When repotting your Holly plant, increase the pot size by 2". For instance, if your plant is in a 4" pot right now, upgrade to a 6" pot. This will give the roots more room to grow.
You can plant Holly outside in U.S. Department of Agriculture plant hardiness zones 5 through 8. Holly performs best in partial shade, although most types tolerate full sunlight. Water a newly planted holly as needed to keep the soil lightly moist. Holly benefits from a 2- inch layer of mulch, which moderates soil temperature, conserves moisture and controls weeds.