Answer: I'd plant a shrub in the planter. Start by loosening the soil and adding a bag of compost, digging it in to a depth of 8-10". Then thoroughly water the planter to make sure the soil is moist before planting. After planting you'll need only to water once a week. Here are a few suggestions for medium sized shrubs:
Compact European Cranberrybush Viburnum (Viburnum opulus 'Compactum'); very adaptable to sun or shade; flowers in spring; grows 4-6' tall.
Carolina Allspice (Calycanthus floridus), same as above except can reach 8'.
Glossy Black Chokeberry (Aronia melanocarpa), same as above.
I mention these three shrubs because they are very adaptable and very hardy so you won't have much maintenance.
Best wishes with your planter!
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