I think you did use a balanced fertilizer but the slow release plant food does not immediately pump fertilizer into the young plants. As the weather heats up and the soil warms more fertilizer is released just as the plants need it the most. To jump start the process use a liquid plant food like Miracle Grow that will get to the plant immediately. Plants even absord a water soluable plant food like this throught their foliage. For container gardens that are overflowing with blooms I use Osmocote in my potting soil and then also water with Mircacle Grow a few times during the summer season. Enjoy the those hanging baskets this summer and Keep Growing, Marianne Binetti