The leaves of my poinsettia are turning green. How can I keep them red?
There is no way to keep them red. They turn red on a cycle, like tree leaves turn colors in the fall. This article will explain how to make them turn red next year: https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm
I have one poinsettia that is about 2 feet wide and 2 feet high with about 20 blossoms on it. I have another large poinsettia that receives the same care as the first plant but does not blossom at all. The blooming plant is 2 years old and the non-blooming one is 3 or 4 years old. What do I do to make it bloom?
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
I have white gnat-like bugs living on the underside of the leaves on my poinsettia plants. What are they, and how do I get rid of them without harming the plants?
It could be whiteflies, though I am not positive. Nonetheless, I prefer treating these pests, and most others, with neem oil. It is very effective and safe. Here is more info: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/whitefly-control.htm
https://www.gardeningknowhow.com/plant-problems/pests/control-whiteflies-on-houseplants.htm
I found a cactus preparation potting soil by Miracle-Gro at Walmart which would allow a fast flush and adequate drainage of water. Is this an appropriate soil selection in which to pot poinsettias?
I would mix it 50/50 with regular potting soil. It is just a bit too free draining for poinsettia.
Why are my yucca leaves going yellow? Is it overwatered or not watered enough? Also, I have a poinsettia that I got at Christmas 2 years ago, which is now quite big but the leaves are a bit yellow. How often should this be watered, and is there something I can do to help it go red?
If the yucca is an indoor plant, it is likely overwatered. Water only when the soil is dry to the touch when your finger feels dry soil 10 cm down or so. You also want to make sure it is getting enough light.
This article will help you with getting the poinsettia turn red:
https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm
https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/poinsettia-care-how-do-you-take-care-of-poinsettias.htm
I have two beautiful plants that are healthy, huge with lots of green leaves. I want them to turn red for holidays. How can I do this? Should I put them in dark place now 24 hours? They get plenty of darkness at night.
This article will help you: https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm
Will a poinsettia survive if planted in sand?
I would mix it 50/50 with regular potting soil. It is just a bit too free draining for poinsettia.