corner under bushes. Thank you for the link and the tips on feeding. I'll sort them out in spring and maybe have a good display next year!
27 Nov, 2020
I would keep them frost free over winter and then knock them out separate the corms/tubers and repot in early/mid spring. Any good moisture retentive garden soil should be fine. They do like some shade too.
https://www.rhs.org.uk/Plants/19190/Zantedeschia-aethiopica/Details
27 Nov, 2020