For instance, my pansies. I buy them in bloom, plant them in the yard, and they stop blooming. Check the light situation. If they are growing in too much shade, you will get a nice plant with little in the way of flowers.
Pansies do best in full sun.
Other reasons for lack of blooms, can be too much nitrogen which sends the plants into foliage production often to the exclusion of blooms. With a diverse group of plants not blooming, I would suspect a lack of sunlight. In early December I planted pansies and used approximately 1 teaspoon of bone meal per plant. I have watered them when it was dry, but the plants have hardly grown. Pansies are heavy feeders, and respond well to nitrogen.