> I have two very large palms (Cordyline australis, the Cabbage Palm) at
> front and rear of my house. They are around 15 feet high and blocking
> light to my house and potentially causing subsidence.
Cordylines, unlike say oak trees, don't actually increase very much in
size simply because they get higher. Rather, the crown of the plant
mainly gets further away from the ground without getting very much
bigger - well it does get a bit bigger but nothing like on the same
scale as typical trees. Remembering that it is leaves rather than wood
that places the main demand on the metabolism in the roots, we realise
that the metabolic load the roots need to service for a Cordyline of a
given height in comparison to typical native tree is much, much smaller.
So they need much smaller root systems than those native trees. So
they aren't going to present any subsidence risk. True palms are
similar. I've planted a Chusan palm (Trachycarpus fortunei) - which
incidentally is rather more cold tolerant even than a Cordyline - right
next to my house and I'm not bothered.
You are actually quite lucky still to have a full-height Cordyline.
Most people had theirs involuntarily cut back to ground-level during
Cordylines do sometimes resprout from the trunk rather than from ground
level. I have seen damaged cordylines with large numbers of new shoots
at various levels up the trunks. Typically, though, many will abort,
unless you are fairly quick about rubbing out the ones you don't want
and encouraging the ones you do want. I think these new trunk shoots are
more likely to happen if you just remove the growing tip, rather than
make a major shortening of the trunk. So a possible strategy is to cut
out the growing tip, retaining plenty of leaves, and see if you get any
new shoots part way down the trunk. You could then rub out the shoots
you don't want, and later, once the favoured shoots are well
established, cut off the trunk off just above the shoots you wish to