If Bougainvillea is allowed to climb on Live Oak trees will it kill the tree?

No.

Can you elaborate?

My local Master Gardner says "The roots of the flower would not be able to get through roots of live oak; the flower would not thrive or survive; flower also needs sun- not much available under a live oak."

Thanks!

A neighbor has a bougainvillea growing up through a huge orange tree. Both are thriving.

I have big, old bougainvilleas growing under the branches of a huge, old live oak. I have no doubt that the bougies would probably do better if they weren't competing with the oak tree for water and nutrients, but it seems that as long as I fertilize in the spring, water weekly in dry spells, and prune them appropriately, they do fine.

Bottom line is, you really don't want a bougainvillea to grow to its full potential, The pruning job is a bear, as they are extremely thorny. So growing them near live oaks just helps to keep them in check somewhat. They do want sun in order to bloom well, though so you should try to keep the oak branches pruned back some, over the bougies and plant them on the south side of the tree if you can so they'll get full sun in winter.
This is one of my 3 huge bougies. See the oak branches in the top of the picture? One huge oak tree is about 20ft. away to the left, and there's another to the right about the same distance. Oak tree roots are under every inch of my garden, needless to say.

I agree, Bougainvillea do fine under Live Oak trees. We have one beneath a live oak that I keep chopping back, trying to kill it, I really, really detest those thorns! The former homeowners planted one right next to the walkway up against the house too and the trunks of both are so big that it's impossible to dig them out so we keep chopping away at new shoots.

This is a photo from a few years ago in a friends backyard; they have huge Bougainvilleas planted beneath, and growing way up through a couple of their live oaks.

The thorns are incredible, during a fellowship at a large garden, had to prune the Bougainvillea, wore a leather apron, gloves and chaps with a full face plastic glass. All the while on a ladder or in a gondola. Not fun, but beautiful plants. Even after doing that, I planted several on my fence in CA.

Thank you so much for your wonderful advice.

Several years ago my mom and I visited a place in Florida where they had Bougainvillea growing on Live Oaks. I don't remember the name of the place, but I think it was near Orlando. It was a beautiful site!

The sight of all those beautiful trees overflowing with color gave me the idea for my site. It is the site of the original High School in my little home town. I'm not a very good photographer, but I've attached an image of part of the property showing the Live Oak trees where I'd like to grow Bougainvillea.

I know this will require maintenance especially if we get a freeze. We're in zone 9b like Sebastian, Florida. We got two days of 25-degree weather a few weeks ago that killed unprotected Bougainvillea to the ground, but I think they'll come back.

Anyway, I'm the president of a nonprofit. We will secure grants to cover not only installation, but also regular professional maintenance.

I just don't know of another plant that provides so much color & beauty so many months each year in zone 9b.