This pot will be fine Amsterdam. The restricted roots story is a myth - trust me!

Thanks Sheilabub.

Yep, totally agree with Sheilabub - they don't need restriction at the root.

They have been known to break pots with their roots!

Have ordered said pot and wanted to know when the best time is to dig them up and transplant them in to their new pot and what soil to use?

In my experience, they do best in a well aerated, fast draining mix. I couldn't speak to the time, though, since my climate is so different.

Well you could risk it now, but the end of August and September is probably better. Bear in mind that many varieties of Agapanthus are not entirely hardy, and in pots will be even more vulnerable to cold through the roots, so you may need to move them to a cold greenhouse or similar during the colder parts of winter. Multipurpose potting compost mixed with a little grit should be fine.

Thank you Bamboo. Will wait a little while and put under cover over the winter.

Bamboo - what type of soil should I plant them in-I read loam based soil is the best for agapanthus in pots? I would really like to increase the chances of them flowering as I know they can be temperamental. Would I be best to purchase some new bulbs as one in my border hasn't flowered but the other has. Will they adjust to their new home in the pot and could I be doing something like feeding now for the one that's coming to the end of flowering? Reading this back I realise I have asked you so many questions!

Don't feed now, its too late - feed when the foliage appears up to end of June, or just give a general purpose granular feed in April/May. I guess you could use John Innes No. 2, but it is heavy when wet, making the pots heavy to move around. Mine is just shoved in ordinary multi purpose compost, and it flowers every year, seems to thrive on neglect... as for binning the one that hasn't flowered, I wouldn't, I'd give it a chance to see if it prefers being in a pot...

Thanks Bamboo. I have just received the rather larger than I anticpated pot and hope to plant it up in Sept. Do their roots go deep down ?I ask this as the pot is huge and filling it all with compost will make it impossible to move! Might add some polystyrene in the bottom.... I have added photos of the new pot to the question- see if it works!

That sort of pot can be prone to blowing over in a strong wind - having polystyrene in the bottom might make that more likely. I'd put a couple of crocks in the bottom and use multi purpose, or that and a little John Innes mixed in.

Thank you.