Same with date palms.

It really depends what you plan to grow on the trees. High light you do better with Palms. More shade, any tree with a leaf canopy. I have a bunch of Phals, a few Dends, Aerides, Brassias, growing under a Loquat tree. Loquats form a dense canopy. I have a large Date Palm which has the pockets Harvey mentioned which is great for small divisions of higher light orchids.

Choose your trees depending on what you like to grow. Check the light levels of those orchids and plant accordingly.

Jane

We have very harsh summer sun and low humidity, so I'm thinking open canopied deciduous trees would be best. I like the palm idea, but any orchids would still need protection from strong afternoon sun. Sabals grow very slowly here. Livistona australis might be a better option.

tree choice is important and the rougher the bark and more open the canopy, the better chance you have of providing a suitable growing area for orchids. More important is the question of how are you going to water these plants?. Especially if you want to grow vandaceous plants in very low humidity environment. If you want to simulate a tropical setting for your vanda attached to a tree, you will to have provide substantial amount of moisture to plant, several times daily. The plant itself will show you that it needs more water when it starts loosing the older leaves as it adjust to a lower water intake than it needs to grow larger. This should be interesting, pls post some pictures and updates so that we can provide further guidance if necessary

Most trees are suitable. I grow quite a few orchids on a pretty wide variety of hosts. Here in California though I wouldn't recommend putting a thirsty orchid on a native tree. Natives aren't very fond of much water during summer.

Here's a list of hosts that orchids naturally grow on.

I've been looking closely at trees around the city. Cockspur corals look like they'd be perfect. Look at all that moss.

The other ones that look to have nice gnarled bark are the Bauhinia variegata and candida.

That moss is pretty nice! I've had very limited success getting moss to grow on my Cedar tree. I don't think that the bark retains enough moisture. But most of the orchids that I've attached to it don't have any problem growing on it. And I've even managed to germinate some Laelia anceps seeds on it.

Maybe around 7 years ago I planted a couple 15 gallon Pyrus kawakamii trees because they get really rough bark. But they seem to grow too slow. Only now are they starting to get large enough to attach orchids to. I do have a Vanda coerulea hybrid that's already nicely established on one.

Here are lots of photos of orchids growing on trees. Relatively few of them show the host and its orchids blooming at the same time. On the one hand it would be impressive to have a super spectacular living bouquet. But the other hand it's nice to have something different always blooming on a tree.

Here's a photo of a hybrid Cattleya blooming on my tree. They make a decent show but... the color is too light to really grab people's attention. Also, the flowers never end up naturally pollinated. I wish that I had attached something like Sophronitis cernua or LC Rojo instead. The first is naturally pollinated by hummingbirds and I'm guessing that they'd sure try and pollinate the second. Ideally the hummingbirds would make all sorts of crazy crosses and the seeds would germinate everywhere.

Wow. That is pretty cool about the germinated seed. Good stuff.

Callery pears are quite commonly grown here. They seem quick growing and might be a good choice. The low chill nectarines I planted previously also grew very quickly. I am thinking a flowering ornamental type might be more practical. Or possibly a donut peach.

I think deciduous trees will be better than evergreens which might cast too much shade.