Ask Mr. Smarty Plants

The Flower most commonly referred to as stock is Matthiola incana which is a non native. It hails from southern Europe. The Lady Bird Johnson Wildflower Center helps to promote and protect native plants so we cannot offer real expertise with non native species, but will try and answer the question with some basics.

Stock is most commonly listed as an annual, but it can live for several years as a hardy annual and some states list it as a perennial. It is hardy to about five degrees fahrenheit, it is not frost tender. Denver Colorado is listed as right on the cusp of what a stock plant can take in terms of cold so you might be dealing with a plant that just isn't going to behave as a hardy annual or perennial. You may have to replant these plants annually to really get the most out of the species. Another common issue with plants producing buds and then dropping them before they open, is the lack of fertilization or some times over fertilization. This is a common problem with non native plants. You are trying to fool this plant into thinking it is growing in southern Europe and it just isn't so you have to manipulate its soil, light and food to make it happy and that's a tedious task.

There are some fun natives that have a similar appearance to Matthiola incana that you could have in a pot that are perennial. Two are blue only, but they are pretty cute. Delphinium nuttallianum (Delphinium) and Delphinium barbeyi (Subalpine larkspur). The other has a paler color, light to fairly deep pink Penstemon jamesii (James's beardtongue). The advantages of planting natives over non natives are numerous but for your specific problem you will find that these plants will out live your stock and you won't have to fuss with soil amendments or heavy fertilization. 

Lastly, you mention that your plants are in your home. If the pot is in the house you have a whole other set of problems. Neither stock nor marigolds would be truly happy indoors, even in Colorado. If you are looking for indoor plants then check in with your local nursery, they should have plenty of indoor plant suggestions. The difference between the two has to do with temperature, light requirements and dormancy. Indoor plants have been bred specifically to grow in a controlled environment and if this is where your pots are, then skip the suggestions above and grow some plants that can live indoors, there are plenty of blooming options for you.