Though it’s very adaptable to adverse conditions, it is considered to have weak wood and a brittle branch structure, and it can be a messy tree when it is dropping spent flowers or dried seed pods. While it may not be an ideal tree to grow for every location, northern catalpa is widely grown on residential properties and in parks and other open spaces throughout the country, thanks to fast growth, dense shade, and good tolerance for urban conditions. It is normally planted as a nursery container plant or ball-and-burlap specimen in fall or spring, but it is also an exceptionally fast-growing tree when started from seed. Even when planted from seed, you may have a 15-foot tree that is flowering and providing meaningful shade before you know it. You’ll want to be sure you’re not planting a northern catalpa where its flowers and seeds can drop on sidewalks, as they can be slippery. It is also a relatively brittle tree, especially as it gets older, which means you may face frequent cleanup after storms.
Light
This tree will grow best in both full sun and partial shade. It prefers a minimum of six hours of direct, unfiltered sunlight every day.
Soil
Northern catalpa grows best in a relatively moist, loamy soil with a slightly acidic pH, but it will tolerate nearly any soil that is well drained, even if the clay content is fairly high.
Water
These trees prefer to be fairly moist and can tolerate a wide range of moisture conditions, including some flooding. When the tree is young, water whenever the soil surface is dry. A mature tree requires less watering, such as a good rainfall or irrigation every week or so. Well-established trees can nicely handle short periods of drought.
Temperature and Humidity
Hardy in zones 4 to 8, an established northern catalpa tree tolerates both winter cold and fairly hot and dry summer conditions, provided the soil moisture is adequate.
Fertilizer
If the soil in your area happens to be rich and loamy, you may not need to fertilize your northern catalpa tree at all. However, when planting in clay or sandy soil, you should consider applying a standard 10-10-10 fertilizer a few weeks after planting. Fertilize again each spring while the tree is young.
Types of Catalpa
There are no common named cultivars of northern catalpa, but there is a closely related species, southern catalpa (Catalpa bignonioides), that occupies a similar role as a landscape tree in warmer growing regions. C. bignonioides is a smaller tree with purplish flowers and thicker leaves, and many people feel it is a better landscape specimen than the northern catalpa, which can be somewhat ungainly. Southern catalpa is hardy in zones 5 to 9. In zones where these two species overlap, landscape professionals often lean toward the southern catalpa as the preferable tree.
Pruning
Regular pruning is a required duty for these trees—both to remove dead or dying branches and eliminate hazards, as well as to manage its size and shape within your landscape. Thinning out the crown also promotes the wind moving freely through the crown, which is important to prevent damage due to high winds. Pruning a large tree is usually a job for a professional trimmer. Pruning for shape and size is best done during the winter or early spring dormant period.
Propagating Northern Catalpa
Seed-starting is quite easy for this tree, but northern catalpa can be also propagated by rooting stem cuttings taken in summer after the spring growth is established. Here’s how:
Growing Northern Catalpa From Seed
The seeds found inside the long, tubular pods are remarkably easy to plant and nurture into new trees. It’s not uncommon for the seeds to simply fall into surrounding soil and sprout up as volunteers. These volunteers can readily be dug up and transplanted into a new space. It’s also an easy matter to collect some of the seeds by peeling a ripened pod apart. The bean-like seeds can be stored up to two years in the refrigerator before you plant them in spring in a desired location. Or, you can start new plants indoors by planting seeds in pots filled with potting mix in late winter. The seeds should be just barely covered with soil or potting mix. Keep the seeds and growing medium lightly moist in a location with bright but non-direct light until they germinate. After sprouting, move the seedlings to a sunny location and keep them well watered as they are growing. Seeds started in pots in spring may be ready to plant in the landscape by fall. Or, they can be kept in the pot to overwinter and grow for another season until you’re ready to plant.
Common Pests and Plant Diseases
The only serious pest problem for northern catalpa is the caterpillar of the catalpa sphinx moth, which may badly damage the foliage when it feeds on leaves. The worm rarely does lasting damage to the tree, which usually recovers the following year. Northern catalpa trees usually do not have serious problems with diseases or insects, though they sometimes have issues with verticillium wilt, leaf spot, mildew, and twig blight.
How to Get Northern Catalpa to Bloom
Don’t worry if a young tree doesn’t flower immediately, as it’s not uncommon for it to take seven years or more before the tree is mature enough to flower and set seed. A mature tree that doesn’t flower may be reacting to conditions that are too shady, or to soil that is lacking in nutrients. Establishing a regular feeding routine may help the tree flower more robustly. A catalpa that suddenly stops blooming after years of normal flowering may be reacting to an unseasonable late frost that has killed the flower buds. This is not a cause for worry, as the tree will usually return to a normal blooming pattern the following spring.
Common Problems With Northern Catalpa
Most of the complaints about northern catalpa trees involve its growth habit and messy behavior.
Invasive Roots
Northern catalpa trees have wide-ranging, invasive roots that can infiltrate foundations, sewer lines, buckle retaining walls, or compromise underground swimming pools. For this reason, they should be planted far away from any structures the roots might affect. Large trees may need to be removed if they begin to cause problems.
Messy Growth Habit
Another behavior that you should know about before choosing this tree is the sheer messiness of the species. The spring flowers, beautiful while on the tree, can be a soggy, slippery, smelly mess when they fall onto a sidewalk, deck, patio, or driveway. The dried seed pods leave similar mess when they fall, and their sharp points can even cause pin-prick wounds as they plummet from the tree. The huge leaves, though providing excellent shade, require a lot of raking once they drop in fall. And even mild winds can leave your yard covered with sticks and twigs that fall from this brittle tree. In other words, know what you’re getting into before planting a northern catalpa.
Tree Has Become Too Large for its Space
It’s quite common for homeowners to underestimate the speed with which a catalpa tree can get quite large. And because this is a brittle tree prone to wind damage, it’s not a specimen you want hanging over your home or carport. A tree that is becoming too large can be reduced by a professional tree trimmer, but it’s likely you will need to remove the tree at some point if it is growing in a poor location.
Leaf Drop
A catalpa tree that suddenly drops much of its foliage can be telling you one of several things, some of them quite serious. In some cases, unusually hot, dry weather may cause a temporary leaf drop that, while disfiguring, does not kill the tree. It usually recovers the following year. But leaf drop accompanies by shriveled, dead branches may be in the early stages of the most serious fungal disease to affect catalpas, verticillium wilt. Like other less serious diseases, verticillium first announces its presence by curling, yellowing leaves, but rather than recovering, the tree’s damage gradually expands from the crown down. Another cause of leaf destruction is the feeding of catalpa worm—the larval stage of the catalpa sphinx moth. Complete defoliation is possible, but affected trees usually recover entirely the following year.
