At its best:
May, Jun, Jul, Aug, Sep
Put a layer of crocks in the bottom of the container, to stop compost falling out of the drainage holes.
Fill the container two-thirds full with compost.
Add slow-release fertiliser granules to the durface of the compost, and mix them in with your hands.
Plant the heucheras first, then the violas. Add more compost around the plants and firm in well. Water plants thoroughly and allow to drain before moving the container to its final position.