When you buy bagged compost, planting mix/soil, potting mix/soil, composted manure and all the other sterile products available, check the fertility and pH on the bag. Do they advertise it to be 2-10-3 or 10-46-0? Is the pH (acid - sweet) level high or low?
Geraniums and pentas prefer a high pH requirement (6.3-6.5) and pansies prefer a lower pH (5.5-5.8). The wrong planting soil and amendments could lead to a disappointing result and providing the right environment can give you a gorgeous result.