Choosing a Shade Tree!

I've tried to make lists of "good" and "bad" trees over the years. Really, there aren't bad trees (or puppies!)--there are just trees planted in the wrong places. On a recent house call I saw a mature Silver maple planted 6' from the house, with large roots extending towards the foundation and towards the neighbor's pool. A decision someone made twenty years ago will now cost the new owner thousands of dollars. By the way, this was a good reminder to have a certified arborist evaluate the trees on the property you're considering buying.

You should consider several things when choosing a tree. More important, you should set your priorities among these criteria. "I want a tree that grows fast, doesn't get too big, has nice flowers and fall color, isn't messy, has deep roots, and is low-maintenance!" This is unrealistic, so which of the following are most important to you?

Pest resistance and other maintenance issues (pruning, fertilizing). Some trees need to be sprayed to prevent pests. Others simply don't grow readily here in Davis because of our hard water--Japanese maples need regularly feeding with an acidic fertilizer, Liquidambars show chronic iron deficiency, and Tupeloes (Nyssa sylvatica) and Dogwoods (Cornus florida) get such bad leaf burn from the salts in our water that they never look good.

Growth rate and eventual size and shape. Most trees that grow very fast have significant drawbacks. Poplars, cottonwoods, and willows have invasive roots, break in the wind, and get borers. Mulberries create such dense shade that hardly anything grows under them. On the other hand, sycamore hybrids (Platanus), Hackberries (Celtis spp.) and Dawn redwood (Metasequoia glyptostroboides) grow fast and have few drawbacks, so they might be good choices if you need shade quickly.

Sometimes customers are concerned about a tree getting "too tall." I'm never quite sure what this means--trees are supposed to be tall! The shade pattern will affect the rest of the garden and landscape, so the trees you choose are your first and most important design decision in a new landscape. Of course, trees planted under power lines should not grow more than 15', or the utility will have to prune them and the results will not be pretty. Tall shrubs are probably more suitable under power lines.

Nice fall color, or seasonal flowers are always a nice bonus. Two of the best for fall color in Davis are Chinese pistache (Pistacia chinensis) and Maidenhair tree (Ginkgo biloba). Both are excellent shade trees. Calleryana pears (Pyrus calleryana) also have vivid fall color, but require careful pruning and training. New hybrid maples (Acer x freemanii) have been introduced that have bright red fall color, grow moderately fast, and have not shown invasive root systems.

Little-leaf linden (Tilia cordata) is a moderate grower with a somewhat formal look, with very pretty yellow fall color. European birch are graceful and have soft yellow fall color--but they need plenty of water! The trees in the older parts of east Davis with the beautiful golden yellow fall leaves are Modesto ash, a tree which was very popular in the 60's and 70's but which is no longer recommended due to blight disease and a susceptibility to mistletoe.

Spring-blooming trees are spectacular accents in the landscape, and are mostly small to medium-sized. Flowering plums, cherries, and crabapples are among the most prolific. Flowering cherries need good drainage, which can be a challenge in the heavy soil parts of Davis (west and north especially), but crabapples are particularly tolerant of heavy and wet soils. Deciduous magnolias (Magnolia soulangeana and stellata in particular) grow well if they get regular irrigation and occasional feeding with an acid fertilizer. Western redbud (Cercis occidentalis) is a good choice in dry landscapes.

Crape myrtles and Rose of Sharon (Hibiscus syriacus) provide the showiest summer bloom. While both are usually thought of as small trees, a few of the newer hybrids of Crape myrtle (Lagerstroemia) are big and fast enough to use as shade trees: 'Natchez' is pure white and grows to 30', and 'Tuscarora' is coral pink and grows to 25'.

Messiness (litter) and roots (shallow, invasive, or deep). Let's face it, trees drop stuff and litter is a nuisance. Older varieties of red-leaf plums and Aristocrat pears set pulpy, messy fruit, but other related varieties are nearly fruitless or have dry fruit that doesn't drop. Pagoda tree (Sophora japonica), Tallow tree (Sapium sebiferum), and Silk tree (Albizzia julibrissin) are all graceful and attractive trees, but they have messy blooms and pollen over a long period, and drop seed or sticky pods. Evergreen magnolias drop large, leathery leaves all season, and the flowers, while showy, are messy. Evergreen oaks such as Cork oak (Quercus suber) have a heavy leaf drop in the spring.

Invasive roots break sprinkler lines and buckle sidewalks--they're a liability. Silver maples(Acer saccharinum) are notorious for this and should not be planted in small residential areas. One that I'm seeing more and more in this regard is the aforementioned Sapium. Widely planted in the 70's and 80's, Sapium is proving to have shallow, aggressive roots when planted in irrigated areas. It is also reseeding in riparian areas, so tree experts should seriously reconsider recommending it.

Evergreen trees are not usually considered as shade trees, because we generally want winter sunlight, but some can be used to screen the two-story windows that are looking down into your back yard. They also help create windbreaks, which is especially important in new neighborhoods. Some of these trees get very large, and the dense, year 'round shade can be hard to garden under!

Evergreens are either conifers or broad-leaved. Some of the most successful conifers are Coast redwoods (Sequoia sempervirens, especially 'Soquel' and 'Aptos Blue'); Deodar cedar (Cedrus deodara), Incense cedar (Calocedrus decurrens), and many species of pines. Bay laurel (Laurus nobilis) is a very reliable broad-leaved evergreen with dark, shiny leaves and a columnar growth habit. Remember that most evergreens drop leaves or needles in small amounts, but steadily, all the time. This can be annoying near a pool, spa, or deck.