I've been watching your question here because I'm interested. It's such a nice opportunity to do something attractive. I don't know enough to make any recommendations. I always like heavenly bamboo, but there are probably other more interesting plants to use. I've seen some with variegated leaves, green and white, but I don't know the name. You don't just want an old green hedge! Hang on, maybe someone will have some ideas for you.

Sunny, how generous you are to share your idea, AND find those lovely example pics. While i love succulents, they are just not not the look I want here. Am leaning toward Rhaphiolepsis (ease of care, easy to replace, spring flowers, birds. Im still stuck on the limbed up shrub. Dwarf lime might be nice, but don't want to attract fruit loving rats.

About this size .

This look, with far fewer, smaller "trees", and no 2nd hedge in back, of course.

Have you considered the maintenance to maintain the standards in their shape? Unless they are a species of minimal size (azalea or euryops, for example, which are generally kept under 3'), they will be wider than the planter. It is fine if they stick through the fence, but will you have easy access to that side for pruning purposes?

How wide is the bed? It looks pretty narrow and you might not be able to fit as much as you are planning.

Bottlebrush cultivars are available in various growth patterns. The bloom most of the year and attract humming birds. They can also be limbed up into small trees with attractive, fissured bark.

Natal plums are commonly hedged to the size that you are looking for as well. They bloom pretty freely and have a nice scent similar to star jasmine. They are less aggressive growers than the raphiolepsis and would need less maintenance trimming. They are quite thorny.

What about trailing lantana or rosemary spilling over the edge of your planters?

ETA: Duranta is another small tree form that wouldn't be too much of a maintenance issue. I've never seen them much over 6' tall and they are certainly widely planted.

I beg to differ about the Duranta. I love them, and have had two different ones at two different houses, one of which was kept as a "small tree". But they are as vigorous as heck once they get established. You have to really stay on top of the pruning to keep them under 8-10'. I enjoy the flowers, then lop off enough 3-5' branches to fill half a green-waste dumpster every few weeks. Great plant that attracts both hummingbirds and butterflies, but not a plant I'd want more than one of to have to maintain.

ETA: I went out and measured; it is self supporting and currently 13' tall.

Callistemon 'Slim' has a vertical growth habit, but you don't have a lot of root room in that planter.

Rhaphiolepis is a good standard no-fuss shrub. There are smaller selections available.

So strange. I posted replies to your generous help on my ipad, but do not see them here. Also asked you let me know if you see them. Guess not. So again... Thanks to you all. And to blueskies. whose post has disappeared, i do like coffee berry! Jx Brown, prefer no flowers, though i love duranta. To gyr falcon, my neighbor, I think,( and hoovb, too:) There is access for trimming. Good point. Hoovb. Yes to rhapiolepsis( see upthread) , but need a different standard, i think, to mix it up a bit. I'd love to use your Coral Bark maple( do you remember my asking you about it years ago?). However, I question the location: coastal nw with full afternoon sun. But an evergreen like Bay Laurel would also be perfect if not for eventual size.

Have you seen the new Coprosma cultivars? They stay fairly narrow and none seem to be much more then 6' tall. Glossy,clean looking all year. Not called mirror plants for nuth'in!

Although these cultivars to be various other names..like Tequila Sunrise.

Darn. Images usually are closeups... Same with this. Sure would love to see it as a standard. Says brides to 10 feet. Perfect.

Mine was a wee gallon plant .Now in a 3 gallon. But I see larger being sold. Pest free.

I've never pruned it...its that pyramidal naturally.

A non-bloomer? That's tougher. Coffee berry is a painfully slow grower. I have mountain mahogany (Cerocarpus betuloides) against one wall. It's vertical and narrow, but also wispy and see-through. Mine hasn't bloomed in 5 years. Cerocarpus alnifolius is supposed to be a more conventional appearing hedge.