If they are very young ones, ie, a new hedge, as often as is necessary according to the weather to keep them constantly moist at the roots. Don't allow them to get dry fully or they might die. You will need to water them slightly less often if you apply a mulch around the base of each (a good idea) as it will help to preserve water in the soil.

thanks for that . i am very new to this gardening lark and imagine i will be asking more, probably very obvious and basic questions so cheers.