Bonsai need constant care. Most bonsai growers I know here in South India keep their bonsai on a  rooftop terrace to catch the maximum sunlight. Fertilizing fortnightly seems satisfactory for my bonsai ( they are all very young!) . I also pinch some of the shoots which get too long, especially the bougainvillea and the casuarina , which I want to look bushy, and not sparse as they do if left to grow naturally.