How often should I water a newly planted tree?

FAQ
Question: 

How often should I water a newly planted tree?

Answer: 

The key to watering newly planted balled and burlapped and container-grown trees is to keep the plant’s rootball moist for several weeks after planting.  Water newly planted trees every day for 4 or 5 days and then gradually reduce the frequency of watering.  When watering, slowly apply water to the rootball and the surrounding soil.  A thorough watering every 7 to 14 days (in dry weather) should be sufficient 4 to 5 weeks after planting.  Continue this watering schedule through summer and into fall.  Small trees usually require watering for 1 or 2 growing seasons.  It may be necessary to periodically water large trees for 2 or 3 years.