@squirral87k4-WvGwT It depends on what you mean by a tree. I think of that as a plant where the canopy starts about head height (5-6 ft). If you mean something similar to the Fatsia in the picture, then probably only a few years, if you buy a decent enough Pittosporum to start with.
Rather than buying a large Pittosporum, and cutting off most of the lower side branches (which will give you a very knobbly trunk), you would be better off buying a small plant, and giving it optimum growing conditions and care. That way it will hopefully put on lots of growth each year.
If you then start removing side branches when it is a young plant, and focus on having one single trunk, you shound end up with a more smooth trunk. Pruning the side branches will also encourage vertical growth.
Personally, I would go for a more dense, larger-leaved hydrid, if I wanted a tree, such as P. Garnettii, or P. Green Star. P. Silver Queen has a more fine, open foliage, but that's just personal taste.
@Athelas I love your Tandara Gold. We lost one many years ago, when moving it when it was a mature shrub. Much missed, it was one of our favourite varieties.
I’m not fixed on a p Silver Queen but I have very limited planting space and wanted a tree that was evergreen (variegated/silvery foliage is a plus) and with an “airy” feel so as not to make the space feel claustrophobic.
Thank you all for the helpful replies and great photos. All very useful and I’ve taken notes of the names of the trees as a backup.
@squireler Here’s a photo, it’s still very small. I have two at this height (but photo of only one) which started as one plant. Last autumn when I pruned it, I sawed off the very thick branch growing from the bottom of the trunk and planted it as a separate plant. Both are doing well despite being in such a narrow space. The idea is to keep pruning until the foliage reaches the top of the fence. The trunk isn’t straight but I prefer it this way.
@KeenOnGreen - thank you for the photos and advice. All very clear but how long do you think it would take to turn a pittosporum silver Queen into a tree? Online searches suggest it grows 40-60cm /year which seems quite fast ?
Thanks. I have lots of fatsias, they self seed all over the place. Will try turning one into a tree.
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Rather than buying a large Pittosporum, and cutting off most of the lower side branches (which will give you a very knobbly trunk), you would be better off buying a small plant, and giving it optimum growing conditions and care. That way it will hopefully put on lots of growth each year.
If you then start removing side branches when it is a young plant, and focus on having one single trunk, you shound end up with a more smooth trunk. Pruning the side branches will also encourage vertical growth.
Personally, I would go for a more dense, larger-leaved hydrid, if I wanted a tree, such as P. Garnettii, or P. Green Star. P. Silver Queen has a more fine, open foliage, but that's just personal taste.
@Athelas I love your Tandara Gold. We lost one many years ago, when moving it when it was a mature shrub. Much missed, it was one of our favourite varieties.