We planted two long rows of swamp cedar hedge 4ft or so in height last summer. We watered them well and regularly and they did great over the winter. So this is our second summer coming up. How much and how often do we need to water them?
Your swamp, or Northern White Cedar [Thuja occidentalis] is native to eastern-southeastern Canada, and grows best in a wide variety of well-drained soils. Your hedge will need regular watering, particularly during dry periods, for the first couple of years. While it frequently grows in swamps in a natural setting, the article stresses the benefit of well-drained sites. It is recommended that leaf litter, commercial manure or well-rotted compost be applied to the soil as a mulch to prevent moisture loss and to hinder weed growth. The mulch should be applied several inches or about 10 cm away from the tree trunks.
Related questions that have been asked of Toronto Master Gardeners, https://www.torontomastergardeners.ca/askagardener/swamp-cedars-in-winter/
We wish you well in cultivating a lush cedar hedge.