I've heard that shoestring acacia is really good for tight spaces. And it doesn't seem to need pruning. Considering your small yard, definitely don't put in a mesquite tree.

I love my shoestring acacia, Acacia stenophylla. It will stay a tidy size if you give it moderate water, and is a graceful, lacy tree. Good suggestion Transplant.

Shoestring Acacia, would be a good choice for a small yard. Not a wide tree, and the form is nice. I also like Willow Pittosporum, Pittosporum phillyraeoides. Nice tree for a small space, also willowlike. The bark is whitish, and flakey, making an interesting contrast. There is one next to the Archer House at the DBG. Both of these trees would be a good choice.

My neighbor has an Ebony that's very nice. Slow growing. The other neighbor has a Mimosa... I read that they grow rapidly but hers seems to be slow. How about a cluster of Crape Myrtle TREES. Only thing with those is the leaf drop in the winter which could compromise the "screen" from the Apt. bldg.

A swan hill olive would be a great choice-moderate growing, evergreen, extremely tough and gorgeous form. A weeping bottle brush would also work-really pretty deep red flowers in Spring. Jacaranda is another possibility-you can keep it prunned up high to allow you to walk under it. Citrus trees would also work-avoid lemon since they grow the fastest, but Oranges would do very well. Generally speaking the native desert trees and acacias aren't going to give you very much "dense screening". Overall I'd go with the Olive since it is by far the toughest and will give you thick evergreen privacy year-round.

How about these?

Cascalote (Caesalpinia cacalaco)
15 x15 feet at maturity
Full sun
Young trees are very thorny
Stunning yellow winter flowers followed by colorful red seedpods
Low litter

Feather Tree (Lysiloma microphylla v. thornberi)
15x15 feet at maturity
Full sun/Partial sun
No thorns
Sensitive to the cold
Beneficial to native wildlife
Small white puffball flowers from May to June (flat seedpods follow bloom)

Mastic tree (Pistacia lentiscus)
15 x 20 feet at maturity
Full Sun
No thorns
Evergreen tree with stiff, dark green leaves turn red in the fall.
Low litter

Sweet Acacia (Acacia farnesiana)
20 x 20 feet at maturity
Full sun
Thorny
Sweet-scented flowers lend nice winter color
Beneficial to native wildlife

Texas Ebony (Pithecellobium flexicaule)
20 x 15 feet at maturity
Full sun, accepts some shade
Dark green leaf color all year
Thorny
Beneficial to native wildlife

Vitex (Vitex Agnus-castus)
20 x 20 at maturity
Full sun
Dark green leaves spring to fall (deciduous in winter)
No thorns
Spikes of purple (or white, pink) flowers all summer, attracts butterflies

aztreelvr suggests:
Feather Tree (Lysiloma microphylla v. thornberi)
and I highly recommend it as well.

I've had mine for 20 years and it gives great filtered light, a nice fresh green accent to the desert landscaping, and has a graceful shape. The yard Verdins love it. The only (small) drawback is that it looses most of its tiny leaves in the spring -- but give it 2 weeks and some water, and they're back for the rest of the year. Never any pests on it.

Zill

screwbean mesquite(20x20)

Instead of a single tree, how about a hedge of some type. I am thinking specifically of Italian Cypress. Italian cypress will grow straight up. While mature ones can get pretty tall, but they aren't much more than 6' wide. That way, it will be able to maximize the space you have available.

A couple of other suggestions for small trees are the flowering plum (15-30' tall--12-15' spread), pomegranite, and the fig tree. The latter two are quite drought tolerant and the fig and flowering plum are both decidious.

Vines and shrubs can be trimmed as trees. Some of these choices include pyrocanthea (sharp thorns, white flowers in spring and red berries in the fall), Duranta, yellow oleander (Thevetia peruviana), and even orange jubilee (Tecoma sp).

Good Luck and HTH

In my small front yard with direct sun, I have an Acacia saligna. My yard is only about 15 feet from my porch to the sidewalk - the tree covers it, but is not hanging over either the porch, or the sidewalk. It is extremely fast growing, only 2 years old and almost mature size, and has provided lots of shade and privacy. I have been able to keep it well shaped very easily.
I also have 3 Desert Ferns. I started with one, and when that established and started showing it's true beauty, I went out and bought 2 more. They can be shaped and pruned to either be a true "tree" shape, or left with multiple trunks for more privacy - I absolutely love these trees!

I took the liberty of copying the suggestions and descriptions posted by AZTreelvr on this thread and the other thread regarding a tree buying question and created a FAQ. This might be helpful for future questions.

Thanks!

Susie

Uh uh, thank YOU!

WOW!! so many great ideas...thanks everyone for helping me out. i think that we're going to go with the shoestring acacia. it seems to be the perfect tree for my little yard,since it will require minimal, if any, pruning.

http://www.desert-tropicals.com/Plants/Fabaceae/Acacia_stenophylla.html

not sure if its same shoestring acacia, it says
Growth Habits: Large shrub or tree, with a weeping habit, up to 20 to 25 feet tall (6-7.5 m) or more, 20 feet spread (6 m)

Friend of mine has one probabaly 8-9 feet tall, keeps falling down to neighbours yard during strong winds, they need to be secured to withstand winds.

My Shoestring doesn't have any problems with wind. Maybe your friend's has been overwatered or staked improperly when it was new. Not sure what you mean that it is doing, is the trunk bending or is it loose in the ground?

Bet it's a watering issue - they're very drought tolerant.

Every Acacia in my neighborhood has fallen over - some multiple times. I believe it's the way the landscapers installed the drip systems - the trees are all on the same systems as the shrubs so are getting more frequent and more shallow water. When I replaced my shoestring with the Saligna we ran another drip timed specifically for the trees, and guess what- after 2 years it is still upright!