"Lord0" wrote in message

I *think* it's a Bearded Iris - it certainly looked like one the last
time it flowered. The flower was purple with a yellow and black
speckled centre.

Tall Bearded Iris only flower once and after they flower they will then put
their energy into producing new rhizomes so if it is an old congested clump,
you will need to divide and replant the newer, younger rhizomes.

I was reading on the web that maybe it's planted too deep. This could
be the case as the border gets a lot of mulch and compost so the Iris
is in effect getting deeper and deeper each year. Sound plausible?

Yep.They prefer medium to heavy loam and slightly alkaline soil. They are
supposedly gross feeders but I don't bother to feed mine much (or in fact
water them much either) and they still flower so they are very forgiving
plants. I use them as 'pioneer plants' in areas on the outlying parts of my
garden.

I'm in Australia and have soil that in some places is still totally
unimproved from when the land was first cleared of bush. My soil is
relatively infertile in comparison to yours I suspect.

I don't mulch my irises so if mine survive in weeks of high 30+C temps, no
rain and most often no water as I use that on things that need it to
survive, you won't need mulch in the UK. In fact mulch could introduce too
much moisture round the rhizome which could rot them.