isn't mustard a small, yellow flowered annual growing to 2 or 3 feet. Please slap me if miss read your post or there's another mustard

Badfish the mustard seed in the Bible is a totally different plant (salvadora persica) and really does grow into a tree.This confused me for years! I only made the effort to look it up a few months ago when we were shown some seeds in a church service - and tryly they were the smallest seeds you can imagine!
I have no idea where you'd get the seeds as I think the person who showed them to us had brought them back from Israel, though can't see any reason why they couldn't be grown for a few years under glass. Perhaps they enjoy the same conditions as some cyclamen, which also come from those parts?

Thanks for that answer Stera. I've learnt something now, as I also didn't know about the biblical mustard tree.

Cheers Feverfew!