When does yours usually flower, April, May or June? (It varies round the country)

What soil type have you got there is it acid? If so this will need to be considered when planting, I thought you might consider Fothergilla or perhaps a Gardenia if it is acidic?

put a white flower like blue bells or white geraniums, white goes well with purple and makes it look nice. but if you do have a tall growing ponticum then its best to get a star of Bethlehem flower climbing around it(can be bought in white)

Would a white clematis montana work?

I like Pamg's idea as the plant/shrub needs to have some height to grow through the R. ponticum. Snag is it could take a strangle hold on the Rhodo and actually kill it off. Not sure Ornithogalum would work as, to my knowledge, there is no climbing version. Maybe a light coloured honeysuckle?
Do you want something climbing through or in front of Stera? If simply in front of then a white Rhodo that flowers at a similar time could work well.

Or how about a camellia in white or pale pink.

All lovely suggestions, and all desirable stuff, thank you! I was thinking of something fairly low growing, say about a couple of feet max to go in front rather than climbing through, though I had toyed with a clem for later in the season. Hadn't thought of it strangling the shrub though and I agree, montana would be too strong. I thought any shrub taller than a couple of feet would make the rhodo go bare at the bottom, which wouldn't be nice in winter.The ornithogalum is a nice idea but would have to be in addition rather than instead.
I can't honestly remember the exact flowering time Bamboo, which admittedly makes answering the question challenging to say the least! All I can say is that we are in the mild but wet and windy south west, and it flowers early rather than late.
Drc, pH 6.5.
I did have some geraniums there WLB but they were pink too and made it worse - also they were very thuggish. Is there a white one that flowers early? I only have the Kashmir White that's a bit too fragile looking and doesn't start early enough.
Looks as if it might be best to wait until it does flower and then look round and see what else might be around. I am toying with a manteau d'Hermine for part of that bed but it's not early enough for that spot. Wonder how white Dicentra spectabilis would do there in dry ground and full sun - not the best situation?

Yellow flowers go so well next to purple, so a good choice would be the yellow tree peony, which to be honest is more like a large shrub, but we have to note that whilst the rhodi is longer flowering the tree peony will at most be in flower for about two/three weeks, but if they flower together then the effect is fantastic, but we have to look beyond the flowering period, the tree peony will give you fantastic architectural foliage throughout the summer in autumn you have long bright red leaf stalks and large seed pods that open and turn black for the winter and tend to stay on the plant and they look rather ghostly hanging on the stems, also large buds which turn red as they swell in the spring, worth a shout is this plant, but patience is needed for it to get going, after about two years it will reward you, both the leaves and the dormant structure will look great with the rhodi as the backdrop.

Just to add having seen your post, tree peony once established can be cut hard back, as can your rhodi if you need to reduce the size, if so then do after flowering, late flowering clematis you make like clematis tangutica, flowers are like yellow lanterns.

Would have to say we gave up on our yellow tree peony as the flowers were so insignificant as compared to the blood red one... frankly we had to hunt for them and the damned thing always looked leggy no matter what we did... Couple of foot Stera - perhaps some of the late flowering white daffies?

That's a very interesting suggestion Julien, I didn't know they could be cut hard back. Will investigate. Tangutica would be much to big and vigorous for that spot though. I used to have it in the back garden three houses back. (All these house moves are dreadful for gardeners but duty says follow OH...)
I had wondered about lemon but eveyone else thought of white. Just looked at Kelway's site - expensive aren't they? Need to be sure before splashing out!

Personally I'd stick with white rather than lemon... colour of the lemon shrub slightly off and you have a ewe moment. Mind you our garden i not planned in that way at all, no colour theme, simply lots of different alpines. Oh, and the whole garden is suffering neglect as we re out birding so much the basics aren't even getting done :( Reality I though that I can birds watch and walk around on the level, can't dig or weeds...)

white geraniums do flower early since my one which is white with a pink center is flowering right now!
I think yellow would look nice but then the purple would stick out more, go with white or pale pinks.

I suppose something like Euonymus emerald gaietys out?
its just so bright and cheerful on dark winter days well all year round really, then something growing through the ponticum?

I'd choose a Spiraea I think, an early flowering one, which, with luck, will be in flower at the same time, so have a look at S. x cinerea (previously S. argutea compacta), or S. nipponica 'Snowmound'. Even better would be S.x vanhouttei 'Pink Ice', but it might flower a bit too early - although the leaves would still be a great contrast and maybe tone down all that lilac... and its slow growing so won't get too large too quickly.

You say your bush does not seed around. I dk how long you have lived in your house but maybe reading what is said on this site could make you change your mind. http://www.eryri-npa.gov.uk/the-environment/invasive-species/rhododendron. I'm sure you could get a reasonably fast growing alternative because it is such a dense grower and feeder that very little will survive alongside it.

Scotsgran:
Thank you for the warning. But we have been here 8 years and there have been no seedlings and no suckers. I do know the trouble they cause in woodland where they get a hold and was a bit apprehensive when we came but the bush must be about 20 years old by now and no sign of spreading.Rhododendron seeds germinate best on bare ground and have difficulty where vegetation there is already dense, which explains why they take hold mainly in dense woodland where ground plants are sparser.

So because it is large and a good shape I will leave well alone for now. It is on a very steep and shaded wild bank where nothing much except ferns coarse grass and a few brambles grows anyway when the daffodils have finished.
(see my pic no 13, though you can't see the rhodo on it)

Bamboo, I did have a look at some spirea pics yesterday and thought perhaps they might do, but have only ever grown one small pink one so had no idea which one to go for that wouldn't get to big or would stand cutting back. I'll have a look at those you mention.

MG I like the idea of white daffs too, if I can find a late variety. I think there are some on the wild bank I might move.

Pam, I do agree and there is already a Silver Queen just along from where the space is. I love them!

WLB what variety is your geranium? No many flower this early - or is it still on the go from last year?

Yellow - yes, it would need to be pale and if it turned out deeper it miught look awful.

MG - My garden isn't planned either, it just happens (or not!) When there has been a plan eg a blue and lemon bed, I've been too soft hearted to hoik out things that didn't match, so gave up kidding myself that I could ever design anything.

Well it certainly won't be Goy's fault if something good doesn't happen in that cornerr soon! Thanks everyone.

Scotsgran we have what we 'think' is a R. pontica lurking in a corner of our garden. Was there when we moved in 25 years ago and whilst it has increased in height has not seeded anywhere and is a damned good corner blocker for us :)

Is the answer in the "think"?.

Well if it isn't I don't know what it is... I suspect that the beastie behaves differently depending on the soil it is in. That particular corner is basically dry and we have never done anything to the soil. A Kilmarnoch willow growing next to the Rhodo is also smaller than I would expect after these many years.

That makes sense. Stera has said her one grows in a dry area.

it is a cutting that I got from another pot and its now started to flower! don't know what variety though

MG - My garden isn't planned either, it just happens (or not!) When there has been a plan eg a blue and lemon bed, I've been too soft hearted to hoik out things that didn't match, so gave up kidding myself that I could ever design anything.

Yeah for unplanned gardens... When we were creating all the raised beds, one at a time, Bulba simply got on and made them no idea how the shape or size would work until they were done. Hence there i not one straight path in our garden aside from the one along the rear of the house and even that isn't really straight!

Who wants straight paths anyway? I always have mixed feelings when people talk about their OHs doing the digging and bed construction. I do my own and am getting a bit past it! (Explains why there is more grass and fewer beds than in an ideal world.

Geranium: Thanks anyway WLB!

Julien - Kelways website has some real beauties. I read they prefer shade and my site is sunny and dry. so although I would love one ( or two...) it will have to wait until I get round to making another bed in the half shade.

Bamboo I think Spirea is going to fill the bill. Couldn't find either a picture of a supplier for the last one you mentioned though.

If you do go for daffodils I can recommend 'Ice King'. It grows to around 18" and flowers in April. It is a carnation type double and is a relative of 'Ice Follies'. It is single and grows to a similar height. I have had it in the garden for years and it has never let us down. Both are white.

Thank you Scotsgran. Have had a look at these - very nice. Pity its too late this year but I have made a note for next.

Stera I used to seriously help but with the Osteoarthritis in my spine I basically can't now.

Hmm, dunno what you've been typing into Google then, Stera, Plantify.co.uk appears to have 25 in stock with a lovely photograph to boot, though at this time of year, they'll look like a bunch of dead sticks.

Google Spiraea Pink Ice...

I typed spirea x van houttei pink ice as far as i can remember. Will have another try leaving out the first bit. Thank you.

Stera, I find if I left click on Spiraea Pink Ice where Bamboo has written it, then right click, I get a drop down menu. From that menu click on 'search with Google' and plenty of info pops up including nice photos of the plant. I find it less frustrating to do that than try and copy web addresses.

I found it eventually Scotsgran. But your info is useful - I didn't know you could do that - saves a lot of time! Thanks.

You are welcome Stera. I do not remember when or where I found out about it but as you say it is a real time saver.

MG I was so sorry to hear that - must be very frustrating, but what a good thing your OH is into gardens too.

I remember Spirea pink ice now,
pink and white flowes on the same plant, even on the same floret, its lovely and with a simple trim after flowering stays neat

Not quite, Pam - the leaves are completely freckled with white when mature, but when they first appear, are heavily pink tinged and pale greeny yellow - the flowers are all white.