Arborvitae plants normally do not need feeding. However, if new growth is very sparse or slow, an application of a balanced fertilizer containing all major nutrients is recommended.
When to Feed Arborvitae? It is also important to know when to feed arborvitae. Fertilizing arborvitae at the wrong time can lead to problems with the tree. You should fertilize your arborvitae during the growing season. Offer the first feeding just before new growth begins. Fertilize at the intervals recommended on the container. Stop fertilizing arborvitae one month before the first frost in your region.
Applying fertilizer for arborvitae trees correctly is a matter of following easy directions. The fertilizer container will tell you how much of the product to use per tree. To fertilize your trees, broadcast the recommended amount of fertilizer evenly over the root zone. Keep the granules well away from the plant’s trunk area. Water the soil beneath the tree well when you are done fertilizing arborvitae. This helps the fertilizer dissolve so that it is accessible to the roots.
Your arborvitae will need watering twice weekly for the first few months after planting, then weekly watering (about 1 inch of water) for the next year or so. Once established, make sure it gets about a half-inch of water weekly, either through rainfall or irrigation.
If desired, light pruning in the early spring can help your arborvitae remain neat and foster thicker growth. To do so, trim the leafy parts of the branch, making sure not to cut back to bare wood. Dead or diseased branches should be removed to prevent decay and improve air circulation.
In addition, you may prune your tree to maintain the natural shape of the shrub, which is wider at the bottom and tapering inward toward the top. Especially adventurous gardeners can even prune the shape to form spiral topiaries.
Here is some more info:

https://today.oregonstate.edu/news/arborvitae-stands-tall-easy-care-hedge