Linden trees, especially American, Tilia americana and littleleaf, Tilia cordata, have been widely planted in urban areas because they are drought tolerant, durable and beautiful, and thrive is some of our toughest locations. However, aphid infestations on these lindens can be incredibly messy and a real nuisance. The “honeydew” under a street tree can appear as if it rained just beneath the canopy. Except in this case, the shiny area you see is sticky like glue, excretions from the aphids. This glaze of honeydew can be horrible for cars, sidewalks, and outdoor furniture.
A perfect solution to avoid this malady is to select a close relative, the silver linden, Tilia tomentosa, which does not attract aphids. As the species name implies, tomentosa is used to describe a woolly coating on the leaf formed by the tomentose hairs. Apparently, it is the hairs or woolly coating on the leaves that repel the little critters. So, there is no need to blacklist all lindens because of the aphids. Read More "Silver Linden Tilia tomentosa"
There are technically only a few trees that come close to the small tree category for utility planting these days, maturing at less than 15 feet tall. There are even fewer that are narrow and this short. The new Emerald Spire® crabapple, Malus x adstringens ‘Jefgreen’ fits the bill. Maturing at no more than 15 feet tall and 6 feet wide, this is truly a small tree. It has shown remarkable winter hardiness and solid disease resistance as far north as Manitoba for over 10 years, making it a zone 2 plant. Did you hear that, Alaska? Read More "Emerald Spire® Flowering Crabapple Malus x adstringens ‘Jefgreen’"
The magnificent Princeton elm, Ulmus Americana ‘Princeton’ is the ideal tree to plant where large soil volume and above ground space is available. This is a true American elm, not a hybrid, but selected from a specimen around 1922 and developed by Princeton Nurseries. It has a proven record of Dutch elm resistance and longevity on the street. Ironically, the Dutch Elm Disease that decimated most elm trees in the US was not introduced into the US until about 10 years later, and Princeton elm trees planted before this time are still around today. This selection is also resistant to the elm leaf beetle but may be susceptible to phloem necrosis and wet wood. Read More "Princeton Elm, Ulmus americana ‘Princeton’"
The large and fragrant flower of the common lilac is a fondly held memory and experience for many of us. Most often planted as a shrub, lilacs have also been grown in tree form for some time. However, they are not used as often as they should as a tree. In addition to the more familiar shrub forms, there are tree forms of this plant. As we get better at selecting small maturing trees for use in smaller spaces, tree lilacs Syringa reticulata and S. pekinensis are definitely ones to consider.
Tree lilacs are relatively small, at most about 20 to 30 feet tall and 15 to 25 feet wide. Leaves are opposite, single, entire, broad-ovate, 2 to 5 and half inches long and about half as wide. Leaves are dark green on top and grayish green and reticulate (netlike pattern) on the bottom. The undersides might also be glabrous or slightly pubescent.
Spring growth appears to be fresh, clean, and balanced. Newly emerging leaves have a wine colored hue, turning green as they expand. Read More "Tree Lilacs, Syringa Reticulata and S. Pekinensis"
Not long ago, I wrote of three Parrotia Persica cultivars worthy of note for your street tree list: ‘Ruby Vase,’ ‘Vanessa,’ and ‘Persian Spire.’ I have just come across another to add to this list, Golden BellTower™.
A friend and local tree grower, Ken Christianson at Chrishaven Trees in Burlington, Washington, discovered this tree nearly 24 years ago; unlike many new tree varieties, this one has a pretty good history and performance record. Ken describes the ‘Golden BellTower’ as more reliably upright and columnar than some other Parrotia cultivars. It appears to be a moderate to fast grower, reaching 30 feet tall and up to 10 feet wide in about 25 years. Many other trees claim those mature dimensions but do not always live up to them, usually growing wider with age.
If you are unfamiliar with the Parrotia, you may mistake the leaf for a witchhazel, not really a stretch since they are both in the Hamamelidaceae family. And although the straight species of Persian ironwood has been a favorite for many, it was limited for urban use because of its relatively broad and unruly form. The arrival of new cultivars with more reliable form like ‘Golden BellTower’ have changed the game.
An unusual feature from the other narrow cultivars is the gold to apricot fall color, lending “golden” to its name, BellTower. It should be noted that fall color can vary considerably because of regional soils, and climate. From my experience, I have seen fall color vary from spectacular to incredibly boring on the same tree from year to year depending on seasonal weather. This selection apparently leans towards the yellow spectrum with more reliable color each year.
Sourgum, Black Tupelo, or Black Gum, or whatever your common regional name is for Nyssa sylvatica, chances are you would plant more if you could get your hands on nice specimens. Sourgum’s biggest attraction is for its spectacular fall color. Its nemesis has been the irregular form that plagues successful growing and use of the species. Our nursery still has Nyssa sylvatica specimens that have grown with different forms: sparse, dense, weeping, upright, perfect and not so perfect. Do you recall some of those with leaders that suddenly took a 90 degree turn? Sometimes matching 10, 20, or 30 specimens for a street tree installation could be a challenge, if not impossible. However, several selected forms that have come out over the past several years give us lots of great new options. Here are the Nyssa sylvatica cultivars that are now most readily available:
In general terms, this eastern North American native tree tolerates wet conditions but does not require wet ground. It appears to tolerate drought but thrives in moist well-draining soils. Read More "Using Nyssa Sylvatica Cultivars"
And there I was, stopped in my tracks again while walking the nursery rows. Hot Wings maple, Acer tartaricum ‘GarAnn,’ with its bright red ‘whirlybird’ samaras showing up in tight bunches all over the crown, was like nothing I had ever seen. And even better, I find out this amazing show of color lasts for at least six weeks. The Hot Wings maple was developed by Colorado State University and introduced by Plant Select, so its origin is notable because of its challenging climate. Read More "Hot Wings Maple – Acer Tartaricum ‘GarAnn’"