Allow the soil get dry in between each watering. Test the soil by poking your finger into the top inch. If the soil is dry all the way through the top inch, provide the flowers with enough water to dampen the soil without soaking it. 3. Fertilize your geraniums once a month using a liquid fertilizer. An abundance of fertilizer will cause your geraniums to produce many strong, healthy leaves, but it will also prevent blooms from developing and may lead to a plant with minimal flowering. You can also use a slow-release, granular fertilizer.