Problem Trees to Avoid Planting in Connecticut

Connecticut is home to some of the most beautiful native trees you’d ever want to see. Think red maples in their flaming fall color, stands of golden birch, and cool, dark hemlock groves. And in addition to these native beauties, there are dozens of cultivars and adapted species that enhance our gardens and streetscapes (although we always prefer to plant a native tree whenever possible!).

Here are our top native trees recommendations:

• Native trees for Fall Foliage Color
• Native Trees for Spring Flowers 

But among the many beneficial trees that grow in Connecticut are non-native and invasive tree species that can out-compete native species or host destructive insect pests. Plus, there are plenty of tree species that cause a range of other problems when they’re planted in your landscape.

Read on to learn about some trees we recommend you avoid planting in favor of others that have better manners. Most of these are considered problem trees in CT and are prohibited from importation, movement, sale, purchase, transplanting, cultivation, and distribution under CT General Statutes §22a-381d.

The Connecticut Invasive Plant Working Group’s website has a complete list of invasive trees in Connecticut.

Norway Maple (Acer platanoides)

Native to Europe, the Norway Maple (Acer platanoides) is a familiar sight to many people. These trees have dark green leaves, dense crowns that cast welcome shade, and are often found in parks and along streets. The trees are fast-growing and tolerate a range of conditions.

The Problem with Norway Maples Trees

Their very adaptability is what makes Norway maples so problematic in our forests. Norway maples produce a lot of fruits in the form of samaras, or “winged keys” as they’re often called, which carry seeds on the wind. When their seedlings germinate in a forest setting, they outcompete native plants by growing quickly and shading other seedlings. Because they produce seeds earlier than other maples, Norway maples are quickly reducing the diversity of native forests in Connecticut.

Norway maples also make extensive, shallow root systems that cause headaches. Their surface roots prevent grasses and other plants from growing and can make mowing around the trees impossible. Their large and shallow roots are also notorious for pushing up sidewalks and driveways, requiring expensive repairs.

If you want to plant a maple, consider the very similar-looking Acer saccharum, the native sugar maple.

Tree of Heaven (Ailanthus altissima)

Ailanthus altissima, the Tree of Heaven, hails from temperate regions of China. Tree of Heaven can grow to 80’ in height and its dark-green, compound leaves look almost identical to sumac at first glance. It is hardy, drought-tolerant, grows in poor soil, and will sprout new trees from its spreading roots.

The Problem with Tree of Heaven

Tree of Heaven’s fast growth outcompetes other shrubs and trees. Plus, it uses allelopathy (its roots put out a chemical that kills other plants) to prevent other species from growing. This lets the tree dominate the landscape settings at the expense of native species.

If you crush the leaves or stems, they release a strong, unpleasant odor (some say it smells like cat urine). It will grow through cracks in the pavement, spreads by hundreds of thousands of seeds each year, and forms dense thickets by sending up suckers from its roots and resprouting after being cut down. It’s no wonder it has also been called “Tree of Hell” and “Stinking Sumac”!

But the main reason we don’t recommend planting or keeping any existing Trees of Heaven is that the tree is the primary host for the destructive Spotted Lanternfly (SLF). SLF is an invasive insect pest that no one can eradicate. SLF will attack and kill many forest and crop species, including Connecticut’s valuable fruit trees and grapes.

Under Connecticut’s General Statutes pertaining to invasive plants, it’s illegal to buy or sell, transplant, cultivate, or otherwise grow this awful tree.

Autumn Olive (Elaeagnus umbellata)

Autumn olive is a tree-like shrub that grows to 20’, with multiple branches and an informal look. You can identify Autumn olive by its silvery, olive tree-like leaves and the abundance of sparkling, edible red berries that appear in early fall. Many people (and animals) value Autumn olive for its fruit and land managers have long used Autumn olive as a windbreak in tough settings.

The Problem with Autumn Olive

Autumn olives grow rapidly and will quickly take over open areas in fields, around woodlands, and next to ornamental plantings. It quickly shades out and kills nearby plants that need direct sunlight. They spread easily by seed, sprouting where animals leave behind the seeds of the fruit they’ve eaten. Plus, autumn olive is a “nitrogen fixer,” meaning that it can change soil fertility by adding nitrogen to the soil which harms native plant communities that depend on low soil fertility.

As with many invasive species, it’s easier to control these plants when they’re small. Connecticut’s Department of Environmental Protection (DEEP) recommends pulling or digging them out, although they also suggest using herbicides to control Autumn olive if necessary. However, we ask homeowners to seriously consider the damage herbicides can do to other important and threatened plant and animal species. If you plan on spraying, please read DEEP’s information on using herbicides.

Callery Pear (Pyrus calleryana)

You’ve probably seen lots of Callery pear trees as they’re widely used and popular for their spring flower display and fall color. They’re usually known by the name of the most popular cultivar, ‘Bradford’ pear. The trees are medium-to-large-sized (30-50’ tall) with shiny, dark-green leaves that turn orange and red in fall. In spring, the trees burst with clusters of white flowers that smell vaguely unpleasant and produce small fruits that birds eat (and disperse).

The Problem with Callery Pear (Bradford Pear)

Developers and designers have long liked using Callery pears in urban and suburban neighborhoods because they grow quickly. But unless you have these short-lived trees pruned regularly and thoroughly from an early age, Callery pears develop a dense crown that’s full of brittle, crossing branches. These branches often break and drop without warning, both during winter storms and at any time of year. Plus, the canopy is prone to splitting in half because of the narrow branch crotches.

Many states already consider Callery pears invasive because they can spread aggressively (although it’s not yet listed as an invasive tree in Connecticut). When they germinate in natural areas, Bradford pears quickly form dense, thorny thickets that are almost impossible to eradicate. These trees put out their flowers and leave early in spring, before other native species, which shades out those other trees just their leaves are emerging. This shading puts native trees at an immediate disadvantage as they’re not able to generate enough energy through photosynthesis to survive our hot summers and frigid winters.

Princess Tree (Paulownia tomentosa)

The Princess tree looks a lot like the well-behaved midwestern native catalpa. It has large, heart-shaped leaves and clusters of big, showy pink flowers in spring. Princess trees are tough, aggressive trees that grow in many places and are especially invasive in areas of disturbed soil, such as forest edges and roadways.

The Problem with Princess Trees

Princess trees are large, growing to 60’, and make a dense shade that few plants can grow in. It has brittle wood and branch drop is common. The tree also produces thousands of seeds that spread easily by wind and water. If a Princess tree is damaged or cut down, it will sprout from roots and re-grow. Because the tree can tolerate drought, poor soil, and acidic soils, it can grow almost anywhere. Its fast growth rate means that the Princess tree will out-compete native tree species and reduce forest and woodland diversity.

We recommend that you pull any sprouts you find and use herbicide to kill larger trees. Connecticut considers this tree invasive, so don’t plant this pest!

White Poplar (Populus alba)

The white poplar tree is fast-growing, makes a lot of suckering growth, and can reach 80’ in height. It’s also tolerant of poor soils and pollution, which is why it’s often found in urban settings. You’ll see white poplars often used as windbreaks and for erosion control along stream banks and roadsides.

The Problem with White Poplar

Its fast growth and brittle wood mean that white poplars tend to drop their limbs, resulting in expensive branch clearing after storms and the possibility of property damage and injury to people. Poplar trees have shallow roots that push up sidewalks and damage underground pipes. The tree is also susceptible to insect damage from aphids and scale, and foliage diseases including rust and powdery mildew.

The state of Connecticut has banned the white poplar because of its invasive habit. White poplar’s fast growth and ability to naturalize and sucker means it can easily overtake other native species. This leads to less forest diversity and fewer resources for the insects and wildlife that depend on native plants.

Black Locust (Robiniapseudoacacia)

Black locusts are medium-sized trees that reach 40’ though they can grow larger. They have attractive blue-green, compound leaves, with pairs of oval leaflets that make dappled shade in summer and add yellow color to the fall landscape. In spring, black locusts put out large, showy fragrant white flowers that hang down among the leaves.

The Problem with Black Locust

Brittle branches are an issue with this tree species, and branches will often drop in storms or during windy weather. If you prune your black locust regularly, you’re more likely to have fewer branches drop, and you can control the height and spread of the tree’s crown. The natural thorns that grow on this tree’s branches are another reason to prune your locust regularly—no one wants a chance encounter with them.

Black locust is in the pea family, which you might recognize by its flowers that resemble sweet pea blooms. This family tie means that the tree is a nitrogen fixer, meaning that it enriches or “fixes” soil with nitrogen that plant roots can take up. While this is beneficial for some soils, black locusts can spread into ecosystems with trees and plants that prefer less rich soil and disrupt their health.

Want a problem tree removed?

As Licensed Connecticut Arborists, we can take down any tree that’s causing your problems. If you’re not ready to remove a tree, we can prune and improve the health of your trees and make sure there are no branches or roots that pose safety risks. Even if your trees are on our list of problem trees, we’ll still treat them right!