I bought one of these 4 years ago, and it grew reasonably well until 18
months ago when a a few leaves started to die. This year 2 out of the
original 4 crowns appear to have rotted taking all the leaves with them.
The remaining 2 crowns appear healthy but just have 2 leaves per crown
although a new strong looking shoot has been growing this year without a
problem so far, but the plant now looks very sparse.

The plant has been growing in a 9" pot. I have never changed the soil
over the period, and wonder if this has anything to do with the ailing
Kentia. I cannot find anything on the web that suggests this is
necessary. I never over-water, using very limey tap water, and
occasionally feed with phostrogen.

Any ideas/sufggestion welcome.

The 'Kentia' (Howea forsteriana) is a solitary palm, but several
plants often are grown in a pot to provide a fuller effect. It is a
native of lowland forest and scrub on Lord Howe Island and needs
neutral to slightly acid conditions to really thrive. Watering with
hard tap water over several years is likely to cause an excessive
build-up of calcium deposits within the compost although this is more
likely to result in leaf yellowing rather than plant death. However,
the compost in which your plant is growing will be very stale, devoid
of essential nutrients by now and it is almost certain that the
structure will have broken down. Adding phostrogen under such
conditions will not replenish leached out nutrients, but it can lead
to a 'salt' build up in the compost and this will kill plant roots.

Your best course of action is to very carefully 'de-pot' the remaining
plants, gently rinsing off any remaining compost and trimming away
roots that are obviously dead. Pot up the 2 live plants in the
smallest container that can accommodate the roots using a mixture of
equal parts John Innes No2 and any good quality multi-purpose compost
to which you should add about 10% by volume of perlite, horticultural
grit or sand. John Innes is a loam-based mix which holds on to
essential elements for far longer than soil-less composts and the loam
acts as a buffer against salt-build up. It also retains its structure
for far longer than standard soil-less composts and is far better for
plants that are going to remain in the container for any length of
time. The perlite, grit or sand will ensure that the compost remains
open and well aerated, which is vital for healthy root growth.

Do not be tempted to provide too much root room. Howeas are naturally
slow growers and it will take a very long time for their roots to fill
a large pot and the compost will remain too wet for too long. The
compost will stagnate and any remaining roots will die. After
potting, give the plants a good soak, drain off and place in bright,
indirect light. Water only when the compost becomes slightly dry and
lightly mist the foliage daily to increase humidity around the plant.
You can commence feeding every 4 weeks once you are sure that the
palms are growing strongly, which could take up to 3 months or more.
Phostrogen is not the best choice for feeding these palms - a much
better option is a seaweed based fertiliser such as Maxicrop.