Answer: The space you describe is a little too narrow for a tree of any kind so you may want to consider growing a shrub which you can train into a tree shape. Oleander is a suggestion; it remains evergreen and blooms throughout the spring and summer months. If you decide you'd still like to plant trees, here are a few suggestions:
Crape Myrtle (Lagerstromia indica) A tree with multi-faceted interest, crape myrtle has beautiful clusters of large crape-paper-like flowers in bright pinks, reds and white. Flowering is continuous from spring to fall. Leaves turn a bright red-orange fall color, and shed to reveal beautiful cream and beige pealing bark. Crape myrtle can be grown as a single or multi-trucked tree. Here in the desert it will obtain a height of 18 feet over time. It grows in an upright, spreading form to an eventual height of 18 feet.
Xylosma (Xylosma congestum) If your looking for a small evergreen tree with a dense canopy and "northern" look, then xylosma is for you. The leaves of this tree are dark green and the size and shape of cherry leaves. It is often sold as a shrub for training into a hedge, but plant it alone and prune the lower branches and it will develop into a very nice tree. The tree develops a mushroom cap shape and grows to a height of 15 feet with equal spread. This one's great for providing patio shade.
Mexican Bird-of-Paradise (Caesalpinia mexicana) This plant, often grown as a large shrub, makes an excellent patio tree when pruned to form. It has rich, dark-green leaves and unlike the yellow and red birds-of paradise, this one is evergreen. Very showy, bright-yellow flower clusters arise from the canopy and bloom nearly year-round. The Mexican bird is a fast grower, maxing out at height of 10 to 12 feet.
Narrow-leafed gimlet (Eucalyptus spathulata) You may have thought all eucalyptus were huge trees, but there are some excellent, small eucalyptus varieties as well. Narrow-leafed gimlet is a multi-trucked tree with attractive reddish bark and ribbon-like gray green leaves. It grows at a moderate rate to an ultimate height of 20 feet. Like its fellow Australian Eucs, it can take the desert heat and get by with infrequent watering. Keep in mind that all newly planted trees need frequent irrigation until they become established.
Good luck with your new landscape!
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