How to care for it. I live in Costa Rica and they grow here but I want to get rid of the mold. . . . how?
Powdery mildew is caused by a fungus. Neem oil can help with this. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm
Just been given poinsettias. Want to keep them alive. I live in north Florida. Have room indoors and outdoors.
These articles should help with their care: https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/poinsettia-care-how-do-you-take-care-of-poinsettias.htm
https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm
My poinsettia is getting black on the red leaves and the red and green leaves are falling off. What's the problem? It otherwise looks healthy.
I would check for pests. It sounds like your plant may have sooty mold, which is a fungus caused by insect pests, like scale or aphids. Neem oil is an effective treatment, both for the pest and the fungus. Here is mroe information: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
I have heard the first of Sept. or the last and can you use a growing light to help it change color?
For information on growing these plants, these articles should help: https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/poinsettia-care-how-do-you-take-care-of-poinsettias.htm
https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm
I live in the Ozarks of Missouri. I planted my Poinsettia outside and it has grown to about 3' x 3'. It is a beautiful plant and I would really like to keep it alive. Can I transplant it into a large pot? How large is the root system? Can I cover it with a dark bag at night? I don't have an area that is completely dark. If I can't bring it in, can I mulch it and let it die back to come back in the spring?
They typically cannot tolerate temperatures under 50 F. So if it gets colder than this in your area, you'll need to bring the plant indoors. Dig it up and gently shake off excess soil. Then pot it up in a container large enough to accommodate its roots, which may be trimmed if necessary. Also, it may help to prune the plant back some to reduce shock setting in from transplanting. Here is more information: https://www.gardeningknowhow.com/houseplants/hpgen/prune-roots.htm
https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/poinsettia-care-how-do-you-take-care-of-poinsettias.htm
I have one from last year that's done very well. It's in a pot. How do I force it to bloom by Christmas?
This article will help you with that: https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm
How long should poinsettia plants remain covered in order to force red leaves for Christmas?
This article will help you with that:
https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm