Smart, like Fifth Avenue

Planting plenty of the same thing is a nerve-wracking business, and risky to boot. There are three outcomes, really.
First, whatever you've planted is hugely successful and you spend the rest of your life watering, fertilising, thinning out and cutting back. Second, it's a complete failure and you spend the rest of your life digging out and replanting until you find something that works. Or third, you have a mixed result and spend the rest of your life replacing the failures and hoping the next lot will do better.
Truly, I can't imagine how orchardists, crop farmers, olive-grove owners and winegrowers stand the stress.
This is what puts me off planting an avenue. I'd love to have an avenue leading down our rather long driveway, but fear of failure means I now have something better described as a series of clumps of random trees. True to form, some have been hugely successful (acmenas and bottlebrush), some have returned a mixed result (vibernum and grevillea) and some, the names of which I have subconsciously erased from my memory, have failed miserably.
However, now that I have a real landscaper on board, I'm tempted to remove the hugely successful bottlebrushes, with their dry-looking foliage and grumpy pink flowers, and request something carefully chosen and well planned that will turn the driveway into a welcoming path to our door.
An avenue, according to a rather cutesy garden magazine I picked up recently, should be "an oasis of shade and shelter that leads to the heart of your domain".
It didn't mention anything about the depressions that bad drainage has caused, or the tangle of hideous bright green hoses that always seems to lie across the driveway (I'm hopeful someone will soon invent a gravel-coloured hose) or the occasional mistakes left there by the dog.
I don't know about the oasis thing, but I am sure we can create planting that will both broaden and lengthen the view. The idea is to attract the eye from side to side and to create the illusion of a roof between you and the sky.
Next, the trees should frame the view of the house, create an attractive vista, and disguise any unappealing elements, such as, in our case, the hen house, the ride-on under its bright blue tarpaulin, and the pile of building rubbish waiting to go to the tip. Quite a big ask, really.
Alternatively, the avenue can hide the view of the house until you actually arrive, lending an element of surprise.
Unfortunately, an avenue demands that all the plants be the same, which is a major effort in self-discipline. But the good news is this is an avenue, not a hedge, so they don't have to create an absolutely uniform barrier characterised by perfect angles and symmetry.
Nonetheless, the species needs to be selected with care so you get reliability and the right habit. An upright, vase-shaped habit with ascending main branches is typical. Weeping or spreading trees, lovely though they are, do not make an easy avenue. They will undoubtedly spread out on to the driveway rather than the other way and impede anything taller than an MG that tries to park underneath. You will never be able to take delivery of large pieces of furniture in big trucks, move house, or travel down the driveway in a horse-drawn carriage.
So give some thought to the trunks of your trees, since this is the part you'll probably see the most of. Something with interesting colour and texture is a good choice. Symmetrical, straight trunks give a sense of rhythm along a long driveway, but twisted trunks have a special charm, too.
To avoid the "complete failure" or "mixed result" syndrome, plant trees that will enjoy your climate. And you needn't limit yourself to typical avenue trees such as poplars - there are all kinds of trees that'll work, from ornamental pears, to olives, to camellias, to palms, to evergreen magnolias.
If you have your heart set on something that doesn't have an upright habit, find out if it responds well to trimming, and resign yourself to keeping it cut to the shape you want.
At the moment, I'm looking for something flood and drought tolerant that grows quickly, flowers, smells good and produces fruit. If I'm prepared to do without fruit, I may get away with an Australian frangipani, even though I will probably have to keep it trimmed. Watch this space.