Once the weather turns colder and you need to bring your brugmansia in from the cold, you have two options for over wintering your container brugmansia.
The first is to simply treat your container brugmansia as a houseplant. Put it in a sunny location and water as the soil dries out. You probably will not see any flowers while your container brugmansia lives in the house, but it has nice foliage.
Your other option is to force the container brugmansia into dormancy. To do this, put your brugmansia in a cool (but not cold), dark place, such as a garage, a basement or a closet. If you would like, you may trim your container brugmansia back by about a third before you store it. This will not hurt the plant and may make storage a little easier for you.
Once the plant is stored, water it sparingly, only about once per month. Be warned, your container brugmansia is going to start to look pretty pathetic. It will lose its leaves and some of the outer branches may die. Do not panic. As long as the trunk of the brugmansia tree is still green, your container brugmansia is alive and well. The tree is only sleeping.
A month or so before it is warm enough to take your container brugmansia back outside, start to water your brugmansia more frequently, about once a week. If you have room in your house, bring the container brugmansia out of its storage space or set up a fluorescent light bulb to shine on the brugmansia. In about a week you will start to see some leaves and branches start to grow. You will find that your container brugmansia will come out of dormancy very quickly.
Once you put your container brugmansia back outside, its growth will be very rapid and you will have a lush, breathtaking, flower filled brugmansia tree again in just a matter of weeks.
Read more at Gardening Know How: Potted Brugmansia Plants: Growing Brugmansias In Containers https://www.gardeningknowhow.com/ornamental/trees/brugmansia/growing-brugmansias-in-containers.htm