Plectranthus can be indoors, close to a sunny window, or outdoors year-round in warmer climates. Place in full to partial sun while outdoors and on a sunny south facing window indoors or under a grow light for at least 6 hrs. a day.
Bonsai trees live in small pots and their world dries out much quicker than plants in the ground or in bigger pots, so close attention should be paid to watering. Check and water your bonsai every other day or so, until your tree is acclimated to its new home. Striking a balance between not enough water and too much water can be a bit tricky but is very important. Plants should not be allowed to dry out, but they can tolerate brief periods of drought.
The Plectranthus is very resilient and easy to care for. Once your tree is adjusted and you have the perfect spot and schedule where it is happy, your tree will bloom all year long. Bonsai mint does not really need to be fertilized, but you may give it a liquid fertilizer to induce production and bloom. Fertilizing once every 3-4 weeks with a water-soluble fertilizer with only ¼ of the strength suggested will help provide the nutrients your tiny tree needs in its small pot.