I think you might be thinking of Rootgrow, which is mycorrhizal fungi, available on line. You don't have to do it though, its not essential, and at £10 a pouch, quite expensive. Very useful, actually I'd say essential, for replanting roses where roses have grown before, but otherwise not vital.

Many thanks--that was the name I was searching for. I bought a camellia today and the nursery assistant recommended I use it, I'm glad I don't need to.

However........if I were to buy some, how long does it last after opening?

Worth noting that mycorrhizal fungi do not form a beneficial relationship with most ericaceous loving plants and therefore probably not suitable for camelia.

It would seem that only lime haters Rhododendrons, Azaleas, Heathers (Erica, Calluna, Daboecia and Cassiope), Blueberrries and Cranberries (Vaccinium sp.) do not benefit from Rootgrow. They have a relationship with Ericoidal mycorrhizal fungi.

Thanks for that, I'll keep my money in my piggy bank. However---does it keep once opened?

What, your piggy bank? I doubt it if its like mine, lol.

Pack says up to one year after opening, but only if stored somewhere cool and dry.

Thank you!