Northern catalpa (Catalpa speciosa), a fast-growing deciduous tree, produces glossy, heart-shaped leaves. In spring, the leaves form a background for clusters of white, bell-shaped flowers. Large, bean-shaped seed pods form on the tree in fall and stick around all winter to drop in early spring, which can cause a litter problem along with the dropped flowers and fall leaves. You can plant northern catalpa in U.S. Department of Agriculture plant hardiness zones 4 through 8. Plant in spring, after the danger of frost has passed.
Where to Plant
A northern catalpa grows fast, averaging 1 foot of growth per year for the first 20 years. Eventually, the tree will reach a height of 40 to 70 feet with up to a 50-foot spread. Take this mature size into consideration when deciding where to plant the tree. The root system will be at least as wide as the canopy -- 50 feet. The tree needs full or partial sun and a moist, well-draining soil with a pH between 5.5 and 7.0, although northern catalpa is more tolerant of alkaline soils as it ages.
After contacting utility companies to have underground utilities marked, dig a hole about three times as wide and at an equal depth as the tree root ball. Mix 1 part compost or aged manure in with the soil. If your soil has a high pH use sphagnum peat moss to lower the pH. Place the tree in the center of the hole so the top of the roots are equal to or slightly above the soil line. Backfill with the amended soil until the roots are covered. Water the soil and add more as the soil settles. Do not press the soil down around the roots.
Water and Fertilizer
A 2- to 3-inch layer of mulch in a 3-foot radius around the tree will help keep the soil moist as well as eliminate competing grass and weeds. Water the northern catalpa when the top 1 to 2 inches of soil are dry. The frequency of watering will vary based on the type of soil, the temperature and the amount of rain. Fertilize the tree the first spring after planting. In absence of a soil test, use 1 cup of a balanced, 10-10-10 granular fertilizer spread over the root zone. Water the fertilizer into the soil after spreading it.
Pruning and Pests
Remove any dead branches you see, but otherwise avoid pruning the newly planted northern catalpa tree so it retains its leaves for better growth. Cut the branch with pruning shears just outside the branch collar, which is where the branch meets the trunk or a main branch. Northern catalpas are mostly pest-free, but catalpa sphinx moth (Ceratomia catalpae) caterpillars will strip a tree, so remove them if you see them. On a small tree, it should be easy to pick the caterpillars off by hand.