When I brought my plant inside for winter, all the leaves have dropped off.
You should bring the plant indoors when the temperatures are about 42 degrees F during the daytime hours.
A south facing window is best to give it plenty of light.
This light does not meet this sun lovers needs, but it should keep it growing through the winter.
Let the soil dry out between waterings.
You can also keep the plant in a cool location; between 32 and 44F. This will force your plant into dormancy. All the leaves will drop from your plant.
Water just enough to keep the soil from drying completely-once or twice a month.
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-in-containers.htm
Lack of flowers or buds on vibrant bougainvillea. Plants are in large pots and get watered by sprinklers. How can we force some buds/flowering? Plants get full Southern California sun.
Please see this article on how to promote blooms on bougainvillea:
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-not-blooming.htm
Here are some general reasons a plant may not flower:
https://www.gardeningknowhow.com/plant-problems/environmental/plant-not-blooming.htm
My bougainvillea bonsai seedling, approx 5", was doing great until I "pruned" it to try and keep leaves small. Now, it's very leggy with very few leaves and doesn't seem to be doing anything anymore. What should I do?
Lack of growth may be due to inadequate temperatures and light conditions.
The links below will refresh you on the care needed.
https://questions.gardeningknowhow.com/tag/yucca-plants/
http://www.mykitchengarden.info/2014/07/bougainvillea-bonsai-making.html
Pink bougainvillea flowers are turning to a grey-like colour. Not sure if that is a sign of over or under-watering?
It is difficult to say, without seeing an image of the plant.
Greying of the blossom color could be due to aging of the flowers.
Browning of blossoms could be due to watering issues, disease, lack of sun or other environmental issues.
Soil should be well draining and the roots should never sit in soggy soil.
Here are some links with care information that may help you pinpoint the issue.
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-in-containers.htm
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-garden-care.htm
This is my bougainvillea plant that was outside this summer and bloomed very well, but since fall I have brought indoors but the leaves are falling and the stems look dry. First I thought the leaves were falling due over watering so I cut back, now the leaves look green but frail and still falling, even the small stem that caught root (in pic) had 2 leaves but they also fell off. Any advice will be appreciated. Thanks
Your Bougainvillea should be placed in a south facing window while indoors.This light intensity is less then it would receive outdoors but it should keep the going through the winter months.
Water your plant when the soil dries out slightly. Make sure the soil is well draining.
You can also place the pot under a grow light in addition to the sunlight.
https://www.gardeningknowhow.com/houseplants/hpgen/what-are-grow-lights.htm
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-in-containers.htm
My Bougainvillea bush got hit with frost in Houston and it is totally brown. I would hate to lose it. What can I do or is it a lost cause? It's pretty big.
Wait until after the danger of more frost has passed. The damaged parts of the plant actually may help insulate the plant.
When the danger of cold and frost has passed you should trim the plant back to healthy parts of the vine, making sure you cut a leaf node.
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/pruning-bougainvilleas.htm
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-winter-care.htm
The leaves on my potted plant dropped off and are slow to grow back, it looks very spindly, I'm still getting blooms though.
Check the plant for loopers, they can devour the leaves quickly on a Bougainvillea.
Here is a link for what to look for.
https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-loopers.htm
Over watering is the most common reason for leaf drop. They do not need a great deal of water so make sure the soil is drying between watering.
If watering is not the issue, check for Aphids. They too, are commonly found on Bougainvillea and can be treated with Neem Oil.
Lack of sunshine can also cause leaf drop. Adjust the light if your plant grows in a pot.
When the weather is cooler your plant will also drop leaves.