Hi , there , Scottish , hope you spent a good Christmas .
It all seems a bit of a storm in a teacup at this distance , but the pressure is on from all angles at the time ; just waiting to get New Year's day here and then we can really get on and make with the seed catalogues !
John Innes , I know not , but stand-by , someone will .
Happy New Year .

Your JI will be OK as a base, Scottish, but nowadays it all seems to be made of poor quality loam and will be very silty. I would suggest a mix of one part JI, one part multipurpose (to add humus) and one part grit (for drainage). The grit will dilute the nutrien value of the JI but the multi-purpose should replace this.

Hi - hope you are well Driad! Quiet Christmas and will be a quiet New Year for us. I hope your New Year goes well and all the best when it comes xx

Bulba - thanks again for your help - should I add some bonemeal when planting up?

I've had a wee bit of an idea this afternoon, so to save me asking when I get round to it - what mix would you recommend for Sempervivums?

For all our potted plants we make our own compost from a basic mix of one part each: loam(soil)/leaf mould/grit. If we are potting high alpines we would add more loam and grit; if woodland plants we would add more leaf mould. Our materials have little in the way of natural nutriens so we also add some bone meal.
My suggestion to you, Scottish, was to use JI and multi-purpose compost so you should not need to add extra nutrient in the form of bonemeal to this. OK?
For your semps I would say use similar to what I suggested earlier but with only half a part of multipurpose. As they grow in a thinner and leaner soil on the mountain they do not need as much nutrient or humus.
Sempervivums are sometimes called 'Roof Leaks' and are indeed grown on the roof of houses - they get little of anything here and survive on neglect. (In Scotland I would suggest that our roofs get rather too much rain to make them a suitable position for growing semps).

Got that B.....thanks ever so much. Especially for the tip re the difference between the alpines and the woodlanders. This will help me enormously. There is so much info out there on the web - it's better to ask rather than trying to pick up from various websites.

The rain up here only causes the unwanted 'roof leaks' :))

Which Saxifrages are you intending growing?

The 3 I've chosen are Southside Seedling, Monarch and Hime Owdboggy. They are hold up in a cold frame at the moment.

The first two I grow, but do not know Hime. Go with Bulbaholic's suggestions, but I add a little lime to composts for Silver saxifrages like those, not much, say a dessert spoonful per 5 litre mix.

Looked up Hime, it is a stolonifera type. Do not grow those at all, but I have a feeling they like a different set of conditions to the silvers.

I agree with the addition of a touch of lime for the silvers, I use a similar quantity to Owdboggy.
The stoloniferous types are of Asiatic origin and we grow these in the garden in a more humusy soil. They tend to spread out more than the silvers and I find that they soon get too large for a pot.

Beat me to it. Never had any success with the stolonifera types.

Thanks again both of you, most helpful advice . I bought another 'silver' today (Aizoon minor) to grow with the other 2 and will find another home for Hime in a border somewhere.