I see there are a lot of different trees on here but I have not seen any Blueberry Juniper Trees. You can buy a Preserved Blueberry Juniper at several places. It is sold by the pound. It only difficult part is pulling all the blueberry's off. But they make nice natural looking armatures for trees. No painting or flocking required.
I have several trees that are 4 years old and still look new. I have started sealing the Juniper after the tree is finished. I make the trunks from Cedar and then cut and attach each piece of Juniper. i drill a ole and glue with CA. They look really nice when done..I have me all over my Layout..
This is a picture of them just finished not in place. These are between 18 and 24" tall.
I think the Blueberry Juniper could be used for O scale.
The trunks take the longest to make.
Here is one I did for a clinic last year. It would be 62' in O scale or 16" tall. The trunk could have been a little bigger diameter.