I've had excellant results with Camphor Trees. They will block your 'view', plus look nice the year round. They will get to be quite large - wide and tall, and could be pruned UP to accommodate the gate when they get big enough.

Scout around your neighborhood, schools, etc., for trees that look interesting to you; then, go to your local nursery for info on them. Check out some maples, oak or ficus. Camphor is a beautiful tree, but I wish I didn't have any close to me. There's one in the street and one in the backyard that's grown between my fence and the neighbors. Aside from the litter (leaves and branches), which shouldn't be a deciding factor, the Camphor tree reseeds all over the place! The seeds will get all in your flower beds, lawn, drains, etc. Pepper trees might also be an issue.

Ficus retusa ssp. nitida aka Ficus microcarpa will make a dense screen easily that tall in just a few years. Bear in mind that you will have invasive roots eventually that will push up pavement and other hardscape. Plant a row and keep it trimmed as a tall hedge. A large tree will take over your yard and you won't have room for anything else.

Here is a link that might be useful: A tall, dense hedge

Thank you for your feedback!

Westelle - Does your Camphor shed leaves at any point? I have been told they are semi-deciduous but have also been told by some people that they have not seen them shed leaves. Shedding would be a problem since it would not provide the screen we are looking for. How is the density of the foliage? Can you see through the leaves and branches? Also, have you had the problem eloise_ca mentions about it reseeding everywhere?

hoovb - How does Ficus retusa compare to Benjamina? Are they both equally dense? Which is better? If we plant a Ficus I would definitely make sure we put down a root barrier. Would that solve the problem of the invasive roots? Because I certainly wouldn't want them to tear up our garage or the neighbor's garage. The problem with a hedge is that we would have a gap where the gate is and would still see the ugly 2-story building. What do you mean that a tree will take over the yard? I am okay with a lot of foliage but wouldn't want it to prevent me from planting other things.

Anyone - I am also looking for a way to reduce the traffic noise from the busy main street. Does anyone have input on that? Also, what do you think about having two different trees on each side of the gate vs. the same kind of tree?

Thanks very much!!

I have a Cinnamomum camphora in front yard and hate it. It sheds twice a year for about 6-8 weeks each time. Each week before mowing I have to pick up branches from 6 inches to 2 feet in length and all the leaves. Then in Jan-Feb it has black colored berries that stain the driveway and sidewalk and also bird droppings in black everywhere.
I do see new little new trees trying to come up and I just yank them out.
It doesn't give me any shade since it's on the NNE side of house so it only shades the street. Sometimes I wish it would die so I could put something better in but to remove it costs big $.

They are planted in between the street and parking lot at work and people are always complaining about them.

I have a Celtis australis further up on the back slope but it gets much bigger than you may want and it also suckers. It provides lots of shade and twice in 6 years it also has black colored berries. So its also something else for you to probably avoid since its deciduous.

Podocarpus, maybe?

WOW! We must have had well-behaved Cinnamomum camphora... 5. Our trees would lose only their old, old leaves in the Spring, never becoming bare at all; (altho', one year, they seemed to be losing alot of leaves in late summer, which was found to be caused by a lack of water because of an irrigation problem. Problem fixed and new leaves grew.)

Maybe we didn't have all the litter problems because we kept the trees well-pruned... for 'form' in our case. There is some seed litter, and occasionally a seedling would show up... but easily pulled. Maybe our large bird population ate most of the seeds.

The denseness is 'soft', ei: not 'hard' like a wall of cedar or other dense hedges, but you don't see much behind the tree. We started out with larger trees.... maybe 10' tall and as wide, because we wanted instant coverage of the view of our garage doors from the driveway. After 15 years they were at least 20' tall and 16' wide. Also, they were multi-branched at ground level and not 'lolly-pops' when we purchased them.

Good luck with whatever look you choose.

Ficus retusa compare to Benjamina? roots are not quite as aggressive.

What do you mean that a tree will take over the yard?

i mean the yard ends up so shady and the ground ends up so stuffed full of roots that nothing will grow except Clivia. I do tend to think long-term. Probably you will move before then and a huge tree will be someone else's problem.

Look at Lophostemnon confertus aka Brisbane Box rather than Camphor. The roots are much better behaved and growth is rapid, though density takes a few years to achieve. No reseeding and litter is pretty minimal.

reduce the traffic noise from the busy main street.

A berm of earth planted with shrubs between you and the street is the most effective. Much of the noise actually comes from tires; a soil berm absorbs the tire noise pretty well. However you will have to see if it is legal to have a soil berm (possible visibility or drainage issues). Foliage helps only a few decibels. A fountain with splashing water helps mask the roar a bit. Good luck with your project.

Um, do you need a tree with a 50 foot diameter? All the trees you mentioned except the olive, will get that wide. That is as big or bigger than most LA backyards. Maybe look for narrower trees and shrubs. What is your water situation? Will these be in a lawn? Will they get no water after establishment? Since you are in LA take yourself out to the LA Arboretum, Descanso Gardens and the Huntington to look at mature trees before it gets too hot.
There are a lot of possibilities. Bamboo, palms, pines, citrus, avocados, eugenias, bananas, eucalyptus, tabebuias, tecate cypress, catalina cherry, Garrya, yuccas, Strelitzia nicholae, Podocarpus. Decide if you want something that does double duty with edible parts, flowers, scent, wildlife benefits etc. Decide if you want to water it or not. Decide what kind of canopy you want. For instance Cinnamomum, Ficus and Morus produce deep shade unless heavily pruned out. Queen palm produces light and variable shade valuable to many understory plants. Strelitzia is narrow and won't produce much shade at all. Check out the Cal Poly site below.

Here is a link that might be useful: Calpoly selectree website