When you're taking care of a newly planted arborvitae, it's important to keep an eye on the watering. These plants need consistent and thorough watering to establish a strong root system. Here's a general watering schedule you can follow to help your arborvitae thrive: In the first 10 days, you'll want to water it 2-4 hours per day. Then, in the second or third week, change the watering frequency to every other day. In the third to sixth week, you can water it every 3-4 days.