Asked April 13, 2020, 4:36 PM EDT
Washington County Oregon
Sarah, congratulations on your new home.
Since your arborvitae is well established it should only require supplemental irrigation during prolonged periods of drought. If you see foliage drooping, or turning a lighter shade of color during dry weather, this could be a sign your plant could use a good deep soaking.
Directly watering to the root zone is optimal, hence the drip irrigation recommendation, besides it conserves water. But when watering with an automated irrigation system it's best to set your timer to water during the early morning hours and not in the late evening or at night, which can lead to the onset of fungus and other foliar diseases.
Generally, under good conditions, soil and watering, arborvitaes do not need additional fertilization. However, if you find yourself needing to add supplemental nutrients, please follow the instructions from the link located inside this basic care article of arborvitaes from Garden Design.
Best of luck and happy gardening.