Answer: I agree - overfertilizing your new thujas would be just as bad as ignoring them while they're trying to become established. Since you've already used quick start, all you need to do is water them deeply to help them become established. Usually they'll need about one inch of water a week, so a deep soaking once each week should be fine. If you overwater, you'll drive oxygen out of the soil and roots need oxygen as well as moisture. Soak the soil then wait 2-3 days and dig down to see how moist the soil has remained. If it's still moist 2-3 inches below the surface, you won't have to water for a few more days; if it is dryish, water, then wait a few days to see how it is retaining moisture. You probably will only have to water once a week, but it depends upon your soil type.
Best wishes with your new thujas!
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