How to Prune Chinese magnolia?
Magnolia pruning should be carried out in midsummer when in full leaf

Chinese magnolia · Magnolia sieboldii subsp. sinensis
Grow in moisture-retentive, well-drained neutral to acid soil in sun or part shade with shelter from cold winds. Will grow in moist alkaline soils. Further magnolia cultivation advice
Magnolia pruning should be carried out in midsummer when in full leaf