For the first two weeks, water your new tree every other day by holding a hose around it and counting to 20. If you don’t have a hose, 2 large watering cans full of water will do (smaller trees may only need a light soaking so a single can may suffice).
During the second two weeks, switch to watering every three days with the same method mentioned above. After the first month, water once a week unless it is dry and hot (no rain and temperatures above 80 degrees). If it is hot and dry, water it twice a week. After the first six months, the trees will be established and won’t need any extra water. Your natural rainfall should be sufficient at this stage.
Your Thuja should not need any extra fertilizer unless your entire lawn and garden have problems and needs regular fertilizing. Apply a balanced tree and shrub fertilizer at the beginning of spring.
You won’t have to prune this tree if you are growing it with enough space for it to maintain its naturally graceful pyramid shape. If you’re growing several close together as a hedge, you can shear the plants yearly after the final frost.