Thank you for using Michigan State University Extension with your Catalpa tree question. The most likely cause of the large vertical crack in your tree is a frost crack or sunscald. This happens when there are rapid temperature fluctuations. On warm, sunny winter days, the bark will warm up causing the cells to expand in the bark and wood directly below the bark. If the temperatures drop very quickly, the bark cools and contracts. The wood under the bark does not cool as quickly, causing the bark to split. A similar situation can occur during hot summer months when temperatures drop quickly at sunset. This damage shows up on the southwest or south side of the tree because that’s where the sun rays directly shine on the trees.

https://www.canr.msu.edu/news/frost_cracks_and_winter_damage_to_trees

https://www.canr.msu.edu/news/frost_cracks_in_trees

Determining the extent of the crack in your Calapa can be a waiting game to see the tree’s response. Sometimes trees grow protective tissue or callus over the crack. This response by the tree helps to protect itself from pathogens such as fungi or insect damage which can lead to decay. Once cracks have occurred in the bark it is important to assess and monitor. Because this is such a large crack and you have safety concerns, I would recommend that you contact a certified arborist to visually inspect and thoroughly assess the tree. An arborist who as a “risk assessment certification” would be able to assist in decision making about the safety of the tree. The following link is a great resource to help you find a local certified arborist.

www.treesaregood.org

If the arborist thinks that you can continue to monitor and enjoy your tree, there are other gardening practices that may help support the health of your tree:

• 2-3 inches of mulch of the root area of the tree, keeping mulch 5-6” away from the trunk
• Water the tree during long dry spells
• Avoid fertilizing in the fall

If you should need to replace your maple tree, a good way to prevent frost cracks in young trees is by wrapping the trunk in a light-colored tree wrap in the fall. This wrap needs to be removed as soon as danger of extreme cold in the spring has passed, as they can harbor insects and diseases. Other strategies to prevent frost cracks/sunscald is to place your tree in a more sheltered area or to place smaller plants to nearby to shade the south side of your tree.

Wishing the very best for you and your tree.