Hours & Admission. The Arboretum grounds are open every day of the year except December 25 from 8:00 a.m. to 5:00 p.m. Admission is free. The Visitor Center is open from 8:00 a.m. to 4:30 p.m.daily except for federal holidays November through February. Please note the Visitor Center will be open on January 1st but closed on January 2nd (holiday observed).