Better they be snug in good quality compost (not MPC) as this reduces evaporation from bare soil. Bear in mind that they will need daily watering once established and more than that on hot and/or windy days. They'll also need a weekly liquid feed to keep those flowers going till the frosts. Assuming they will be above head height, try the trick of sinking a small plastic plant pot in the middle of the basket to facilitate watering and help it go deeper down to the roots.