The arborvitae plant (Thuja spp.) Is a large evergreen shrub or tree using scale-like green leaf arranged on its branches in flattened sprays. This flexible plant is generally dependable and easy-to-grow, so if a newly planted specimen has sections or leaf that start to turn brown, it’s important to recognize and fix the problem quickly.
If a newly planted arborvitae grows brown leaves or twigs, the most likely cause is transplant shock, a state that is brought on by loss of roots when the plant was dug up — it can last a couple of years and may kill the plant if it’s severe. Transplant shock can cause leaf scorch, a yellowing or browning of leaf, and branches may eventually begin dying back. The best way to deal with transplant shock is to keep the plant well-watered for your first couple of years. Ensure it gets about 1 inch of water per week, such as rainfall, particularly during its initial year, and add a 3-to-4-inch thick layer of mulch beneath it’s canopy to conserve soil moisture. Overwatering can cause root rot that also can cause foliage to die and brown back, so water only when the top couple inches of dirt feel dry to the touch.
Planting Depth Problems
It’s important to plant a new arborvitae in precisely the same depth as it was in its previous site. Planting too deep can cause root suffocation that contributes to brown leaf, however if it’s not deep enough, then that can expose roots, making them dry out and the plant to do poorly. To check planting depth, examine the trunk at ground level, scraping away dirt as needed, until you see the light-to-dark transition that marks the previous planting depth. If this transition is below the new soil line, the plant is too heavy. If it’s more than about 1 inch above the ground line and you see some visible roots in the surface, then it’s not deep enough. In any scenario, dig up the plant and re-plant it in the right depth.
Even though an arborvitae is generally easy-to-grow and pest-free, a very small pest known as the arborvitae leafminer can cause brownish foliage. This insect feeds within the scale-like leaves, injuring them and finally causing leaf at branch tips to flip tan, then brownish. During autumn and winter, cut off and destroy any infested, damaged twigs, using shears that you wipe with rubbing alcohol between cuts to avoid spread of plant infection. To get a severe problem, destroy leafminer larvae by spraying the plant thoroughly in mid-spring and in late-summer using an insecticide containing spinosad. Dilute a 0.5 percent focus at a rate of 2 fluid ounces per gallon of water, but check on product label for additional directions. Wear gloves to protect your hands, and spray on a windless afternoon to stop spread of this insecticide.
A Natural Occurrence
If you just notice browning of leaf on the inner part of a newly planted arborvitae from the autumn and the shrub’s outer components remain green, that is probably a normal process that occurs as the plant grows and drops leaf not subjected to sun. Winter weather could also result in browning of outer leaf on the side of this arborvitae that faces prevailing winds. Arborvitaes grow in regions of the U.S. that could experience severe winters. For example, the American arborvitae (Thuja occidentalis) and the cultivar “Techny” (Thuja occidentalis “Techny”) grow at U.S. Department of Agriculture plant hardiness zones 2 through 7 and 2 through 8, respectively. In the colder parts of their scope, winter temperatures frequently drop below zero degrees Fahrenheit. In these areas, a windbreak made of burlap attached to stakes driven in the ground can minimize winter damage.