The message
from Paul contains these words:

A few days ago I planted a Sorbus Joseph Rock - about 8' tall, with a 1"
thick trunk. I attempted to follow the planting instructions to the
letter, but unfortunately managed to break the stake whilst hammering it
into the ground (heavy clay). So I just went ahead and planted it un-
staked.
(snip)

I would be particularly interested to hear from anyone (if there is
anyone!) who has planted trees unstaked, so I could benefit from their
experience.

Yes, it is quite possible and I have done it often, on a very windy
exposed site. (Although those trees were planted out much shorter than
your rowan and were on their own roots, not grafted). I much prefer no
staking or low staking, because some natural movement of the trunk
stimulates strong development. What's essential, is to make sure the
roots are not loosened; that a graft doesn't split under stress, and
that the trunk doesn't waggle a loose hole in the earth around it (where
water could collect and rot it). For an ungrafted tree a couple of heavy
stones above the roots, to steady it, will do the job. They only need to
be there for a year or two.

If your tree is grafted (look for a thickened "join" or scar slightly
above ground level) then you should protect the union by giving the tree
a low diagonal stake, fixed with a proper adjustable tree tie, about one
foot above ground level. You can buy such ties singly in good garden
centres. Adjust the fit at the end of each summer and remove it after
about two years.

Janet.