in a word....NO

patris,

Sycamore has poor rot-resistance. It'll
become a mass of fungi in a greenhouse,
even if sealed.

Thanks for the info. Shame as my plants would have looked so good against it!

How do you know this stuff???
What about mounting broms in a live sycamore? Or a liquidambar?
I saved the stump of a bottlebrush/Callistemon rigida I was planning to use to mount broms. Is this a bad choice also?

patris,
I would think any reliable local nursery or the folks at the places we buy our brom plants,or your local Brom.Soc. would know if there is a safe sealent to use.
Or,just try out a few pieces using unsealed,and some sealed with transparent oil stain (clear),or anything they might recommend at a Lowe's or Home Depot.There may be some new stuff available that is environmentaly friendly. Mount a few expendable tils and other broms,mounted on moss or mesh,and see how they hold up.Mount the tree wood to a solid flat base,like slate by drilling a hole in it,and fastening the wood to it with a strong wood screw or two.Seems like that would keep the wood from decay,at least for a long time. Might be worth a try.
Bob

Patris there is NO safe sealant for broms and the wood wont last...get driftwood, riverwood, or cork.....in the long run you will be a lot happier with the results.
as for box store knowledge...i would not depend on them for help past reading whats is printed on a package...they dont pay them enough to scholars

Catkim,

My advice is based on experiment and experience. About
25 years ago, I did some rot-resistance tests on various
trees for a "hippie" building project. For the last 30
years, wood has been my primary source of winter heat.
You learn very quickly which trees can be left exposed
to the elements all winter, and which ones must be put
under cover immediately. My knowledge is limited to
Eastern deciduous trees, and styraciflua (American
Sweetgum) is the only Liquidambar in that group. Like
Sycamore, Sweetgum is soft and porous, absorbs and
retains water like a sponge, and rots quickly. I can't
help you on the Callistemon rigida.

Patris,

Your Sycamore would be OK in a cacti/succulent planting
in an arid environment. But in a greenhouse with constant
high humidity? Even if you can find a safe sealer, checks
(drying cracks) will develop and allow fungal spores to go
where your sealer hasn't. On the other hand, you really
have nothing to lose. If the piece of wood totally rots
away, you'll still have your plants. I just like using
pieces that will still be attractive 4 or 5 years later.
And IMHO, Sycamore won't.

Here is a Sycamore of mine. It's only 12-15 years old,
so it hasn't developed that dazzling white yet.

{{gwi:450819}}

Thank you so much for all the info. I do have a rather large cactus bed that could use a little dolling up!