USDA zone 7 is the climactic sweet spot for growing Blue Atlas cedar. The species is consistently hardy in USDA zones 6 through 8, and occasionally so in the zone 9 regions of both California and Florida, according to the University of Florida. Zone 7 temperatures dip below freezing, which necessitates a two-tier irrigation strategy, treating the spring, summer and fall seasons differently than winter. While blue cedar can tolerate occasional drought conditions when there is ample room for the roots to stretch for water, the tree will perform best when not under drought stress.
Maintain evenly moist, but never consistently wet or water-logged, soil for your cedar. Water deeply once or twice per month from spring to fall. Scale back applied water when rains have been substantial enough to drench the soil. Increase watering when temperatures are hot and conditions are dry. Feel the soil if in doubt; and water when the soil is dry to the touch a few inches down. If the soil is wet on the surface do not add more water.
Prepare the tree for winter drought conditions by irrigating deeply several times in the fall at least three weeks before the first hard frost hits. This timing will allow the deep soil to become moist enough to sustain the roots over winter. In unusually dry winters or official drought conditions, water the tree lightly a few times during the season to help it cope. Water in the morning hours, before noon and on sunny days, to help the water move into the root zone before freezing on the surface.
Resume your regular irrigation regimen in the spring after the last hard frost has passed and the soil has thawed enough to easily absorb the water and release it to the roots. When spring rains are heavy, applied irrigation can often be delayed until late spring.
Mulch around the base of your blue cedar once or twice each year with several inches of an organic material such as compost, shredded bark or leaf mold. This will feed the soil over time as the material breaks down, but more importantly, it will prevent moisture loss due to evaporation and insulate the roots from temperature fluctuations.