From our perspective as Calibrachoa plants, we want nothing more than to produce a spectacular cascade of blooms for you. When we don't, it's not out of stubbornness, but because our fundamental needs aren't being met. Here are the primary reasons from our point of view.
We are sun-worshippers by nature. Our flowering mechanism is directly fueled by the energy we capture through our leaves. When you place us in a spot with less than six hours of direct, unfiltered sunlight per day, our survival instinct kicks in. We must divert all our energy into maintaining basic leaf and stem function, leaving no surplus resources to create flower buds. It is simply not a sustainable expenditure for us under low-light conditions.
What you feed us is critically important. A fertilizer with a high first number (Nitrogen) promotes vigorous green, leafy growth. While this might make our foliage look lush to you, it signals to us to focus on vegetation, not reproduction. We require a balanced or bloom-booster fertilizer (e.g., 10-15-10) that provides higher levels of Phosphorus (the second number), which is the key nutrient that supports the development of our roots, flowers, and fruits.
Our roots are incredibly sensitive to their water environment. If you allow our soil to become completely desiccated, we go into survival mode, and aborting flower buds is a first response to conserve water. Conversely, if our roots are constantly sitting in saturated, oxygen-deprived soil, they begin to rot. A compromised root system cannot effectively uptake the water and nutrients we need to support any flowers, leading to wilting, yellowing leaves, and certainly no new blooms.
Our biological purpose is to flower, set seed, and ensure the continuation of our genetic line. If you allow our spent flowers to wither and form seed pods, our mission is accomplished, and we will slow down or stop producing new flowers. By deadheading—removing the faded blooms before they can develop seeds—you trick us into a state of perpetual failed mission. We will continuously produce more flowers in a relentless attempt to create the next generation, which results in the prolific blooming you desire.
Extreme heat, while we enjoy warmth, can cause us to shut down and conserve energy. Furthermore, we are vigorous growers and can quickly exhaust the available space and nutrients in our container. When our roots become tightly wound and crowded (root-bound), our ability to absorb what we need is severely restricted. This creates immense stress, stunts our growth, and halts flowering as we struggle to merely sustain existing foliage.
