I'm no expert but my experience growing one tree fern over the course of ten years is to treat it like a normal plant and not some kind of freak. They do grow roots and you should keep the ground moist, not just water the crown. Why would you not want to dig up the roots with the plant? it would be sure to grow better once replanted. Obviously you can cut off the fronds before you move it.

"I think I read somewhere once that you can literally cut the bottom of the trunk at ground level and it will just grow roots when eventually replanted is this correct?"

Yes. That's how they're sold here in Tassie and how they're shipped to the UK. The usual recommendation down here is to saw it off - they re-establish very easily.

Whether you want to do this or not will depend upon how long it's been in the ground (they develop a fairly weighty root system) and whether you want to preserve the stem height (they're slow growing, and you'll need to drop about a quarter of the stump length into the ground to make it stable). Whether you saw it off or not it would be a good idea to remove the fronds when you transplant - less stress on the plant and easier transport.

As for soil, they're not terribly fussy. Anything slightly on the acid side that's moist but well-draining will do.

Good Luck

Kayman

Commercially harvested tree ferns are chopped off at ground level for convenience and with the expectation that a prportion will be lost. For your only plant I would suggest getting as much root as practical. Some is better than none and there's certainly no point cutting off part of the trunk unless you have to.

Compost? Is it in a pot? If it is then you have no reason at all to chop it. If not then you don't need compost, plant it in your soil unless it is very alkaline (chalk or limestone).

If you have the muscle-power available - treat it like a Camellia* for transplanting - and be careful with the young frond buds. Some trunk protection (shade and dampish) would probably be appreciated if you take back its frond cover. *At least a foot out from the trunk all round and a good saucer-scoop underneath, slithered onto a tarp and then baled to hold it as intact as possible.

It's probably a madness of my own - but I'd actually put a tag on the plant to indicate which way was facing south in your present garden - and I'd plant it in the same position/direction in the new place, as far as possible. It seems to help the plant settle in quicker. Plant it at the same depth as it came from. Ensure good drainage. They're not big on swamp-living.

If you have to stake and tie - wide strapping rather than anything thin. Serious wind shelter until it is re-established, and a snow, or frost hat, if possible/needed.

A mulch of well-rotted leaf litter, nothing too papery or felted-together. Something that lets the air and rain through. Even small rounded pebbles that don't bind, or bark chips.