Tulip trees (Liriodendron) are deciduous members of the magnolia family. Although not a direct relative of the tulip family of lilies, Liriodendron are known as tulip trees because their blooms closely resemble those of tulips. A tulip tree can be an excellent addition to any outdoor area, but they are not immune to certain problems, such as insect infestation, fungal growth and mold infection. Yellowing and defoliating leaves, however, are typically an indication of only one problem: drought stress. Since tulip trees are drought intolerant, it is important to know how to spot and treat under-watering due to drought stress before it threatens the health and life of your tulip tree.
Tulip trees do not have a high resistance to dry or drought conditions. Symptoms of too little water include leaves turning yellow and brittle, and withering at the edges. Eventually, the entire leaf turns yellow and brittle, and the leaf can be easily pulled off the branch. If left untreated, the leaves will wither to the point that they will defoliate on their own. These are symptoms of drought stress. Trees lose moisture through their leaves. In drought conditions, there is not enough additional moisture in the soil to replace that being lost through the leaves. Once the tree can no longer send sufficient moisture to its leaves, yellowing begins.
Giving the tree sufficient water relieves drought stress. Trees must be watered differently than plants. Plants need regular, brief supplements of water, whereas trees prefer prolonged, infrequent soakings. Coiling a soaker or mister garden hose around the base of your tree in a spiral starting from the trunk out to the outer edge of its branches achieves the needed saturation. Maintain 2- foot spacing between each spiral. The duration of the soaking largely depends on soil conditions. Leave the hose on until the entire area underneath the tree growth is soaked. Stick a piece of rebar or other metal straight down into the soil; if the soil has enough give to allow you to penetrate 6 inches to 1 foot, the soil is most likely saturated enough.
Preventative measures are more effective at managing drought stress in treatment after symptoms appear. If you live in a warm, dry climate with a prolonged dry season, deeply water the tree at least one per month during the dry season. Mulching is a very effective preventative tool. Mulch distributes soil moisture to the tree more efficiently and helps avoid water loss due to rainfall runoff. Two to 4 inches of mulch around the tree’s base help prevent drought stress.
In additional tulip trees, magnolias, Japanese maples, dogwoods, beeches, birches and other species are far less drought tolerant than some other species. If you live a climate that is prone to dry drought-like conditions, consider choosing a species of tree that is less labor-intensive to keep healthy. Query local nurseries and gardening stores as to the availability of drought-resistant cultivars of the species of tree you wish to plant outside.