Can you bring it in the house? If not, cut it back to around 6 inches in the fall and add 2 inches of mulch to protect the roots. Mine was fine and grew like crazy the following year. It sounds like it got too cold in the garage and it is a tropical plant.
I read somewhere online about removing leaves from branches to start a formation of the bonzai. I realize it is a personal preference as to the shape one is trying to achieve. I have a thirty year old that I have been pruning or trimming to my desired shape. There is a 24" circle the bottom is 30" from the ground . The circle is made from several branches from which I have removed some of the leaves and there are a few flowers, leaves and I have removed some of the leaves from some of the branches.
I'm not clear on your question, but this link may be of help to you with your Bonsai.
why did all the leaves and flowers fall of my bougainvillea and what can i do about the problem
Flower and leaf drop could be due to stress, pests, disease or watering issues.
Look for signs of issues on the leaves and plant. Do you see pest or holes in leaves?
Is the soil wet and soggy or dry?
Is the soil well draining?
Is the plant in the correct location?
This article will help refresh you on the care requirements.
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-flower-drop.htm
Bougainvillea: how much to water?
Once your bougainvillea is established, it doesn't need much water. As long as there's some rainfall it should take care of itself - just water it during periods of drought, if it's wilting, or if you're growing it in containers. This article should tell you more:
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-garden-care.htm
I was recently given this plant when my Mother-inlaw passed, I would like to know what it is and how to care for it thanks in advance :)
Thanks abunch :)
It looks like a Bougainvillea.
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-garden-care.htm
one of my three bougainvilleas has wrinkling/crepiness on the new blossoms and leaves. What causes this? What should i do? Sharon Cunningham
This could be a sign that the plant got to cold. It may also need fertilizer. This article may help
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-flower-drop.htm
We live in the north of England and have had a Bougainvillea in a pot for around 10 years. It is kept in a south facing conservatory so gets plenty of sunlight. It's autumn here and we have had a sudden leaf drop, not surprising in autumn you may say, but we do not recall this happening so suddenly in previous years. Is this normal or do we have a problem?
More than likely the possibility is that the plant may need some fertilizer. Use an all-purpose fertilizer and some dolomitic lime, and that will help some. I would look, next, to some sort of small pest. Many mites are hard to see, and will cause that kind of damage. Here is an article that will help: https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-garden-care.htm