My husband and I are in the process of buying a local nursery. They plant mums every year from seed. The last few years, (this year included), they have had an issue of only the orange mums dying. Any idea of what is going on?
I would examine the type of seed they are using. Is the orange seed coming from a different source than the other colors? There could be something different in the way the orange plants are grown. Do they get more water than the others?
I wonder if a certain pest is attracted to the color orange more so than other colors. Do you know what they die of? Is it pests or disease?
I did a little research, and apparently, this is not a common problem. These articles should help:
https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/troubleshooting-seedling-issues.htm
Should I put them in a dark cool place now or wait until they bloom inside and then store them. And what kind of environment will they need to make it until the spring?
Don't you want them to bloom outside? Mums will tolerate a frost. Your hardiness zone is 5, and mums are generally hardy to zones 4 or 5. I would bring them in tho if temperatures hit 32 F or below. If you want them to bloom inside, put them near a sunny window and keep them watered. After they bloom, remove the flowers, but leave 2 to 3 inches of the stems to protect the crown. To overwinter inside, you can store them in a cool, frost-free location till spring. Water about once a month, enough to keep them alive. Too much water will cause them to rot.
It may be a little late to plant them in the garden now, but in the spring, you can plant them in a well-draining area with full sun.
https://www.gardeningknowhow.com/ornamental/flowers/chrysanthemum/wintering-mums.htm
https://www.gardeningknowhow.com/ornamental/flowers/chrysanthemum/annual-vs-perennial-mums.htm
https://www.gardeningknowhow.com/ornamental/flowers/chrysanthemum/growing-chrysanthemum-flowers.htm
And will cuttings from a white mum grow white?
Yes, it should stay white. My white mum has returned for 20 years. There is such a thing as a "sport," which is a mutation that could result in a color change, but that is not the norm. A cutting from the plant should look identical to the parent plant.
https://www.gardeningknowhow.com/ornamental/flowers/chrysanthemum/annual-vs-perennial-mums.htm