When the locially dropped column is also physically dropped

Hi,
I have dropped a column (say column name is 'A') from the relation R. By
setting the attisdropped as true in the pg_catalog.pg_attribute table. But
the column is dropped locially not the physically. Can you please tell me
when this column will be physically also dropped. Is this column is
automatically physically dropped? or I have to run some command to dropped
it physically.

Thanks,
Rupesh Bajaj