John Innes No. 2 or 3, or someone makes a rather good multi purpose compost with added John Innes - used it recently, can't remember the make though, might have been Bowyers,, but it seemed surprisingly good, not full of rubbish like a lot of multi purpose are these days.

Thank you. jillyg

John Innes is too heavy and will compact within a season - I would not recommend it. I have grown literally hundreds of huge Buddleja in pots and use peat based multi-purpose compost (sometimes cut 30% with cheap peat-free compost), adding 10-15% perlite is the key and even a little sharp sand too.
Avoid coir at all costs - they hate it.
High potash feed occasionally too.

Well i'd disagree with that Buddlejager, These are Buddleias we are talking about....the plants that will grow in concrete. Peat based multipurpose compost has only been popular for the past 25 years, before that, it was all JI.

I worked at a huge municiple nursery and we mixed our own JI (7 sterilised loam, 3 peat, 2 grit) which was then shredded before fertilizer (John Innes base) and lime was added. Whether it was JI 1, 2 or 3 depended on the amount of fertilizer.

This was used for all nursery stock, tropical plants and bedding with no problems what so ever. The good thing about it was that we could add stuff to it such as shredded manure for hungry plants such as Fuchsias or other stuff such as charcoal or even vermiculite.

Conventional wisdom is to use John Innes for shrubs, yes.

But that doesn't mean it's always best. And the fact that feral Buddlejas grow in mortar and rubble doesn't equate to to growing proper cultivars in anything without consideration. They are actually very heavy feeders and the mistake people make isn't so much the substrate but by not feeding them often enough when in a pot.

As an aside, I grew hundreds of Buddleja seedlings in JL seed mix. I have been repotting stunted seedlings into the multipurpose/perlite mix and they are taking off. Honestly, they don't like JL as much as a more open base (like peat-based composts).

And why add vermiculite to compost? It crushes and provides no aeration or water holding benefits. Perlite is much better.