According to Jewish lore, the best time to plant a tree is 18 (“chai”) years ago, while the next best time is today. If not today, how about this month? April 28 is National Arbor Day, so you have some time to plan and get ready to celebrate. But how do you select that perfect tree for your yard? There is no easy way to answer this question! There are simply too many variables, not the least of which are your personal aesthetics.
The first question is, what soil type is your yard? We have sandy soil along the Cañada del Oro or the Santa Cruz River, rocky soils on the bajada slopes of the mountains, caliche on the valley floors, or who knows what fill dirt used to level your lot. Some species prefer different soils.
Second, around Tucson microclimates vary widely. There can be icy cold winters along the Tanque Verde Wash and Rillito River, yet it rarely freezes along Orange Grove Road. There is above-average rainfall along Pusch Ridge, and below-average rainfall in Avra Valley. Some trees do not tolerate freezing.
Third, what are the microclimates in your yard? Reflected light off a picture window or pool? Cold corners on the north side? Sun-baked south-facing walls? Wet sites below rain scuppers?
Fourth, what is the purpose of the tree in your landscape? It can be various: shade, background, block an unsightly view, frame a nice view, provide sound abatement, aesthetic appeal, fruit, or monetary — to help increase home value.
More than 4,000 trees can be grown relatively easily in our area — trees with vastly differing shapes, sizes, forms, leaf textures, flowering habit, leafing habit, fruiting characters, thorniness, degrees of allergenicity, aesthetic appeal and litter creating ability.
All characteristics of the tree must be considered. A tree that sheds litter constantly should not be placed near a pool. If you ask a nursery person for a shade tree, neglecting to mention the pool, they might recommend mesquite.
Before you go to the nursery to pick the perfect tree, make a list of all your needs and the site characteristics.
• Aesthetics. Any tree in your space should be aesthetically appealing to you. Love purples and pinks? A desert willow or ironwood might be nice. Both are pollinator friendly.
• Health. Fruiting olive and mulberries have been banned here, but far more allergenic ashes, cedars, and junipers are still legal and widely sold. Avoid planting such allergen producers within 50 feet of your windows.
• The site. Try to match the overall character of the tree with the character of your home. A Santa Fe style home would look great with a mesquite tree, but an Italianate villa might look better with a rounded formal evergreen oak or mastic tree.
• Care needs. Plant people call these “cultural requirements.” Consider how much care you want to provide. Water, fertilizer, pruning, litter, frost protection?
All trees need water. If the summer or winter rains don’t provide enough water, you will have to add some. Some species are fine with drip irrigation, but some need a deep soak every three weeks in summer (like citrus and pecan). Are you the kind of person that will remember to do this?
Soil type affects care needs. Our alkaline soils are fine for many trees, but some need a more acid soil (notably citrus and bottlebrush). Without repeat applications of soil acidifiers, these trees suffer.
Your tolerance for litter. All things considered, sometimes a deciduous tree may be less messy than an evergreen. For instance, the evergreen Emory oak (Quercus emoryi), always has some leaves on it, but it also always drops leaves. Every day. In season you also get the acorns. If you mind litter, avoid this tree.
A tree can add so much to your yard, and with all the species out there, it can be hard to decide which one to plant. By considering the character of the tree, the character of the site and your own character, you can find that perfect tree for your yard.
Jacqueline Soule, Ph.D., has been writing about gardening in our region for over three decades. Her most recent book is “Month by Month Guide to Gardening in Arizona, Nevada and New Mexico” (Cool Springs Press, 2016), a companion volume to “Southwest Fruit & Vegetable Gardening (Cool Springs Press, 2014).