Their the ones that look a bit like holly?
I think that you are right about them being acid loving, when you say not doing well maybe an iron tonic and an ericaceous mulch may help?

I have one in an acidic pocket and one in a neutral pocket, but as any rain leaches down towards the neutral I think this helps to keep bothe healthy. So as Pamg says an ericaceous feed might hep, You could do an emergency water with 1/2 pint vinegar to 5 gallon watering can. And you could mulch round it with bracken or any moss off your roof in autumn but still give it an ericy feed.

Could you explain a bit more about the use of vinegar 2ndhand?

I'd like to know where it said they like acidic soil - its not true. Osmanthus aren't particularly fussy about soil, and will grow well on chalky soils, which will be alkaline, so whatever's causing the problem with your Osmanthus, it won't be the ph. They like fertile, reasonably well drained soil in sun or part sun.
What symptoms does it have? Any chance of a photograph?

Its just that in some gc's its labelled as needing an acidic soil Bamboo so I,ve always discounted it but I trust your judgement

I was beginning to think mine had the wrong conditions,on reading this...but glad to see it is ok in fertile soil..Had no problem at all,from a small gifted one last year...and looking very healthy,with lots of new growth..same conditions as Bamboo suggested..

I confirm what Bamboo says, I have two Osmanthus, the variegated ones, and both have been growing quite happily in alkaline soil for the past 5 years.

Us too, soil with a good mix of lime mortar in it is defo alkaline.

Mine were planted in ordinary garden soil and are doing well enough to get too big for there location.

Pamg - is it really labelled like that in garden centres?! I'm shocked, its absolute twaddle...maybe they just want to sell more ericaceous compost, lol. My info's from the RHS and the Reader's Digest Encylopaedias of British Plants... and its growing perfectly well in our gardens here (neutral soil)

Maybe its me Bamboo.....probably the usual 'senior moment'... :0)

I still have a label for one of mine, it doesn't say acidic, but it does have diagrams for everything and the Ph with a hat is definitely on there. but sommat is ringing a bell that I found it wasn't that way inclined at all, thats why I planted one in a neutral area.

Many thanks to all of you lovely GOYers who answered my question. I actually found the reference to acidic soil on a Google site but can't remember which one.

I think that if it's not the lack of ericaceous soil then it's probably lack of food as the border it's in has large trees a short distance away. I'll try giving it some feed which I haven't done so far and see if that makes a difference.

It looks OK but is just not growing much. Thanks anyway for your help everyone.

Better not to feed it now at this end of the year - give it a feed next Spring, as growth begins. It may need extra water though, if its near large trees, that can be a very dry spot indeed. I know that sounds daft with all the rain we've had this year, but your plant's only been in a year and won't yet have an extensive root system. Another year or so and it'll take care of itself, even in dry spells.