Bob,
It's 'as you were' with regard to your Dietes. I was misled by the
first, somewhat mis-shaped, short-lived flowers. This year it has
produced longer lived flowers with the correct colouration and
markings for D. grandiflora. Sorry about that :-| In my defence,
they are very similar :-)

D. robinsoniana was successful growing as several large clumps in the
cliff gardens down on the sea front up until the early '80s. I'd read
about it in the RHS mag 'The Journal' and was delighted to see it in
full flower here when I first moved down. Typical of council-run
'gardens', the clumps disappeared over the next few year and replaced
by gaudy annuals!!! I'm confident that it will grow outside here
provided we see some return to our more normal winters in the next few
years. Hopefully, increased solar activity will help shift or at
least ameliorate the effects of the Arctic dipole anomaly that has
caused us so much grief recently.

Jeff,
Derry Watkins does not answer e-mails and after several attempts I
gave up. I've tried seeds before, but as mentioned earlier it would
appear they need to be spanking fresh for them to germinate. To the
uninitiated, Dietes may seem similar to Moraea, but this one is very
distinctive when you see it face on. The flowers are a good 12cms
across or more held in successively opening clusters on 1.2m high (or
more) stems and have a rather powerfully sweet fragrance. It's a bold
evergreen with meter long, 5cms wide leaves and is pretty impressive
as a foliage plant quite unlike any of the Moraeas.