As much as I don't like to discourage anyone who wants to do something imaginative with natives, I can see heartbreak ahead if you actually plant E citriodora, (pleached or otherwise), in a small area. But since you have some seedlings, why not try keeping them in pots? They'd look lovely in large terracotta ones, for a few years at least, and, provided you've only tied the branches together, you could move them further apart as they get bigger. I'm sure you could sell them if/when they grow too large for you to manage. They should be worth quite a lot by then.
There are several dwarf varieties of flowering gums available now, I don't think any of them have straight trunks but you could ask at a good native nursery. A variety that grows to 3-5 metres should be able to be kept to 2 metres without too much difficulty. E. citriodora grows to 30 metres or more.
BTW, I've managed to keep 2 E.gunnii as standard specimens in pots for some years now.

I intend to have a bit of fun with these gum seedlings. My original idea was to simply cut them back to ground level each year or two--I view these as expendable plants. If they get out of hand--whether as plants that are coppiced or those that are pleached--I intend to cut them down. I once cut down a 10-y-o tree because its flowers weren't scented as described on the label. (It took 10 years to flower.) So I can be pretty ruthless.

I don't want to keep them in pots because I have well over 50 plants in pots already, and this is my first chance to plant out my own garden ... and have some fun along the way.

Has anyone else tried pleaching eucalypts?

Cestrum, I can understand why you don't want any more plants in pots, and, since you are prepared to be ruthless, then go ahead and experiment with planting them in the ground. We need more people like you who are prepared to try something different, especially with natives. I'm all for gardening being fun, especially when you learn along the way.
It's good to know there is someone else on this forum who is not afraid to move or remove plants which disappoint or have outgrown their welcome.
You might try posting on the "Native Plants" sections of this forum, there might be someone there who can help.

Dear Ruthless Cestrum

I like your idea, there is no doubt the smell would be lovely. Have you thought about what the roots might do ? Drains, pavers, concrete, will the roots affect any of those things ?

Another lovely smelling plant is Backhousia citriodora...but you probably dont want alternative suggestions...do you ? I just could'nt resist saying it...the thought of the smell is heavenly.

Pleach away.

I've been contemplating doing something similar with an excess of birch seedlings. If the tops are kept pruned will the roots spread as far? Would putting in a root barrier help? What about a raised garden bed with weepholes along the sides for drainage but root barrier at the bottom to stop the roots escaping, sort of like a large built-in flowerpot with an oversized bonsai in it? If it looks like not being very successful when they get to about 2-3 metres will they be too much trouble to dig out? I hate to let the seedlings go to waste but I don't want any more full size trees to try to keep going through another drought.

Yes, you're right Popi; I'm determined to have my way with these seedlings :-) Nearest structure is my garden shed, which doesn't worry me. If they send out roots, they'll probably head off in the other direction towards the veggie patch. But I'm fully prepared to cut them down and dig them out if they get out of hand. As I said, it's the first patch of ground that's been all mine, and this area is just lawn. Eventually I expect it will be given over to something else (maybe paving) but, for now, it's free for experimentation. When the garden gets established, I simply won't have room to try things like this.

Macbirch, I don't know about birch trees in particular but suspect that, as the roots are generally in proportion to the canopy, if you keep pruning the tops then the roots should never get too cumbersome. Perhaps you could try posting to one of the US forums. They have so many more members that you'll almost certainly find at least one person who has done, or tried, what you want to do.

The discussion on hedges has reminded me about pleaching. Saw the image below of a pleached oval of hornbeams in London and thought my little experiment with lemon-scented gum seedlings might look something like that--only *much* rougher. Still, it looks quite do-able, I think ...

Here is a link that might be useful: Pleached hornbeams

Oh, yes, this looked lovely and I would say it is worth doing. Yours is more like a topiary/hedge sort of thing that is much practiced in France. I did some search about pleaching and laying hedgerows, and I am thinking the same thing. I will just try. Fortunately I have an average block, not a courtyard to play with. I am thinking of laying my gum I have in front. I will cut it back to the ground and let it reshoot, with a few new straight branches about 2m high I can start pleaching. I also have a number of lilly pily seedlings, so I might try them as well. The gum will be a trial so we will see what comes up. Thanks to those who suggested pleaching, just something new to try in the garden :-).

Cestrum, of all the eucalypts, I reckon you have chosen the most unco-operative for pleaching. In your neck of the woods you have wonderful rainforest species that would be far more co-operative. Lemon scented gums have a very strong mind of their own. They just want to go up, up, up.
They also have a strong habit of dropping their lower branches.

Robert, I think the consensus is that (1) the lemon-scented gum is far from the ideal plant for pleaching; and (2) I'm gonna do it anyway, until I decide to get serious and give that part of the garden over to something permanant :-) (Which will happen while they're all still small enough to be cut down and/or dug out!)

I've had an email asking how the eucalypt-pleaching went. Sadly, it didn't! The lemon-scented gums were planted in a no-dig garden made of sugarcane mulch so, in windy weather, one by one, they toppled over! And my garden five years later is quite densely planted out, with the little remaining space devoted to growing out brugmansia seedlings. So I'm neither inclined nor equipped to try the experiment (i.e. actually pleaching them, as opposed to just growing the trees).