Potting mix for (shady) container

WildFlower_UK

I've got a selection of shade/semi-shade loving plants to be planted up in 40x40cm square containers (with drainage holes). In each container will be a fern, sarcococca and vinca minor.

What would be the best sort of potting mix for them? The containers are in the shade of our house and although not directly against the wall (roughly 1m and 3m away), I expect being the shade of the house (for most of the day, they do get some early morning and late evening light) and also being in fairly full containers, they are not likely to get a lot of rain on the soil (which obviously also lacks in the summer). So something moisture retentive? 

Any suggestions helpful

K67

Potting mix for containers in shade or sun would be the same. You can buy specific container compost with water retaining gel or use a ordinary multi purpose plus John Innes 3, perhaps chuck in some leaf mould if you have it or well rotted manure and a spadeful of garden soil as it's more 'alive'

punkdoc

If you intend them as permanent plantings, I would do a mix of JI 3 and MPC 50 / 50.